Properties that are characteristic of amino acids. General amino acid formula. Acid-base properties

Amino acids, proteins and peptides are examples of the compounds described below. Many biologically active molecules include several chemically different functional groups that can interact with each other and with each other's functional groups.

Amino acids.

Amino acids- organic bifunctional compounds, which include a carboxyl group - UNSD, and the amino group - NH 2 .

Share α and β - amino acids:

In nature, they are mainly found α -acids. The composition of proteins includes 19 amino acids and an ode imino acid ( C 5 H 9NO 2 ):

The simplest amino acid- glycine. The rest of the amino acids can be divided into the following main groups:

1) glycine homologues - alanine, valine, leucine, isoleucine.

Getting amino acids.

Chemical properties of amino acids.

Amino acids- these are amphoteric compounds, because contain in their composition 2 opposite functional groups - an amino group and a hydroxyl group. Therefore, they react with acids and alkalis:

Acid-base conversion can be represented as:

It's no secret that a person needs protein to maintain a high level of life - a kind of building material for body tissues; proteins are composed of 20 amino acids, the names of which are unlikely to tell anything to an ordinary office worker. Every person, especially when it comes to women, has ever heard of collagen and keratin - these are proteins that are responsible for the appearance of nails, skin and hair.

Amino acids - what are they?

Amino acids (or aminocarboxylic acids; AMA; peptides) are organic compounds, 16% consisting of amines - organic derivatives of ammonium - which distinguishes them from carbohydrates and lipids. They are involved in the biosynthesis of protein by the body: in the digestive system, under the influence of enzymes, all proteins supplied with food are destroyed to AMK. In total, there are about 200 peptides in nature, but only 20 basic amino acids are involved in the construction of the human body, which are subdivided into nonessential and irreplaceable; sometimes there is a third type - semi-replaceable (conditionally replaceable).

Essential amino acids

Replaceable are those amino acids that are both consumed with food and reproduced directly in the human body from other substances.

• Alanine is a monomer of biological compounds and proteins. Carries out one of the main pathways of glucogenesis, that is, it turns into glucose in the liver, and vice versa. A highly active participant in metabolic processes in the body.
• Arginine - AMK, capable of being synthesized in the body of an adult, but not capable of being synthesized in the body of a child. Promotes the production of growth hormones and others. The only carrier of nitrogenous compounds in the body. Helps to increase muscle mass and reduce body fat.
• Asparagine is a peptide involved in nitrogen metabolism. In the course of reaction with the enzyme asparaginase, it cleaves ammonia and turns into aspartic acid.
• Aspartic acid - takes part in the creation of immunoglobulin, deactivates ammonia. It is necessary in case of malfunctions of the nervous and cardiovascular systems.
• Histidine - used for the prevention and treatment of gastrointestinal diseases; has a positive dynamic in the fight against AIDS. Protects the body from the harmful effects of stress.
• Glycine is a neurotransmitter amino acid. It is used as a mild sedative and antidepressant. It enhances the effect of some nootropic drugs.
• Glutamine - in a large volume An activator of tissue repair processes.
• Glutamic acid - has a neurotransmitter effect, and also stimulates metabolic processes in the central nervous system.
• Proline is one of the constituents of almost all proteins. They are especially rich in elastin and collagen, which are responsible for the elasticity of the skin.
• Serine - AMK, which is contained in the neurons of the brain, and also promotes the release of a large amount of energy. Derived from glycine.
• Tyrosine is a constituent of animal and plant tissues. It can be reproduced from phenylalanine by the action of the enzyme phenylalanine hydroxylase; the reverse process does not occur.
• Cysteine ​​is one of the components of keratin, which is responsible for the firmness and elasticity of hair, nails, and skin. It is also an antioxidant. May be made from serine.

Amino acids that are not capable of synthesis in the body are irreplaceable

Essential amino acids are those that are not capable of being generated in the human body and can only be supplied with food.

• Valine is AMK, which is found in almost all proteins. Increases muscle coordination and reduces the body's sensitivity to temperature extremes. Maintains the hormone serotonin at a high level.
• Isoleucine is a natural anabolic that, during oxidation, energizes muscle and brain tissue.
• Leucine is an amino acid that improves metabolism. It is a kind of "builder" of the protein structure.
• These three AMKs are part of the so-called BCAA complex, which is especially in demand among athletes. Substances in this group act as a source for increasing muscle mass, reducing fat mass and maintaining well-being during particularly intense physical activity.
• Lysine is a peptide that accelerates tissue regeneration, the production of hormones, enzymes and antibodies. Responsible for the strength of blood vessels, is found in muscle protein and collagen.
• Methionine - participates in the synthesis of choline, the lack of which can lead to increased accumulation of fat in the liver.
• Threonine - gives elasticity and strength to tendons. It has a very positive effect on the heart muscle and tooth enamel.
• Tryptophan - maintains an emotional state, as it is converted into serotonin in the body. Indispensable for depression and other psychological disorders.
• Phenylalanine - improves the appearance of the skin by normalizing pigmentation. Supports psychological well-being by improving mood and bringing clarity to thinking.

Other methods of peptide classification

Scientifically, the 20 essential amino acids are categorized based on the polarity of their side chains, i.e. radicals. Thus, four groups are distinguished: (but not having a charge), positively charged and negatively charged.

Non-polar are: valine, alanine, leucine, isoleucine, methionine, glycine, tryptophan, phenylalanine, proline. In turn, to the polar ones, which have negative charge include aspartic and glutamic acids. Arginine, histidine, lysine are called polar ones with a positive charge. Amino acids with polarity but no charge include cysteine, glutamine, serine, tyrosine, threonine, and asparagine directly.

20 amino acids: formulas (table)

Amino acid	Abbreviation
Asparagine
Aspartic acid
Histidine
Glutamine
Glutamic acid
Isoleucine
Methionine
Tryptophan
Phenylalanine

Based on this, it can be noted that all 20 in the table above) are composed of carbon, hydrogen, nitrogen and oxygen.

Amino acids: participation in the life of the cell

Aminocarboxylic acids are involved in biological protein synthesis. Protein biosynthesis is the process of modeling a polypeptide ("poly" - many) chain of amino acid residues. The process takes place on the ribosome - an organelle inside the cell, which is directly responsible for biosynthesis.

Information is read from a section of the DNA chain according to the principle of complementarity (AT, C-G), when creating m-RNA (messenger RNA, or i-RNA - messenger RNA - identically equal concepts), the nitrogenous base thymine is replaced by uracil. Further, according to the same principle, a transfer of amino acid molecules to the site of synthesis is created. T-RNA is encoded by triplets (codons) (example: UAU), and if you know what nitrogenous bases the triplet is represented by, you can find out which amino acid it carries.

Food groups with the highest AMK content

Dairy products and eggs contain important substances such as valine, leucine, isoleucine, arginine, tryptophan, methionine and phenylalanine. Fish, white meat have a high content of valine, leucine, isoleucine, histidine, methionine, lysine, phenylalanine, tryptophan. Legumes, grains and cereals are rich in valine, leucine, isoleucine, tryptophan, methionine, threonine, methionine. Nuts and various seeds will saturate the body with threonine, isoleucine, lysine, arginine and histidine.

Below is the amino acid content of some foods.

The largest amounts of tryptophan and methionine can be found in hard cheese, lysine in rabbit meat, valine, leucine, isoleucine, threonine and phenylalanine in soy. When compiling a diet based on maintaining normal AMK, one should pay attention to squid and peas, and the poorest in terms of peptide content are potatoes and cow's milk.

Lack of amino acids with vegetarianism

It is a myth that there are amino acids that are found exclusively in animal products. Moreover, scientists have found that plant-based protein is absorbed better by the human body than by the animal. However, when choosing vegetarianism as a lifestyle, it is very important to monitor your diet. The main problem is that one hundred grams of meat and the same amount of beans contain different amounts of AMA in percentage terms. At first, it is necessary to keep records of the amino acid content in the food consumed, then this should come to automatism.

How many amino acids should you consume per day?

IN modern world absolutely all foodstuffs contain nutrients necessary for a person, so you should not worry: all 20 protein amino acids are safely supplied with food, and this amount is enough for a person who leads a normal life and monitors his diet at least a little.

The athlete's diet must be saturated with proteins, because without them it is simply impossible to build muscle mass. Exercise leads to a huge depletion of amino acid reserves, which is why professional bodybuilders are forced to take special supplements. With intensive building of muscle relief, the amount of protein can reach up to one hundred grams of protein per day, but such a diet is not suitable for daily consumption. Any food supplement implies an instruction containing different AMKs in a dose, which should be read before using the drug.

The effect of peptides on the quality of life of an ordinary person

Protein requirements are not limited to athletes. For example, the proteins elastin, keratin, collagen affect the appearance of hair, skin, nails, as well as the flexibility and mobility of joints. A number of amino acids affect the body, keeping the balance of fat at an optimal level, provide sufficient energy for Everyday life... Indeed, in the process of life, even with the most passive lifestyle, energy is expended, at least for breathing. In addition, cognitive activity is impossible in the absence of certain peptides; maintenance of the psychoemotional state is carried out, including through the AMK.

Amino acids and sports

The diet of professional athletes involves a perfectly balanced diet that helps to maintain muscle tone. Designed specifically for those athletes who work on gaining muscle mass, they make life very easy.

As stated earlier, amino acids are the main building blocks of proteins required for muscle growth. They are also able to speed up metabolism and burn fat, which is also important for beautiful muscle relief. When exercising vigorously, it is necessary to increase the intake of AMA as it increases the rate of muscle building and reduces post-workout pain.

The 20 amino acids in proteins can be consumed both as part of aminocarboxylic complexes and from food. If you choose a balanced diet, then you need to take into account absolutely all grams, which is difficult to implement with a heavy workload of the day.

What happens to the human body when there is a shortage or excess of amino acids

The main symptoms of a lack of amino acids are considered: poor health, lack of appetite, brittle nails, increased fatigue. Even with a shortage of AMK alone, there are a huge number of unpleasant side effects that significantly impair health and productivity.

Supersaturation with amino acids can lead to disruptions in the work of the cardiovascular and nervous systems, which, in turn, is no less dangerous. In turn, symptoms similar to food poisoning may appear, which also does not entail anything pleasant.

In everything, you need to know when to stop, therefore, adherence to a healthy lifestyle should not lead to an overabundance of certain "useful" substances in the body. As the classic wrote, "the best is the enemy of the good."

In the article, we examined the formulas and names of all 20 amino acids, the table of the content of the main AMK in products is given above.

Amino acid properties can be divided into two groups: chemical and physical.

Chemical properties of amino acids

Depending on the compounds, amino acids can exhibit different properties.

Interaction of amino acids:

Amino acids as amphoteric compounds form salts with both acids and alkalis.

As carboxylic acids, amino acids form functional derivatives: salts, esters, amides.

Interaction and properties of amino acids with grounds:
Salts are formed:

NH 2 -CH 2 -COOH + NaOH NH 2 -CH 2 -COONa + H2O

Sodium salt of + 2-aminoacetic acid Sodium salt of aminoacetic acid (glycine) + water

Interaction with alcohols:

Amino acids can react with alcohols in the presence of hydrogen chloride gas, converting into ester... Esters of amino acids do not have a bipolar structure and are volatile compounds.

NH 2 -CH 2 -COOH + CH 3 OH NH 2 -CH 2 -COOCH 3 + H 2 O.

Methyl ester / 2-aminoacetic acid /

Interaction ammonia:

Amides are formed:

NH 2 -CH (R) -COOH + H-NH 2 = NH 2 -CH (R) -CONH 2 + H 2 O

Interaction of amino acids with strong acids:

We get salts:

HOOC-CH 2 -NH 2 + HCl → Cl (or HOOC-CH 2 -NH 2 * HCl)

These are the main Chemical properties amino acids.

Physical properties of amino acids

We list the physical properties of amino acids:

• Colorless
• Are crystalline
• Most amino acids have a sweet taste, but depending on the radical (R) may be bitter or tasteless
• Well soluble in water, but poorly soluble in many organic solvents
• Amino acids have the property of optical activity
• Melts with decomposition above 200 ° C
• Non-volatile
• Aqueous solutions of amino acids in an acidic and alkaline environment conduct an electric current

Amino acids(synonym aminocarboxylic acids) - organic (carboxylic) acids containing one or more amino groups; the main structural part of a protein molecule.

Depending on the position of the amino group in the carbon chain with respect to the carboxyl group (that is, at the second, third, and so on carbon atoms), α-, β-, γ-amino acids are distinguished, and so on. Many amino acids are found in living organisms in free form or in more complex compounds. Described approx. 200 different natural amino acids, among which about 20 are especially important, which are part of proteins (see). All amino acids found in proteins are α-amino acids and correspond to the general formula: RCH (NH 2) COOH, where R is a radical unequal in different amino acids attached to the second carbon atom of the chain. The amino group is also attached to the same carbon atom. So this carbon has 4 different substituents and is asymmetric.

Even before the discovery of amino acids as a special class of chemicals, French chemists Vauquelin and Robiquet (L. W. Vauquelin, P. J. Robiquet, 1806) isolated crystalline asparagine from asparagus juice, which is an aspartic acid amide (see) and is one of the amino acids in proteins.

The first natural amino acid (cystine) was discovered in 1810 in urinary stones by W. N. Wollaston; in 1819 J. L. Proust, making experiments on cheese fermentation, isolated crystals of leucine. In 1820, N. Braconnot obtained glycine from gelatin hydrolyzate, which had a sweet taste and was named glutinous sugar; only later was glycine classified as an amino acid. The discovery of Brakonno was especially important because it was the first case of obtaining Amino acids from a protein hydrolyzate; Later, the remaining amino acids contained in protein molecules were isolated and identified from protein hydrolysates.

Amino acids have a number of common properties: they are colorless, crystalline substances that usually melt with decomposition at relatively high temperatures, sweet, bitter or insipid in taste. Amino acids are amphoteric electrolytes, that is, they form salts with both acids and bases and have some properties that are characteristic of both organic acids and amines. Natural α-amino acids can rotate the plane of polarization to different degrees to the right or to the left, depending on the nature of the amino acids and environmental conditions, but they all belong to the L-series, that is, they have the same configuration of the α-carbon atom and can be considered as derivatives of L-alanine or , respectively, L-glycerol aldehyde. The variety of properties and nature of the radicals of various amino acids determines the variety and specific properties of both individual amino acids and the protein molecules they are part of. The chemical structure and the most important properties of natural amino acids found in protein hydrolysates are given in table. one.

Table 1. Chemical structure and physicochemical properties of the most common amino acids in living nature

Name	Rational name	Formula	Molecular weight	Melting temperature	Solubility in grams per 100 g of water at t ° 25 °
α-Aminopropionic acid		89,09	297 ° (with expansion)	16,51
α-amino-δ-guanidinevaleric acid		174,20	238 ° (with expansion)	Easily soluble
γ-α-amino succinic acid amide		132,12	236 ° (with expansion)	3.11 (28 °)
α-Aminosuccinic acid		133,10	270 °	0,50
α-aminoisovaleric acid (α-amino-β-methylbutyric acid)		117,15	315 ° (with expansion)	8,85
α-amino-β-imidazolylpropionic acid		155,16	277 ° (with expansion)	4,29
Glycine (glycocol)	Aminoacetic acid		75,07	290 ° (with expansion)	24,99
δ-amide-α-aminoglutaric acid		146,15	185 °	3.6 (18 °)
α-Aminoglutaric Acid		147,13	249 °	0,843
α-amino-β-methylvaleric acid		131,17	284 ° (with expansion)	4,117
α-aminoisocaproic acid		131,17	295 ° (with expansion)	2,19
α-, ε-Diaminocaproic acid		146,19	224 ° (with expansion)	Easily soluble
α-amino-γ-methylthiobutyric acid		149,21	283 ° (with expansion)	3,35
γ-Hydroxypyrrolidine- α-carboxylic acid		131,13	270 °	36,11
Pyrrolidine-α-carboxylic acid		115,13	222 °	162,3
α-amino-β-hydroxypropionic acid		105,09	228 ° (with expansion)	5,023
α-amino-β-paraoxyphenylpropionic acid		181,19	344 ° (with expansion)	0,045
α-amino-β-hydroxybutyric acid		119,12	253 ° (with expansion)	20,5
α-amino-β-indolylprop opionic acid		204,22	282 ° (with expansion)	1,14
α-amino-β-phenylpropionic acid		165,19	284 °	2,985
α-amino-β-thiopropionic acid		121,15	178 °	-
Di-α-amino-β-thiopropionic acid		240,29	261 ° (with expansion)	0,011

Electrochemical properties

Having amphoteric properties(see Ampholytes), amino acids in solutions dissociate both by the type of acid dissociation (giving up a hydrogen ion and charging negatively), and by the type of alkaline dissociation (by attaching an H-ion and releasing a hydroxyl ion), while acquiring a positive charge. In an acidic environment, the alkaline dissociation of amino acids is enhanced and salts are formed with acid anions. In an alkaline environment, on the contrary, amino acids behave like anions, forming salts with bases. It was found that Amino acids in solutions almost completely dissociate and are in the form of amphoteric (bipolar) ions, also called zwitterions or amphiions:

In an acidic environment, the amphoteric ion attaches a hydrogen ion, which suppresses acid dissociation, and turns into a cation; in an alkaline medium with the addition of a hydroxyl ion, alkaline dissociation is suppressed, and the bipolar ion becomes an anion. At a certain pH of the medium, which is not the same for different amino acids, the degree of acid and alkaline dissociation for a given amino acid is equalized, and in the electric field of amino acids does not move either to the cathode or to the anode. This pH value is called the isoelectric point (pI), which is the lower the more acidic properties of a given amino acid are, and the higher the more basic properties of the amino acid are expressed (see Isoelectric point). At pI, the solubility of the amino acid becomes minimal, so that it is easier to precipitate from the solution.

Optical properties

All α-amino acids, with the exception of glycine (see), have an asymmetric carbon atom. Such an atom is always the 2nd, or α-carbon, atom, all four valencies of which are occupied by different groups. In this case, two stereoisomeric forms are possible, which are mirror images of each other and are incompatible with each other, like the right and left hand. The diagram shows two stereoisomers of the amino acid alanine in the form of a volumetric image and the corresponding projection on the plane. The image on the left is conventionally considered to be the left configuration (L), on the right - the right configuration (D). Such configurations correspond to the left and dextrorotatory glyceraldehyde, which is taken as the starting compound when determining the configuration of the molecules. It was shown that all natural amino acids obtained from protein hydrolysates correspond to the L-series in the configuration of the α-carbon atom, that is, they can be considered as derivatives of L-alanine, in which one hydrogen atom in the methyl group is replaced by a more complex radical. The specific rotation of the plane of polarization of the light of individual amino acids depends both on the properties of the entire molecule as a whole, and on the pH-solution, temperature, and other factors.

The specific rotation of the most important amino acids, their isoelectric points and indicators of acid dissociation constants (pK a) are presented in table. 2.

Table 2. Specific rotation of the plane of polarization, apparent acid dissociation constants and isoelectric points of L-amino acids at t ° 25 °

Amino acid	Specific rotation		Acid dissociation constants			Isoelectric point pI
	aqueous solution	at 5 N. solution of hydrochloric acid	pK 1	pK 2	pK 3
Alanya	+1,6	+13,0	2,34	9,69		6,0
Arginine	+21,8	+48,1	2,18	9,09	13,2	10,9
Asparagine	-7,4	+37,8	2,02	8,80		5,4
Aspartic acid	+6,7	+33,8	1,88	3,65	9,60	2,8
Valii	+6,6	33,1	2,32	9,62		6,0
Histidine	+59,8	+18,3	1,78	5,97	8,97	7,6
		2,34	9,60		6,0
Glutamine	+9,2	+46,5	2,17	9,13		5,7
Glutamic acid	+17,7	+46,8	2,19	4,25	9,67	3,2
Isoleucine	+16,3	+51,8	2,26	9,62		5,9
Leucine	-14,4	+21,0	2,36	9,60		6,0
Lysine	+19,7	+37,9	2,20	8,90	10,28	9,7
Methionine	-14,9	+34,6	2,28	9,21		5,7
Hydroxyproline	-99,6	-66,2	1,82	9,65		5,8
Proline	-99,2	-69,5	1,99	10,60		6,3
Series	-7,9	+15,9	2,21	9,15		5,7
Tyrosine	-6,6	-18,1	2,20	9,11	10,07	5,7
Threonine	-33,9	-17,9	2,15	9,12		5,6
Tryptophan	-68,8	+5,7	2,38	9,39		5,9
Phenylalanine	-57,0	-7,4	1,83	9,13		5,5
Cysteine	-20,0	+7,9	1,71	8,33	10,78	5,0
Cystine				2,01	8.02 pK 4 = 8.71	5,0

Previously, the optical antipodes of L-amino acids, that is, D-series amino acids, were called "unnatural", but nowadays, D-series amino acids are found in some bacterial products and antibiotics. So, the capsules of spore-bearing bacteria (Bac. Subtilis, B. anthracis, and others) largely consist of a polypeptide built from D-glutamic acid residues. D-alanine and D-glutamic acid are part of the mucopeptides that form the cell walls of a number of bacteria; valine, phenylalanine, ornithine and leucine of the D-series are contained in gramicidins and many other peptides - antibiotics, etc. Stereoisomeric amino acids differ significantly in their biological properties, they are attacked by enzymes specific only to a certain optical configuration, do not replace or only partially replace each other in metabolism, and the like D-isomers (see), leucine (see), serine (see), tryptophan (see. ) and valine (see) are very sweet, while the L-stereoisomers of alanine and serine are moderately sweet, tryptophan is tasteless, and leucine and valine are bitter. The characteristic "meaty" taste of L-glutamic acid is absent in the D-form. Synthetic amino acids are usually racemates, that is, a mixture of equal amounts of the D- and L-forms. They are referred to as DL-amino acids. With the help of some special reagents or treatment with some enzymes, synthetic amino acids can be separated into D- and L-forms, or only one desired stereoisomer can be obtained.

Amino acid classification

The characteristic properties of individual amino acids are determined by the side chain, that is, the radical standing at the α-carbon atom. Depending on the structure of this radical, amino acids are subdivided into aliphatic (these include most amino acids), aromatic (phenylalanine and tyrosine), heterocyclic (histidine and tryptophan) and imino acids (see), in which the nitrogen atom standing at the α-carbon atom, connected to a side chain in a pyrrolidine ring; these include proline and hydroxyproline (see Proline).

Amino acids are divided according to the number of carboxyl and amine groups as follows.

Monoaminomonocarboxylic amino acids contain one carboxyl and one amine group; these include most of the amino acids (their pI is about pH 6).

Monoaminodicarboxylic amino acids contain two carboxyl and one amine groups. Aspartic and glutamic acid (see) have slightly acidic properties.

Diaminomonocarboxylic acids - arginine (see), lysine (see), histidine (see) and ornithine - in an aqueous solution dissociate mainly as bases.

By chemical composition substituent groups are distinguished: hydroxyamino acids (contain an alcohol group) - serine and threonine (see), sulfur-containing amino acids (contain sulfur atoms) - cysteine, cystine (see) and methionine (see); amides (see) dicarboxylic amino acids - asparagine (see) and glutamine (see) and the like. Amino acids with a hydrocarbon radical, such as alanine, leucine, valine and others, give proteins hydrophobic properties; if the radical contains hydrophilic groups, as, for example, in dicarboxylic amino acids, they impart hydrophilicity to the protein.

In addition to the amino acids already mentioned (see the table and the corresponding articles), more than 100 amino acids have been found in the tissues of humans, animals, plants and microorganisms, many of which play an important role in living organisms. So, ornithine and citrulline (refer to diaminocarboxylic amino acids) play an important role in metabolism, in particular in the synthesis of urea in animals (see Arginine, Urea). Higher analogs of glutamic acid have been found in organisms: α-aminoadipic acid with 6 carbon atoms and α-aminopimelic acid with 7 carbon atoms. Oxylysin was found in the composition of collagen and gelatin:

having two asymmetric carbon atoms. Of the aliphatic monoaminomonocarboxylic amino acids, α-aminobutyric acid, norvaline (α-aminovaleric acid) and norleucine (α-amnocaproic acid) are found. The latter two were obtained synthetically, but are not found in proteins. Homoserine (α-amino-γ-hydroxybutyric acid) is the highest analogue of serine. Accordingly, α-amino-γ-thiobutyric acid, or homocysteine, is a similar analogue of cysteine. The last two amino acids, along with lanthionine:

[HOOC-CH (NH 2) -CH 2 -S-CH 2 -CH (NH 2) -COOH]

and cystathionine:

[HOOC-CH (NH 2) -CH 2 -S-CH 2 -CH 2 -CH (NH 2) -COOH]

take part in the exchange of sulfur-containing amino acids 2,4-Dioxyphenylalanine (DOPA) is an intermediate product of the exchange of phenylalanine (see) and tyrosine (see). From tyrosine, an amino acid such as 3,5-diiodotyrosine is formed - an intermediate product of the formation of thyroxine (see). In the free state and in the composition of some natural substances, there are amino acids methylated (see Methylation) by nitrogen: methylglycine, or sarcosine, as well as methylhistidine, methyltryptophan, methyllysine. The latter was recently discovered in the composition of nuclear proteins - histones (see). Also described are acetylated derivatives of amino acids, including acetyllisine in the composition of histones.

In addition to α-amino acids, in nature, mainly in free form and in the composition of some biologically important peptides, there are amino acids containing an amino group at other carbon atoms. These include β-alanine (see Alanine), γ-aminobutyric acid (see Aminobutyric acids), which plays an important role in the functioning of the nervous system, δ-aminolevulinic acid, which is an intermediate product of the synthesis of porphyrins. Amino acids also include taurine (H 2 N-CH 2 -CH 2 -SO 3 H), which is formed in the body during the exchange of cysteine.

Getting amino acids

Amino acids are obtained by various methods, some of them are designed specifically for the production of certain amino acids. The most common general methods chemical synthesis of amino acids are as follows.

1. Amination of halogenated organic acids. The halogen derivative (usually a brominated acid) is acted upon with ammonia, as a result of which the halogen is replaced by an amino group.

2. Obtaining amino acids from aldehydes by treating them with ammonia and hydrogen cyanide or cyanides. As a result of this treatment, cyanohydrin is obtained, which is further aminated to form an aminonitrile; saponification of the latter gives an amino acid.

3. Condensation of aldehydes with glycine derivatives, followed by reduction and hydrolysis.

Individual amino acids can be obtained from protein hydrolysates in the form of sparingly soluble salts or other derivatives. For example, cystine and tyrosine are readily precipitated at the iso-electrical point; diamino acids are precipitated in the form of salts of phosphoric-tungsten, picric (lysine), flavianic (arginine) and other acids; dicarboxylic amino acids are precipitated in the form of calcium or barium salts, glutamic acid is released in the form of amino acids hydrochloride in an acidic medium, aspartic acid is in the form of a copper salt, and so on. For the preparative isolation of a number of amino acids from protein hydrolysates, chromatographic and electrophoresis methods are also used. For industrial purposes, many amino acids are obtained by microbiological synthesis methods, isolating them from the culture medium of certain bacterial strains.

Determination of amino acids

As general reaction for amino acids, a color reaction is most often used with ninhydrin (see), which, when heated, gives a violet color of various shades with different amino acids. Folin's reagent (1,2-naphthoquinone-4-sulfoic acid sodium), deamination with nitrous acid with gasometric determination of the released nitrogen according to Van Slike (see Van Slike methods) is also used.

The determination of individual amino acids, as well as the amino acid composition of proteins and free amino acids of blood and other body fluids and tissues, is usually performed by chromatography on paper or on ion exchange resins (see Chromatography) or electrophoresis (see). These methods allow for the qualitative and quantitative determination of small amounts (fractions of a milligram) of any amino acids using reference samples of these compounds as "witnesses" or standards. Usually, automatic analyzers of amino acids (see. Autoanalyzers) are used, which carry out a complete amino acid analysis of samples containing only a few milligrams of an amino acid in a few hours. An even faster and more sensitive method for the determination of amino acids is gas chromatography of their volatile derivatives.

The amino acids that enter the human and animal body with food, mainly in the form of food protein, occupy a central place in nitrogen metabolism (see) and provide the synthesis in the body of its own proteins and nucleic acids, enzymes, many coenzymes, hormones and other biologically important substances; in plants alkaloids are formed from amino acids (see).

In the blood of humans and animals, a constant level of amino acids in free form and in the composition of small peptides is normally maintained. Human blood plasma contains on average 5-6 mg of amino acid nitrogen (usually called amino nitrogen) per 100 ml of plasma (see Residual nitrogen). In erythrocytes, the amino nitrogen content is 11 / 2-2 times higher, in the cells of organs and tissues it is even higher. About 1 g of amino acids is excreted in the urine per day (Table 3). With an abundant and unbalanced protein diet, with impaired function of the kidneys, liver and other organs, as well as with some poisoning and hereditary metabolic disorders of amino acids, their content in the blood increases (hyperaminoacidemia) and noticeable amounts of amino acids are excreted in the urine. (see Aminoaciduria).

Table 3. Content of free amino acids in blood plasma and human urine

Amino acid	Blood plasma ( mg %)	Urine in 24 hours ( mg)
Amino acid nitrogen	5,8	50-75
Alanya	3,4	21-71
Arginine	1,62	-
Aspartic acid	0,03
Valine	2,88	4-6
Histidine	1,38	113-320
1,5	68-199
Glutamic acid	0,70	8-40
Isoleucine	1,34	14-28
Leucine	1,86	9-26
Lysine	2,72	7-48
Methionine	0,52
Ornithine	0,72	-
Strait	2,36
Series	1,12	27-73
Tyrosine	1,04	15-49
Threonine	1,67	15-53
Tryptophan	1,27	-
Cystine (+ cysteine)	1,47	10-21

Active transport of amino acids

An essential role in amino acid metabolism is played by active transport of amino acids against the concentration gradient. This mechanism maintains the concentration of amino acids in cells at a higher level than their concentration in the blood, and also regulates the absorption of amino acids from the intestine (during the digestion of protein foods) and their reabsorption from the renal tubules after urine filtration in the malpighian glomeruli. Active transport of amino acids is associated with the action of specific protein factors (permeases and translocases), which selectively bind amino acids and carry out their active transfer due to the breakdown of energy-rich compounds. Mutual competition of some amino acids among themselves for active transfer and its absence in other amino acids shows that there are several systems of active transport of amino acids - for individual groups of amino acids. Thus, cystine, arginine, lysine and ornithine have a common transport system and compete with each other in this process. Another transport system ensures the transfer of glycine, proline, and hydroxyproline across membranes, and, finally, the third system, apparently, is common for a large group of other amino acids.

The role of amino acids in nutrition

Man and animals use nitrogen in the metabolism, supplied with food in the form of amino acids, mainly in the composition of proteins, some other organic nitrogen compounds, as well as ammonium salts. From this nitrogen, various amino acids are formed in the body through the processes of amination and transamination (see Transamination). Some amino acids cannot be synthesized in the animal body, and in order to maintain life, these amino acids must necessarily enter the body with food. These amino acids are called essential. Essential amino acids for humans: tryptophan (see), phenylalanine (see), lysine (see), threonine (see), valine (see), leucine (see), methionine (see) and isoleucine (see .). The rest of the amino acids are classified as nonessential, but some of them are nonessential only conditionally. Thus, tyrosine is formed in the body only from phenylalanine, and if the latter is supplied in insufficient quantities, it may be indispensable. Similarly, cysteine ​​and cystine can be formed from methionine, but are required when this amino acid is lacking. Arginine is synthesized in the body, but the rate of its synthesis may be insufficient with increased demand (especially with the active growth of a young body). The need for essential amino acids has been studied in studies on nitrogen balance, protein starvation, food intake and more. Nevertheless, the need for them does not lend itself to precise accounting and can only be estimated approximately. Table 4 shows data on the recommended and certainly sufficient quantities of essential amino acids for humans. The need for essential amino acids increases during periods of intensive growth of the body, with increased breakdown of proteins in some diseases.

The belonging of an amino acid to nonessential or irreplaceable for different organisms is not entirely the same. So, for example, arginine and histidine, which are nonessential amino acids for humans, are indispensable for chickens, and histidine is also for rats and mice. Autotrophic organisms (see), which include plants and many bacteria, are able to synthesize all the necessary amino acids. However, a number of bacteria require the presence of certain amino acids in the culture medium. Known species or strains of bacteria that selectively require the presence of certain amino acids. Such mutant strains, the growth of which is ensured only when a certain acid is added to the medium, are called auxotrophic (see. Auxotrophic microorganisms). Auxotrophic strains grow on a medium that is otherwise complete at a rate proportional to the amount of added essential amino acid, therefore they are sometimes used for microbiological determination of the content of this amino acid in certain biological materials, for example, the Guthrie method (see).

A nutritional deficiency of one of the essential amino acids leads to impaired growth and general dystrophy, but the absence of some amino acids can also give specific symptoms. For example, a lack of tryptophan often gives pellagra-like phenomena, since nicotinic acid is formed from tryptophan in the body (in experimental rats with a lack of tryptophan, corneal opacity, cataract, hair loss, anemia are observed); lack of methionine leads to liver and kidney damage; lack of valine causes neurological symptoms and so on.

Adequate nutrition is provided with a balanced content of individual amino acids in food. An excess of some amino acids is also disadvantageous. Excess tryptophan leads to the accumulation of its metabolic product, 3-hydroxyanthranilic acid, which can cause bladder tumors. With an unbalanced diet, an excess of some amino acids can disrupt the exchange or use of other amino acids and cause the latter to be deficient.

Amino acid metabolism pathology

The most common cause of amnnoaciduria and hyperaminoacidemia is kidney disease associated with impaired excretion and reabsorption of the amino acid. A number of specific disorders of amino acid metabolism are associated with hereditary insufficiency of certain enzymes involved in their metabolism.

So, a rare, but long-known disease - alkaptonuria is caused by a deficiency in the body of an enzyme - homogentisic acid oxidase (one of the products of the intermediate metabolism of tyrosine). With alkaptonuria, homogentisic acid is excreted in the urine and, oxidizing in the air, stains it black. Although alkaptonuria is detected from infancy, the clinical impairments are insignificant and are reduced only to a greater susceptibility to a particular type of arthropathy (ochronosis). Another hereditary disorder of amino acid metabolism is phenylketonuria. In this disease, there is a deficiency or absence of the enzyme phenylalanine-4-hydroxylase, as a result of which the conversion of phenylalanine to tyrosine is impaired; tyrosine, which is normally not an essential amino acid, becomes indispensable in patients with phenylketonuria, since it cannot be formed from phenylalanine. Phenylketonuria is associated with severe clinical disorders, of which the most important is impaired development of the brain and, as a result, severe mental retardation, manifested with early childhood... The reason for these disorders is the excessive accumulation of phenylalanine in the blood (hyperphenylalaninemia) and in the urine, in particular the accumulation of its metabolic products, in particular phenylpyruvic acid (phenylketonuria), from which the name of this disease is derived. In crust, the development of neurological disorders caused by phenylketonuria is successfully mitigated by giving babies a special diet with very low phenylalanine content. Some of the most important hereditary disorders of amino acid metabolism are presented in table. five.

Table 5. The most important hereditary disorders of amino acid metabolism

Name	An enzyme whose deficiency causes metabolic disorders	The reason for the metabolic disorder	Some pathological manifestations
Tyrosinemia	P-hydroxyphenylpyruvic acid oxidase	Failure to convert p-hydroxyphenylpyruvic acid to homogentisic acid	Severe damage to the liver and renal tubules, often fatal in infancy
Histidinemia	Histidase (histidine-α-deaminase)	Failure to form urokinic acid from histidine. Elevated blood levels and urinary excretion of histidine and imidazole pyruvic acid	Defects in speech. Often some degree of mental retardation
Homocystinuria	Cystathionine synthetase (serine dehydratase)	Failure to form cystathionine from homocysteine ​​and serine. Elevated serum homocystine and methionine and abnormal urinary excretion of homocystine	Mental retardation, skeletal anomalies, lens ectopia, arterial and venous thromboembolism
Cystathioninuria	Cystathionase (homoserine dehydratase)	Failure to break down cystathionine to form cystine, α-ketobutyrate and ammonia. Significant excretion of cystathionine in the urine and its increased content in tissues and serum	Sometimes mental retardation and mental impairment
Leucinosis (maple syrup disease)	Branched-chain keto acid decarboxylase (decarboxylase)	Disruption of decarboxylation of keto acids (α-keto-isovaleric, α-keto-β-methylvaleric and α-ketoisocaproic), which are products of deamination of the amino acid valine, isoleucine and leucine, and the excretion of these keto acids and the corresponding amino acids in the urine	Distinctive urine odor reminiscent of maple syrup. A progressive neurological disorder with severe brain degeneration that usually begins shortly after birth and ends fatally within weeks or months. In milder cases, intermittent attacks of toxic encephalopathy and excretion of the named keto acids and amino acids in the urine
One type of goiter cretinism	Iodothyrosine deiodinase	Violation of deiodination of mono- and diiodotyrosine during the synthesis of thyroid hormone	Sharp enlargement of the thyroid gland, accompanied by severe hypothyroidism
Hypervalinemia	Valintransaminase	Violation of valine transamination; increased content of it in the blood and excretion in the urine	Developmental disabilities and mental retardation
Isovalerian acidemia	Isovaleryl-coenzyme A-dehydrogenase	Increased amounts of isovaleric acid (a product of valine deamination) in blood and urine	Recurrent bouts of acidosis and coma
Hyperprolinemia	Proline oxidase	Increased serum content and urinary excretion of proline due to impaired conversion to Δ 1 -pyrrolidine-5-carboxylate	In some cases, impaired renal function and mental retardation
Oxyprolinemia	Oxyproline oxidase	Impaired conversion of hydroxyproline to Δ 1 -pyrrolidine-3-hydroxy-5-carboxylate and increased serum and urine hydroxyproline	Severe mental retardation

A special place is occupied by pronounced aminoaciduria (see), arising as a result of a violation of the transport of amino acids and, accordingly, their absorption from the renal tubules and from the intestines. Such disorders include cystinuria, diagnosed by the excretion of cystine in the urine and its deposition in the form of stones and sediments in the urinary tract. In fact, cystinuria is associated with a violation of the general system of active transport of four amino acids - lysine, arginine, ornithine and cystine. With cystinuria, on average, more than 4 g of these amino acids are released per day, of which only about 0.75 g falls to the share of cystine, but it is cystine, due to its low solubility, that precipitates and causes the deposition of stones. Disruption of another system of active transport, common for glycine, proline and hydroxyproline, leads to an increased excretion of these three amino acids in the urine (without the appearance of signs of clinical disorders). Finally, the disturbance of another general system of amino acid transport, which apparently includes a large group of all other amino acids, called Hartnup's disease, is associated with a variety of clinical manifestations that are not the same in different cases of the disease.

Use of amino acids

Amino acids are widely used in medicine and other fields. Various sets of amino acids and protein hydrolysates, enriched with individual amino acids, are used for parenteral nutrition during operations, bowel diseases and malabsorption. Certain amino acids have specific therapeutic effects in various disorders. So, methionine is used for obesity of the liver, cirrhosis and the like; glutamic and γ-amino-butyric acids have a good effect on certain diseases of the central nervous system (epilepsy, reactive states, and so on); histidine is sometimes used to treat patients with hepatitis, gastric ulcer and duodenal ulcer.

Amino acids are also used as food additives. In practice, the most important are the addition of lysine, tryptophan and methionine to foods that are deficient in the content of these amino acids. The addition of glutamic acid and its salts to a number of products gives them a pleasant meaty taste, which is often used in cooking. In addition to human nutrition and the use of amino acids in the food industry, they are used for feeding animals, for preparing culture media in the microbiological industry, and as reagents.

Histochemical methods for the detection of amino acids in tissues

The reactions for the detection of amino acids in tissues are based mainly on the identification of amino groups (NH 2 -), carboxyl (COOH-), sulfhydryl (SH-) and disulfide (SS-) groups. Methods for the detection of individual amino acids (tyrosine, tryptophan, histidine, arginine) have been developed. Amino acids are also identified by blocking certain groups. It should be borne in mind that the histochemist deals, as a rule, with a denatured protein; therefore, the results of histochemical methods are not always comparable with biochemical ones.

To identify SH- and SS-groups, the best reaction is considered to be 2,2'-dioxy-6,6'-dinaphthyldisulfide (DDD), based on the formation of naphthyl disulfide a, bound to a protein containing SH-groups. To develop color, the drug is treated with a diazonium salt (strong blue B or strong black K), which combines with naphthyldisulfide, forming an azo dye that stains the areas of localization of SH and SS groups in tissues in shades from pink to blue-violet. The method allows for quantitative comparisons. The tissue is fixed in Carnois, Bouin's liquid, in formalin. The best results are obtained with a 24-hour fixation in a 1% solution of trichloroacetic acid in 80% alcohol, followed by washing in a series of alcohols of increasing concentration (80, 90, 96%), then dehydration and embedding in paraffin. The reaction requires reagents: DDD, diazonium salt, 0.1 M veronal acetate buffer solution (pH 8.5), 0.1 M phosphate buffer solution (pH 7.4), ethyl alcohol, sulfuric ether.

α-Amino acids are detected using Schiff's ninhydrin reagent. The method is based on the interaction of ninhydrin with amino groups (NH 2 -); the resulting aldehyde is detected by the Schiff's reagent. The material is fixed in formalin, anhydrous alcohol, Zenker's liquid, and is embedded in paraffin. Reagents required: ninhydrin, Schiff's reagent, ethyl alcohol. Tissues containing α-amino groups are painted in pinkish-crimson shades. The specificity of the reaction, however, is controversial, since not only α-amino acids, but also other aliphatic amines can be oxidized by ninhydrin.

Tyrosine, tryptophan, histidine are detected by the tetrazonium method. Diazonium salts in an alkaline medium are in the form of diazonium hydroxides, which bind to the named amino acids. To enhance the color coloration, the sections are treated with β-naphthol or H-acid. Fixation with formalin, Carnoy's liquid. Required reagents: tetrazotized benzidine or better strong blue B, 0.1 M veronal acetate buffer solution (pH 9.2); 0.1 n. HCl, H-acid or β-naphthol. Depending on the reagent, the sections are colored violet-blue or brown. When evaluating the results, one should bear in mind the possibility of adding phenol and aromatic amines to diazonium hydroxide. Control reactions are used to differentiate amino acids.

From Additional Materials

When writing the sequence of amino acid residues in the polypeptide chain, the International Union of Pure and Applied Chemistry and the International Biochemical Union proposed using abbreviated amino acid names, usually consisting of the first three letters of the full name of the corresponding amino acid (see table). The use of the international romanized standard system of symbols and abbreviations presents great advantages in terms of collecting, processing and retrieving scientific information, eliminating errors when translating texts from foreign languages, and the like. Unified abbreviated names of chemical compounds, including amino acids, are especially important not only internationally, but also for use within the USSR, where scientific literature is published in dozens of languages, different alphabetically, vocabulary and the outline of special terms and their abbreviations.

Abbreviated designations of free amino acids should not be used in the text of works, it is permissible only in tables, lists, diagrams.

Where the sequence of amino acid residues in the peptide chain is known, the symbols of the residues are written in order, connecting them with hyphens; That chain or part of a chain, where the sequence of joining amino acid residues is unknown, is enclosed in parentheses, and the characters of amino acid residues are separated by commas. When writing linear peptides or proteins, the symbol of the amino acid bearing a free amino group is placed on the left end of the established sequence (that is, at its N-end), and the symbol of the amino acid residue carrying a free carboxyl group at the right end (at the C-end). The polypeptide chain is preferably depicted horizontally rather than vertically. The amino acid symbols denote natural (L-) forms, their antipodes - the D- symbol, which is placed immediately before the amino acid symbol, without separating from it with a hyphen (for example, Leu-DFen-Gly).

The symbols of amino acids less common in nature are specifically specified in each publication. It is recommended to observe only the following principles, for example, hydroxyamino acids (hydroxyamino acids): hydroxylysine (hydroxylysine) - Hyl (Oly) and so on; allo-amino acids: allo-iso leucine - aile (aIle), allo-oxylysin - aHyl (aOli); noramino acids: norvaline-Nva (Hva), norleucine-Nle (Hle), etc.

Table. Abbreviated spelling of amino acids most common in nature

Full name of the amino acid	International Symbols	Symbols adopted in Russian scientific publications
Asparagine
Aspartic acid
Aspartic acid and l pi asparagine (if no distinction is established)
Hydroxyproline
Histidine
Glutamine
Glutamic acid
Glutamic acid or glutamine (if no distinction is established)
Isoleucine
Methionine
Tryptophan
Phenylalanine

Bibliography

Braunstein AE Biochemistry of amino acid metabolism, M., 1949, bibliogr .; Meister A. Biochemistry of amino acids, trans. from English., M., 1961; Greenstein J. P. a. Winitz M. Chemistry of the amino acids, v. 1-3, N. Y.-L. 1961; Meister A. Biochemistry of the amino acids, v. 1-2, N. Y. 1965; Nivard R. J. E. a. Tesser G. I. Amino acids and related compounds, Comprehens. Biochem., V. 6, p. 143, 1965, bibliogr .; Nomenclature biological chemistry, per. from English, ed. A.E.Braunstein, V. 1, p. 13, etc., M., 1968.

Histochemical methods for the detection of amino acids in tissues

Lilly R. Pathohistological technique and practical histochemistry, trans. from English, M., 1969, bibliogr .; Pierce E. Histochemistry, trans. from English, p. 73, M., 1962; Principles and methods of histocytochemical analysis and pathology, ed. A.P. Avtsyna, etc., L., 1971, bibliogr.

I. B. Zbarsky; R. A. Simakova (hist.), N. G. Budkovskaya.

Amino acids are the building blocks or building blocks of proteins that make up proteins. Amino acids are 16% nitrogen, which is their main chemical difference from the other two essential nutrients - carbohydrates and fats. The importance of amino acids for the body is determined by the huge role that proteins play in all vital processes.

Any living organism, from the largest animals to tiny microbes, is made up of proteins. Various forms of proteins are involved in all processes occurring in living organisms. In the human body, proteins form muscles, ligaments, tendons, all organs and glands, hair, nails. Proteins are found in fluids and bones. Enzymes and hormones that catalyze and regulate all processes in the body are also proteins. Deficiency of these nutrients in the body can lead to an imbalance in water balance, which causes swelling.

Each protein in the body is unique and exists for a specific purpose. Proteins are not interchangeable. They are synthesized in the body from amino acids, which are formed as a result of the breakdown of proteins found in food. Thus, it is amino acids, and not proteins themselves, that are the most valuable nutrients. In addition to the fact that amino acids form proteins that make up tissues and organs human body, some of them act as neurotransmitters (neurotransmitters) or are their precursors.

Neurotransmitters are chemicals that transmit a nerve impulse from one nerve cell to another. Thus, some amino acids are essential for the normal functioning of the brain. Amino acids help vitamins and minerals perform their functions adequately. Some amino acids directly provide energy to muscle tissue.

In the human body, many amino acids are synthesized in the liver. However, some of them cannot be synthesized in the body, so a person must definitely get them from food. These essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Amino acids that are synthesized in the liver: alanine, arginine, asparagine, aspartic acid, citrulline, cysteine, gamma-aminobutyric acid, glutamine and glutamic acid, glycine, ornithine, proline, serine, taurine, tyrosine.

The process of protein synthesis is ongoing in the body. In the case when at least one essential amino acid is absent, the formation of proteins is suspended. This can lead to a wide variety of serious problems, from indigestion to depression and stunted growth.

How does this situation arise? Easier than you might imagine. Many factors lead to this, even if your diet is balanced and you are consuming enough protein. Malabsorption in the gastrointestinal tract, infection, trauma, stress, certain medications, the aging process, and imbalances in other nutrients in the body can all lead to a deficiency of essential amino acids.

It should be borne in mind that all of the above does not mean that eating a large amount of protein will help solve any problems. In reality, this is not conducive to maintaining health.

An excess of proteins creates additional stress for the kidneys and liver, which need to process products of protein metabolism, the main of which is ammonia. It is very toxic to the body, so the liver immediately converts it into urea, which then enters the kidneys with the blood stream, where it is filtered and excreted.

As long as the amount of protein is not too high and the liver is working well, ammonia is neutralized immediately and does no harm. But if there is too much of it and the liver cannot cope with its neutralization (as a result of malnutrition, indigestion and / or liver disease), a toxic level of ammonia is created in the blood. In this case, a lot of serious health problems can arise, up to hepatic encephalopathy and coma.

Too high a concentration of urea also causes kidney damage and back pain. Therefore, it is not the quantity but the quality of the protein consumed with food that is important. Currently, it is possible to obtain essential and nonessential amino acids in the form of biologically active food additives.

This is especially important for various diseases and when using reduction diets. Vegetarians need supplements that contain essential amino acids so that the body gets everything it needs for normal protein synthesis.

There are different types of amino acid supplements available. Amino acids are part of some multivitamins, protein mixtures. Formulas are commercially available that contain complexes of amino acids or contain one or two amino acids. They come in various forms: capsules, tablets, liquids and powders.

Most amino acids come in two forms, with the chemical structure of one being a mirror image of the other. They are called D- and L-forms, for example D-cystine and L-cystine.

D stands for dextra (Latin for right), and L stands for levo (for left, respectively). These terms refer to the direction of rotation of the helix, which is the chemical structure of a given molecule. Proteins of animals and plants are created mainly by the L-forms of amino acids (with the exception of phenylalanine, which is represented by the D, L forms).

Food supplements containing L-amino acids are considered more suitable for the biochemical processes of the human body.
Free, or unbound, amino acids are in their purest form. Therefore, when choosing a supplement containing amino acids, preference should be given to products containing L-crystalline amino acids, standardized by the American Pharmacopoeia (USP). They do not need to be digested and are absorbed directly into the bloodstream. After oral administration, they are absorbed very quickly and, as a rule, do not cause allergic reactions.

Individual amino acids are taken on an empty stomach, preferably in the morning or between meals with a small amount of vitamins B6 and C. If you are taking a complex of amino acids that includes all essential amino acids, it is best to do this 30 minutes after or 30 minutes before meals. It is best to take both the individual amino acids you need and the amino acid complex, but at different times. Amino acids alone should not be taken for long periods of time, especially in high doses. Recommended to be taken within 2 months with a 2-month break.

Alanin

Alanine contributes to the normalization of glucose metabolism. A relationship has been established between an excess of alanine and infection with the Epstein-Barr virus, as well as chronic fatigue syndrome. One of the forms of alanine, beta-alanine, is an integral part of pantothenic acid and coenzyme A, one of the most important catalysts in the body.

Arginine

Arginine slows down the growth of tumors, including cancerous ones, by stimulating the body's immune system. It increases the activity and size of the thymus gland, which produces T-lymphocytes. In this regard, arginine is useful for people suffering from HIV infection and malignant neoplasms.

It is also used for liver diseases (cirrhosis and fatty degeneration), it promotes detoxification processes in the liver (primarily the neutralization of ammonia). Semen contains arginine, so it is sometimes used in the complex therapy of infertility in men. There is also a large amount of arginine in the connective tissue and in the skin, so its intake is effective for various injuries. Arginine is an important component of muscle metabolism. It helps to maintain an optimal nitrogen balance in the body, as it is involved in the transport and detoxification of excess nitrogen in the body.

Arginine helps reduce weight by causing some reduction in body fat stores.

Arginine is found in many enzymes and hormones. It stimulates the production of insulin by the pancreas as a component of vasopressin (pituitary hormone) and aids growth hormone synthesis. Although arginine is synthesized in the body, its production can be reduced in newborns. Sources of arginine include chocolate, coconuts, dairy products, gelatin, meat, oats, peanuts, soybeans, walnuts, white flour, wheat, and wheat germ.

People having viral infections, including Herpes simplex, should not take arginine supplements and should avoid consuming foods rich in arginine. Pregnant and breastfeeding mothers should not take arginine supplements. Taking small doses of arginine is recommended for diseases of the joints and connective tissue, for impaired glucose tolerance, liver diseases and injuries. Long-term use is not recommended.

Asparagine

Asparagine is necessary to maintain balance in the processes taking place in the central nervous system: Prevents both over-arousal and over-inhibition. It is involved in the synthesis of amino acids in the liver.

Since this amino acid increases vitality, a supplement based on it is used for fatigue. It also plays an important role in metabolic processes. Aspartic acid is often prescribed for diseases of the nervous system. It is useful for athletes, as well as for liver dysfunctions. In addition, it stimulates immunity by increasing the production of immunoglobulins and antibodies.

Aspartic acid is found in large quantities in vegetable proteins obtained from germinated seeds and in meat products.

Carnitine

Strictly speaking, carnitine is not an amino acid, but its chemical structure is similar to that of amino acids, and therefore they are usually considered together. Carnitine is not involved in protein synthesis and is not a neurotransmitter. Its main function in the body is the transport of long-chain fatty acids, the oxidation of which releases energy. It is one of the main sources of energy for muscle tissue. Thus, carnitine increases the conversion of fat into energy and prevents the deposition of fat in the body, primarily in the heart, liver, skeletal muscles.

Carnitine reduces the likelihood of developing complications of diabetes mellitus associated with disorders of fat metabolism, slows down fatty degeneration of the liver in chronic alcoholism and the risk of heart disease. It has the ability to lower blood triglyceride levels, promote weight loss and increase muscle strength in patients with neuromuscular diseases, and enhance the antioxidant effect of vitamins C and E.

Some muscular dystrophies are thought to be associated with carnitine deficiency. With such diseases, people should receive more of this substance than it should be according to the norms.

It can be synthesized in the body in the presence of iron, thiamine, pyridoxine and the amino acids lysine and methionine. Carnitine is synthesized in the presence of a sufficient amount of vitamin C. An insufficient amount of any of these nutrients in the body leads to a deficiency of carnitine. Carnitine enters the body with food, primarily with meat and other animal products.

Most cases of carnitine deficiency are associated with a genetically determined defect in the process of its synthesis. Possible manifestations of carnitine deficiency include impaired consciousness, heart pain, muscle weakness, and obesity.

Men, due to their greater muscle mass, require more carnitine than women. Vegetarians are more likely to be deficient in this nutrient than non-vegetarians because carnitine is not found in plant proteins.

What's more, methionine and lysine (amino acids essential for the synthesis of carnitine) are also not found in sufficient quantities in plant foods.

To get the right amount of carnitine, vegetarians must take dietary supplements or eat lysine-fortified foods such as cornflakes.

Carnitine is presented in dietary supplements in various forms: as D, L-carnitine, D-carnitine, L-carnitine, acetyl-L-carnitine.
It is preferable to take L-carnitine.

Citrulline

Citrulline is found primarily in the liver. It increases energy supply, stimulates the immune system, and is metabolized into L-arginine. It neutralizes ammonia, which damages liver cells.

Cysteine ​​and Cystine

These two amino acids are closely related, each cystine molecule is made up of two cysteine ​​molecules attached to each other. Cysteine ​​is very unstable and readily converts to L-cystine, and thus one amino acid readily converts to another when needed.

Both amino acids are sulfur-containing and play an important role in the formation of skin tissues, are important for detoxification processes. Cysteine ​​is found in alpha-keratin, the main protein in nails, skin and hair. It promotes collagen formation and improves skin elasticity and texture. Cysteine ​​is also found in other proteins in the body, including some digestive enzymes.

Cysteine ​​helps to neutralize some toxic substances and protects the body from the damaging effects of radiation. It is one of the most powerful antioxidants, and its antioxidant effect is enhanced when taken simultaneously with vitamin C and selenium.

Cysteine ​​is a precursor of glutathione, a substance that has a protective effect on liver and brain cells from alcohol damage, certain drugs and toxic substances contained in cigarette smoke. Cysteine ​​dissolves better than cystine and is utilized faster in the body, therefore it is more often used in the complex treatment of various diseases. This amino acid is formed in the body from L-methionine, with the obligatory presence of vitamin B6.

Additional intake of cysteine ​​is necessary for rheumatoid arthritis, arterial disease, cancer. It accelerates recovery after operations, burns, binds heavy metals and soluble iron. This amino acid also speeds up fat burning and muscle building.

L-cysteine ​​has the ability to break down mucus in the respiratory tract, which is why it is often used for bronchitis and pulmonary emphysema. It accelerates the healing process in respiratory diseases and plays an important role in the activation of leukocytes and lymphocytes.

Since this substance increases the amount of glutathione in the lungs, kidneys, liver and red bone marrow, it slows down the aging process, for example, by reducing the number of age spots. N-Acetylcysteine ​​is more effective at raising levels of glutathione in the body than cystine or even glutathione itself.

People with diabetes should be careful when taking cysteine ​​supplements as it has the ability to inactivate insulin. For cystinuria, a rare genetic condition that leads to the formation of cystine stones, cysteine ​​should not be taken.

Dimethylglycine

Dimethylglycine is a derivative of glycine, the simplest amino acid. It is a constituent of many important substances such as the amino acids methionine and choline, some hormones, neurotransmitters and DNA.

Dimethylglycine is found in small amounts in meats, seeds, and grains. Although there are no symptoms associated with dimethylglycine deficiency, dimethylglycine supplementation has a range of positive effects, including improving energy supply and mental performance.

Dimethylglycine also stimulates immunity, reduces cholesterol and triglycerides in the blood, helps normalize blood pressure and glucose levels, and helps normalize the function of many organs. It is also used for epileptic seizures.

Gamma-aminobutyric acid

Gamma-aminobutyric acid (GABA) functions in the body as a neurotransmitter of the central nervous system and is indispensable for the metabolism in the brain. It is formed from another amino acid - glutamine. It reduces the activity of neurons and prevents nerve cells from being overexcited.

Gamma-aminobutyric acid relieves anxiety and has a calming effect, it can be taken as tranquilizers, but without the risk of becoming addictive. This amino acid is used in the complex treatment of epilepsy and arterial hypertension. Since it has a relaxing effect, it is used in the treatment of sexual dysfunctions. In addition, GABA is prescribed for attention deficit disorder. Excess gamma-aminobutyric acid, however, can increase anxiety, shortness of breath, and tremors.

Glutamic acid

Glutamic acid is a neurotransmitter that transmits impulses in the central nervous system. This amino acid plays an important role in carbohydrate metabolism and promotes the penetration of calcium through the blood-brain barrier.

This amino acid can be used by brain cells as an energy source. It also detoxifies ammonia by removing nitrogen atoms during the formation of another amino acid, glutamine. This process is the only way to detoxify ammonia in the brain.

Glutamic acid is used in the correction of behavioral disorders in children, as well as in the treatment of epilepsy, muscular dystrophy, ulcers, hypoglycemic conditions, complications of insulin therapy for diabetes mellitus and mental development disorders.

Glutamine

Glutamine is the amino acid most commonly found in muscle in its free form. It very easily penetrates the blood-brain barrier and in the cells of the brain passes into glutamic acid and vice versa, in addition, it increases the amount of gamma-aminobutyric acid, which is necessary to maintain normal brain function.

This amino acid also maintains normal acid-base balance in the body and a healthy state of the gastrointestinal tract, it is necessary for the synthesis of DNA and RNA.

Glutamine is an active participant in nitrogen metabolism. Its molecule contains two nitrogen atoms and is formed from glutamic acid by the addition of one nitrogen atom. Thus, the synthesis of glutamine helps to remove excess ammonia from tissues, primarily from the brain, and transport nitrogen within the body.

Glutamine is found in large quantities in muscles and is used to synthesize proteins in skeletal muscle cells. Therefore, dietary supplements with glutamine are used by bodybuilders and for various diets, as well as for the prevention of muscle loss in diseases such as malignant neoplasms and AIDS, after surgery and with prolonged bed rest.

Additionally, glutamine is also used in the treatment of arthritis, autoimmune diseases, fibrosis, diseases of the gastrointestinal tract, peptic ulcers, and connective tissue diseases.

This amino acid improves brain activity and is therefore used in epilepsy, chronic fatigue syndrome, impotence, schizophrenia and senile dementia. L-glutamine reduces the pathological craving for alcohol, therefore it is used in the treatment of chronic alcoholism.

Glutamine is found in many foods, both plant and animal, but it is easily destroyed when heated. Spinach and parsley are good sources of glutamine, provided they are consumed raw.

Food supplements containing glutamine should only be stored in a dry place, otherwise glutamine is converted to ammonia and pyroglutamic acid. Do not take glutamine for liver cirrhosis, kidney disease, Reye's syndrome.

Glutathione

Glutathione, like carnitine, is not an amino acid. In terms of chemical structure, it is a tripeptide obtained in the body from cysteine, glutamic acid and glycine.

Glutathione is an antioxidant. Most glutathione is found in the liver (some of it is released directly into the bloodstream), as well as in the lungs and gastrointestinal tract.

It is essential for carbohydrate metabolism, and also slows down aging by affecting lipid metabolism and prevents the onset of atherosclerosis. Deficiency of glutathione affects primarily the nervous system, causing impaired coordination, thought processes, tremor.

The amount of glutathione in the body decreases with age. In this regard, older people should receive it additionally. However, it is preferable to consume food supplements containing cysteine, glutamic acid and glycine - that is, substances that synthesize glutathione. The most effective is the intake of N-acetylcysteine.

Glycine

Glycine slows down the degeneration of muscle tissue, as it is a source of creatine, a substance found in muscle tissue and used in the synthesis of DNA and RNA. Glycine is essential for the synthesis of nucleic acids, bile acids and nonessential amino acids in the body.

It is part of many antacids used for stomach diseases, it is useful for repairing damaged tissues, since it is found in large quantities in the skin and connective tissue.

This amino acid is essential for the normal functioning of the central nervous system and the maintenance of a good condition of the prostate gland. It acts as an inhibitory neurotransmitter and thus can prevent epileptic seizures.

Glycine is used in the treatment of manic-depressive psychosis and may also be effective for hyperactivity. An excess of glycine in the body makes you feel tired, but an adequate amount provides the body with energy. If necessary, glycine in the body can be converted to serine.

Histidine

Histidine is an essential amino acid that promotes tissue growth and repair, which is part of the myelin sheaths that protect nerve cells, and is also necessary for the formation of red and white blood cells. Histidine protects the body from the damaging effects of radiation, promotes the elimination of heavy metals from the body and helps with AIDS.

Too high levels of histidine can lead to stress and even mental disorders (agitation and psychosis).

An inadequate content of histidine in the body worsens the condition in rheumatoid arthritis and in deafness associated with damage to the auditory nerve. Methionine helps to lower the level of histidine in the body.

Histamine, a very important component of many immunological reactions, is synthesized from histidine. It also promotes sexual arousal. In this regard, the simultaneous intake of biologically active food supplements containing histidine, niacin and pyridoxine (necessary for the synthesis of histamine) may be effective in sexual dysfunctions.

Since histamine stimulates the secretion of gastric juice, the use of histidine helps with digestive disorders associated with low acidity of gastric juice.

People with manic-depressive psychosis should not take histidine unless a deficiency in this amino acid is well established. Histidine is found in rice, wheat, and rye.

Isoleucine

Isoleucine is one of the BCAA amino acids and essential amino acids required for the synthesis of hemoglobin. It also stabilizes and regulates blood sugar and energy supply processes. Isoleucine metabolism occurs in muscle tissue.

Co-administration with isoleucine and valine (BCAA) increases endurance and promotes muscle recovery, which is especially important for athletes.

Isoleucine is required for many mental illness... Deficiency of this amino acid leads to symptoms similar to hypoglycemia.

Food sources of isoleucine include almonds, cashews, chicken, chickpeas, eggs, fish, lentils, liver, meat, rye, most seeds, and soy proteins.

There are dietary supplements that contain isoleucine. In doing so, it is necessary to maintain the correct balance between isoleucine and the other two BCAA's, leucine and valine.

Leucine

Leucine is an essential amino acid that, together with isoleucine and valine, belong to the three branched chain amino acids of the BCAA. Working together, they protect muscle tissue and are sources of energy, as well as promote the restoration of bones, skin, muscles, so they are often recommended during the recovery period after injuries and surgeries.

Leucine also lowers blood sugar levels slightly and stimulates the release of growth hormone. Dietary sources of leucine include brown rice, beans, meat, nuts, soy flour, and wheat flour.

Biologically active food supplements containing leucine are used in combination with valine and isoleucine. They should be taken with care to avoid causing hypoglycemia. Excess leucine can increase the amount of ammonia in the body.

Lysine

Lysine is an essential amino acid found in almost any protein. It is essential for normal bone formation and growth in children, assists in the absorption of calcium and the maintenance of normal nitrogen metabolism in adults.

This amino acid is involved in the synthesis of antibodies, hormones, enzymes, collagen formation and tissue repair. Lysine is used in the recovery period after surgery and sports injuries. It also lowers serum triglyceride levels.

Lysine has antiviral effects, especially against viruses that cause herpes and acute respiratory infections. Taking supplements containing lysine in combination with vitamin C and bioflavonoids is recommended for viral illnesses.

Deficiency of this essential amino acid can lead to anemia, eyeball hemorrhages, enzyme disorders, irritability, fatigue and weakness, poor appetite, growth retardation and weight loss, and reproductive system disorders.

Dietary sources of lysine are cheese, eggs, fish, milk, potatoes, red meat, soy and yeast products.

Methionine

Methionine is an essential amino acid that aids in the processing of fats, preventing them from being deposited in the liver and on the walls of arteries. The synthesis of taurine and cysteine ​​depends on the amount of methionine in the body. This amino acid promotes digestion, provides detoxification processes (primarily neutralization of toxic metals), reduces muscle weakness, protects against radiation, is useful in osteoporosis and chemical allergies.

This amino acid is used in the complex therapy of rheumatoid arthritis and pregnancy toxicosis. Methionine has a pronounced antioxidant effect, as it is good source sulfur, which inactivates free radicals. It is used for Gilbert's syndrome, liver dysfunctions. Methionine is also required for the synthesis of nucleic acids, collagen, and many other proteins. It is useful for women receiving oral hormonal contraceptives. Methionine lowers the level of histamine in the body, which can be helpful in schizophrenia when the amount of histamine is high.

Methionine in the body is converted to cysteine, which is a precursor of glutathione. This is very important in case of poisoning, when a large amount of glutathione is required to neutralize toxins and protect the liver.

Dietary sources of methionine include legumes, eggs, garlic, lentils, meat, onions, soybeans, seeds, and yogurt.

Ornithine

Ornithine helps release growth hormone, which helps burn fat in the body. This effect is enhanced by the use of ornithine in combination with arginine and carnitine. Ornithine is also essential for the immune system and liver function, participating in detoxification processes and the restoration of liver cells.

Ornithine in the body is synthesized from arginine and, in turn, serves as a precursor for citrulline, proline, glutamic acid. High concentrations of ornithine are found in the skin and connective tissue, so this amino acid helps to repair damaged tissues.

Dietary supplements containing ornithine should not be given to children, pregnant and lactating mothers, or to people with a history of schizophrenia.

Phenylalanine

Phenylalanine is an essential amino acid. In the body, it can be converted into another amino acid, tyrosine, which, in turn, is used in the synthesis of two main neurotransmitters: dopamine and norepinephrine. Therefore, this amino acid affects mood, reduces pain, improves memory and learning ability, suppresses appetite. It is used in the treatment of arthritis, depression, menstrual pain, migraines, obesity, Parkinson's disease, and schizophrenia.

Phenylalanine occurs in three forms: L-phenylalanine ( natural shape and it is she who is part of most proteins human body), D-phenylalanine (synthetic mirror form, has an analgesic effect), DL-phenylalanine (combines the beneficial properties of the two previous forms, it is usually used for premenstrual syndrome.

Dietary supplements containing phenylalanine are not given to pregnant women, persons with anxiety attacks, diabetes, high blood pressure, phenylketonuria, pigment melanoma.

Proline

Proline improves skin condition by increasing collagen production and decreasing collagen loss with age. Helps in the restoration of the cartilaginous surfaces of the joints, strengthens the ligaments and heart muscle. To strengthen connective tissue, proline is best used in combination with vitamin C.

Proline enters the body primarily from meat products.

Serine

Serine is essential for the normal metabolism of fats and fatty acids, the growth of muscle tissue, and the maintenance of a normal immune system.

Serine is synthesized in the body from glycine. It is used as a moisturizing agent in many cosmetic and dermatological products.

Taurine

Taurine is found in high concentration in the heart muscle, white blood cells, skeletal muscles, and the central nervous system. It is involved in the synthesis of many other amino acids, and is also part of the main component of bile, which is necessary for the digestion of fats, the absorption of fat-soluble vitamins, and to maintain normal blood cholesterol levels.

Therefore, taurine is useful for atherosclerosis, edema, heart disease, arterial hypertension and hypoglycemia. Taurine is essential for the normal metabolism of sodium, potassium, calcium and magnesium. It prevents the excretion of potassium from the heart muscle and therefore helps prevent certain cardiac arrhythmias. Taurine has a protective effect on the brain, especially during dehydration. It is used in the treatment of anxiety and agitation, epilepsy, hyperactivity, seizures.

Taurine dietary supplements are given to children with Down syndrome and muscular dystrophy. In some clinics, this amino acid is included in the complex therapy of breast cancer. Excessive excretion of taurine from the body occurs in various conditions and metabolic disorders.

Arrhythmias, disorders of platelet formation, candidiasis, physical or emotional stress, bowel disease, zinc deficiency and alcohol abuse lead to a deficiency of taurine in the body. Alcohol abuse also interferes with the body's ability to absorb taurine.

With diabetes, the body's need for taurine increases, and vice versa, taking dietary supplements containing taurine and cystine reduces the need for insulin. Taurine is found in eggs, fish, meat, milk, but not in plant proteins.

It is synthesized in the liver from cysteine ​​and from methionine in other organs and tissues of the body, provided there is a sufficient amount of vitamin B6. In case of genetic or metabolic disorders that interfere with the synthesis of taurine, it is necessary to take a dietary supplement with this amino acid.

Threonine

Threonine is an essential amino acid that helps maintain normal protein metabolism in the body. It is important for the synthesis of collagen and elastin, helps the liver and participates in the metabolism of fats in combination with aspartic acid and methionine.

Threonine is found in the heart, central nervous system, skeletal muscles and inhibits the stored fat in the liver. This amino acid stimulates immunity by promoting the production of antibodies. Threonine is found in very small amounts in grains, so vegetarians are more likely to be deficient in this amino acid.

Tryptophan

Tryptophan is an essential amino acid essential for the production of niacin. It is used to synthesize serotonin in the brain, one of the most important neurotransmitters. Tryptophan is used for insomnia, depression and mood stabilization.

It helps with hyperactivity disorder in children, is used for heart disease, to control body weight, reduce appetite, and also to increase the release of growth hormone. Helps with migraine attacks, helps to reduce the harmful effects of nicotine. Tryptophan and magnesium deficiencies can worsen coronary artery spasms.

The richest dietary sources of tryptophan include brown rice, country cheese, meat, peanuts, and soy protein.

Tyrosine

Tyrosine is a precursor of the neurotransmitters norepinephrine and dopamine. This amino acid is involved in mood regulation; a lack of tyrosine leads to a deficiency of norepinephrine, which in turn leads to depression. Tyrosine suppresses appetite, helps reduce fat deposition, promotes melatonin production and improves adrenal, thyroid and pituitary function.

Tyrosine is also involved in the metabolism of phenylalanine. Thyroid hormones are formed when iodine atoms attach to tyrosine. Therefore, it is not surprising that low plasma tyrosine is associated with hypothyroidism.

Low blood pressure, low body temperature and restless legs syndrome are also symptoms of tyrosine deficiency.

Tyrosine dietary supplements are used to relieve stress and are believed to help with chronic fatigue syndrome and narcolepsy. They are used for anxiety, depression, allergies and headaches, as well as for drug withdrawal. Tyrosine may be beneficial for Parkinson's disease. Natural sources tyrosine - almonds, avocados, bananas, dairy products, pumpkin seeds, and sesame seeds.

Tyrosine can be synthesized from phenylalanine in the human body. Phenylalanine dietary supplements are best taken at bedtime or with foods that are high in carbohydrates.

Against the background of treatment with monoamine oxidase inhibitors (usually prescribed for depression), you should almost completely abandon foods containing tyrosine, and not take dietary supplements with tyrosine, as this can lead to an unexpected and sharp rise in blood pressure.

Valine

Valine is an essential stimulating amino acid, one of the BCAA amino acids, so it can be used by muscles as a source of energy. Valine is essential for muscle metabolism, repair of damaged tissue, and for the maintenance of normal nitrogen metabolism in the body.

Valine is often used to correct severe amino acid deficiencies resulting from drug addiction. Its excessively high level in the body can lead to symptoms such as paresthesia (a feeling of goose bumps on the skin), up to hallucinations.
Valine is found in the following foods: grains, meat, mushrooms, dairy products, peanuts, soy protein.

Valine supplementation should be balanced with other BCAAs L-Leucine and L-Isoleucine.