What are amino acids and what are their beneficial properties? Amino acids in bodybuilding Chemical names of amino acids

Amino acids are the main building material of any living organism. By their nature, they are the primary nitrogenous substances of plants, which are synthesized from the soil. The structure of amino acids depends on their composition.

Amino acid structure

Each of its molecules has carboxyl and amine groups, which are connected to a radical. If an amino acid contains 1 carboxyl and 1 amino group, its structure can be indicated by the formula presented below.

Amino acids that have 1 acid and 1 alkaline group are called monoaminomonocarboxylic acids. In organisms, 2 carboxyl groups or 2 amine groups are also synthesized and whose functions are determined. Amino acids containing 2 carboxyl and 1 amine groups are called monoaminodicarboxylic, and those containing 2 amine and 1 carboxyl are called diaminomonocarboxylic.

They also differ in the structure of the organic radical R. Each of them has its own name and structure. Hence the different functions of amino acids. It is the presence of acidic and alkaline groups that ensures its high reactivity. These groups connect amino acids and form a polymer - protein. Proteins are also called polypeptides because of their structure.

Amino acids as building materials

A protein molecule is a chain of tens or hundreds of amino acids. Proteins differ in composition, quantity and order of amino acids, because the number of combinations of 20 components is almost infinite. Some of them have the entire composition of essential amino acids, others do without one or more. Individual amino acids, a structure whose functions are similar to the proteins of the human body, are not used as food products, since they are poorly soluble and are not broken down by the gastrointestinal tract. These include the proteins of nails, hair, fur or feathers.

The functions of amino acids are difficult to overestimate. These substances are the main food in the human diet. What function do amino acids perform? They increase the growth of muscle mass, help strengthen joints and ligaments, restore damaged body tissues and participate in all processes occurring in the human body.

Essential amino acids

Only from supplements or food products can you get Functions in the process of forming healthy joints, strong muscles, beautiful hair are very significant. These amino acids include:

• phenylalanine;
• lysine;
• threonine;
• methionine;
• valine;
• leucine;
• tryptophan;
• histidine;
• isoleucine.

Functions of essential amino acids

These bricks perform essential functions in the functioning of every cell of the human body. They are invisible as long as they enter the body in sufficient quantities, but their deficiency significantly impairs the functioning of the entire body.

1. Valine renews muscles and serves as an excellent source of energy.
2. Histidine improves blood composition, promotes muscle recovery and growth, and improves joint function.
3. Isoleucine helps the production of hemoglobin. Controls the amount of sugar in the blood, increases a person’s energy and endurance.
4. Leucine strengthens the immune system, monitors the level of sugar and leukocytes in the blood. If the level of leukocytes is too high: it lowers them and activates the body’s reserves to eliminate inflammation.
5. Lysine helps absorb calcium, which builds and strengthens bones. Helps collagen production, improves hair structure. For men, this is an excellent anabolic steroid, as it builds muscles and increases male strength.
6. Methionine normalizes the functioning of the digestive system and liver. Participates in the breakdown of fats, eliminates toxicosis in pregnant women, and has a beneficial effect on hair.
7. Threonine improves the functioning of the gastrointestinal tract. Increases immunity, participates in the creation of elastin and collagen. Threonine prevents fat deposition in the liver.
8. Tryptophan is responsible for human emotions. Produces serotonin - the hormone of happiness, thereby normalizing sleep and elevating mood. Tames appetite, has a beneficial effect on the heart muscle and arteries.
9. Phenylalanine serves as a transmitter of signals from nerve cells to the brain of the head. Improves mood, suppresses unhealthy appetite, improves memory, increases sensitivity, reduces pain.

A deficiency of essential amino acids leads to stunted growth, metabolic disorders, and decreased muscle mass.

Nonessential amino acids

These are amino acids, the structure and functions of which are produced in the body:

• arginine;
• alanine;
• asparagine;
• glycine;
• proline;
• taurine;
• tyrosine;
• glutamate;
• serine;
• glutamine;
• ornithine;
• cysteine;
• carnitine

Functions of nonessential amino acids

1. Cysteine ​​eliminates toxic substances, participates in the creation of skin and muscle tissue, and is a natural antioxidant.
2. Tyrosine reduces physical fatigue, speeds up metabolism, eliminates stress and depression.
3. Alanine serves for muscle growth and is a source of energy.
4. increases metabolism and reduces ammonia formation during heavy exercise.
5. Cystine eliminates pain when ligaments and joints are injured.
6. responsible for brain activity, during prolonged physical activity it turns into glucose, producing energy.
7. Glutamine restores muscles, improves immunity, speeds up metabolism, enhances brain function and creates growth hormone.
8. Glycine is necessary for muscle function, fat breakdown, stabilization of blood pressure and blood sugar.
9. Carnitine moves fatty acids into cells, where they are broken down to release energy, resulting in the burning of excess fat and generating energy.
10. Ornithine produces growth hormone, is involved in the process of urine formation, breaks down fatty acids, and helps produce insulin.
11. Proline ensures the production of collagen, it is necessary for ligaments and joints.
12. Serine improves immunity and produces energy; it is needed for rapid metabolism of fatty acids and muscle growth.
13. Taurine breaks down fat, increases the body's resistance, and synthesizes bile salts.

Protein and its properties

Proteins, or proteins, are high-molecular compounds containing nitrogen. The concept of "protein", first designated by Berzelius in 1838, comes from the Greek word and means "primary", which reflects the leading role of proteins in nature. The variety of proteins makes it possible for a huge number of living beings to exist: from bacteria to the human body. There are significantly more of them than other macromolecules, because proteins are the foundation of a living cell. They make up approximately 20% of the mass of the human body, more than 50% of the dry mass of the cell. This number of diverse proteins is explained by the properties of twenty different amino acids, which interact with each other and create polymer molecules.

An outstanding property of proteins is the ability to independently create a certain spatial structure characteristic of a particular protein. Proteins are biopolymers with peptide bonds. The chemical composition of proteins is characterized by a constant average nitrogen content of approximately 16%.

Life, as well as the growth and development of the body, are impossible without the function of protein amino acids to build new cells. Proteins cannot be replaced by other elements; their role in the human body is extremely important.

Functions of proteins

The need for proteins lies in the following functions:

• it is necessary for growth and development, as it is the main building material for the creation of new cells;
• controls metabolism, during which energy is released. After eating food, the metabolic rate increases, for example, if the food consists of carbohydrates, the metabolism accelerates by 4%, if it consists of proteins - by 30%;
• regulate in the body due to its hydrophilicity - the ability to attract water;
• strengthen the immune system by synthesizing antibodies that protect against infection and eliminate the threat of disease.

Products - sources of proteins

The human muscles and skeleton consist of living tissues that not only function but are also renewed throughout life. They recover from damage and retain their strength and durability. To do this, they require very specific nutrients. Food provides the body with the energy it needs for all processes, including muscle function, tissue growth and repair. And protein in the body is used both as a source of energy and as a building material.

Therefore, it is very important to observe its daily use in food. Protein-rich foods: chicken, turkey, lean ham, pork, beef, fish, shrimp, beans, lentils, bacon, eggs, nuts. All these products provide the body with protein and provide the energy necessary for life.

To achieve good results in bodybuilding, an athlete must have a competent approach to nutrition and physical activity. Most modern athletes prefer sports nutrition, in particular taking amino acids. To choose the right amino acid supplements, you need to know what they are intended for and how to use them.

There are three types of amino acids: nonessential, conditionally essential and essential. Essential amino acids are not produced by the body on its own, so an athlete must add them to his diet.

Aminocarboxylic acids are one of the elements of protein. Their presence is of great importance for the normal functioning of the body, since they are necessary for the production of certain hormones, enzymes and antibodies.

Amino acid is the main element in the construction of all proteins in animal and plant organisms.

The importance of amino acids in bodybuilding

Since amino acids are involved in all body processes associated with physical activity (restoration and activation of muscle tissue growth, suppression of catabolic processes), it is difficult to overestimate their importance for modern athletes. The fact is that even moderate intensity physical activity leads to a significant consumption of free amino acids (up to 80%). And timely replenishment of the deficiency helps to build muscle mass and increase the effectiveness of training.
BCAAs (branched chain aminocarboxylic acids - valine, isoleucine and leucine) are of particular importance for bodybuilders, since almost 35% of all muscles consist of them. In addition, BCAAs have powerful anti-catabolic properties and other beneficial functions, and therefore many sports nutrition manufacturers make nutritional supplements based on them.

BCAA is three essential amino acids: leucine, isoleucine and valine, the starting material for the construction and regeneration of body cells.

Types of amino acids

Amino acid complexes differ in composition, amino acid ratio and degree of hydrolysis. Amino acids in free form, usually isolated, we have already mentioned, are glutamine, arginine, glycine, etc., but complexes also occur. Hydrolysates are broken down proteins that contain short amino acid chains that can be quickly absorbed. Di- and tripeptide forms are essentially also hydrolysates, only the chains of amino acids are shorter, and consist of 2 and 3 amino acids, respectively, and are absorbed very quickly. BCAA is a complex of three amino acids - leucine, isoleucine and valine, which are most in demand in muscles and are absorbed very quickly.

Amino acids are available in the form of powder, tablets, solutions, capsules, but all these forms are equivalent in effectiveness. There are also injectable forms of amino acids that are administered intravenously. It is not recommended to use amino acids by injection, as this does not have any advantages over oral administration, but there is a high risk of complications and adverse reactions.

One of the most common forms of amino acid release is tablets and capsules.

Classification of amino acids

There is the following classification of aminocarboxylic acids:

1. Replaceable. These amino acid compounds can be synthesized independently, especially after taking enzymes, minerals and vitamins. Non-essential amino acids include: glutamine, arginine, taurine, asparagine, glycine, carnitine and others.
2. Partially replaceable (or conditionally irreplaceable). Synthesized in the body in limited quantities, these include tyrosine, alanine, histidine and cysteine.
3. Irreplaceable. They are not produced by the body and come only from food and sports supplements, and therefore their deficiency is often observed.

A person receives this type of acids (EAA) only from food. Their deficiency in the body leads to deterioration of health, metabolic disorders, and decreased immunity.

At the same time, the need for EAA can be met only with the help of an abundant and balanced diet, which is practically impossible.
This is why many bodybuilders choose to obtain essential amino acids through regular supplementation. To stimulate protein synthesis and muscle growth, it is recommended to take such drugs both before and after training.

Valine, methionine, tryptophan are part of the drugs that contain essential amino acids.

List of essential amino acids

It includes several EAAs:

1. Valin. Takes part in the formation of glycogen and stimulates energy production during a low-calorie diet.
2. Isoleucine. Breaks down cholesterol and is necessary for the formation of hemoglobin and glycogen, as well as the metabolism of carbohydrates.
3. Leucine. Reduces blood sugar levels in diabetes, fills the body with energy, takes part in the metabolism of carbohydrates and activates the breakdown of cholesterol.
4. Lysine. When metabolized in combination with methionine and vitamin C, it forms carnitine, which improves the body's resistance to stress and fatigue. It also stimulates mental activity, supports high performance of the immune system, has a positive effect on calcium absorption and the restoration of connective and bone tissues.
5. Methionine. It is a powerful antioxidant, activates the process of regeneration of kidney and liver tissue, has a lipotropic effect, takes part in the formation of creatine, cysteine, adrenaline and choline.
6. Threonine. Necessary for the formation of elastin and collagen, tissue growth, isoleucine biosynthesis and activation of the immune system. Promotes the process of energy exchange in muscle cells.
7. Tryptophan. A kind of antidepressant. In combination with vitamin B6 and biotin, it helps normalize sleep. It also takes part in the formation of serotonin and nicotinic acid, and stimulates an increase in the level of growth hormone in the blood.
8. Phenylalanine (CNS stimulant). Required for the production of collagen and neurotransmitters, participates in the formation of triiodothyronine, thyroxine, dopamine, norepinephrine, adrenaline, melanin, insulin. It has a beneficial effect on the functioning of the circulatory system, helps reduce appetite and improve mood, attention, memory and performance.

Since essential amines cannot be synthesized in the body, they are all needed by the body. However, the most important for athletes are the branched chain amines, also known as BCAA. This group includes three substances: isoleucine, valine, leucine.

The name of these substances is related to their molecular structure, which contains an additional carbohydrate chain. These are unique amines because they are metabolized in muscle tissue, while other amino acid compounds are processed in the liver. Now it is quite clear why BCAAs are often called muscle amines.
Among the amines of the BCAA group, leucine has the greatest anabolic properties. Today, BCAA can be purchased as a separate supplement, and these substances are also included in a large number of other supplements, for example, mass gainers, pre-workout complexes, etc.

BCAAs

BCAAs have a wide range of positive effects, which we will now discuss.

The use of these amino acids stimulates the formation of new muscle tissue, accelerates recovery and slows down the process of destruction of existing muscle tissue, normalizes fat metabolism processes, accelerates fat burning and improves metabolism.

• Anti-catabolic effect

Amines of the BCAA group can effectively protect muscles from destruction. This property of substances is actively used by bodybuilders during cutting, when they have to be on a low-carbohydrate diet program.

During training, the body's glycogen reserves are consumed quite quickly and protein compounds that make up muscle tissue begin to be used to obtain energy.
Since during drying the amount of carbohydrates is limited, the energy reserves in the body are small. This can lead to serious weight loss. However, we note that the less fat mass in your body, the higher the likelihood of losing muscle tissue. If you use BCAAs before a cardio session, this can be avoided.

• Increases the effectiveness of training

Many novice athletes are interested in whether BCAA can increase the effectiveness of training. To answer this question, here are the results of one study. The experiment participants were divided into two groups. Representatives of the first took a placebo, and the second used BCAAs. The training process was the same in each group.
As a result, scientists stated that when consuming amines, the rate of secretion of cortisol and a special enzyme that can destroy muscle tissue, creatine kinase, decreased. At the same time, an increase in the concentration of the male hormone was recorded. It should also be said that subjects with large fat mass consumed amines in larger quantities in order for the anabolic effect of the supplement to manifest itself.

• Stimulation of the production of anabolic hormonal substances

The group of anabolic hormones includes somatotropin, insulin and testosterone. All of them are able to resist the destructive effects of cortisol on the body. Numerous studies have shown that BCAA can speed up the production of all these substances.
This fact also explains the strong anti-catabolic properties of amines of the BCAA group. For example, leucine has the ability to enhance the work of insulin, which leads to accelerated production of protein compounds in muscle tissue. There are also research results that indicate the positive effects of leucine in relation to the processes of reduction of adipose tissue. We also note that the effectiveness of supplements with amines from the BCAA group can be enhanced with the help of vitamin B1.

Glutamine

Glutamine is a conditionally essential amino acid that is part of protein and is necessary for effective muscle growth and support of the immune system. Glutamine is very common in nature and is a conditionally essential amino acid for humans. Glutamine circulates in fairly large quantities in the blood and accumulates in the muscles. Glutamine is the most abundant amino acid in the body, and muscles consist of 60% of it, this once again emphasizes its importance in bodybuilding.

Glutamine is required for efficient and productive growth of muscle tissue. This amino acid is found in abundance in muscle cells and circulates in the blood.

Effects of Glutamine

• Participates in the synthesis of muscle proteins.
• It is a source of energy, along with glucose.
• It has an anti-catabolic effect (suppresses the secretion of cortisol).
• Causes an increase in the level of growth hormone (when consuming 5 g daily, the level of GH increases 4 times).
• Strengthens the immune system.
• Accelerates recovery after training and prevents the development of overtraining.

How to take glutamine?

Recommended doses of glutamine are 4-8 g per day. It is optimal to divide this dose into two doses: immediately after training and before bed on an empty stomach. After training, glutamine quickly replenishes the depleted pool, suppresses catabolism and triggers muscle growth. It is recommended to take glutamine before bed because growth hormone is produced at night, and glutamine can enhance this process. On rest days, take glutamine at lunch and before bed on an empty stomach.

Combination of glutamine with sports nutrition

Glutamine combines well with many sports supplements, and the effects mutually enhance. The most optimal combination: glutamine + creatine, protein. This bundle can include pre-workout complexes, anabolic complexes (testosterone boosters) and other supplements. Do not mix glutamine and protein together as this will reduce the rate of absorption of the former, but take them at least 30 minutes apart. Creatine and glutamine can be mixed and taken at the same time.

Side effects

Glutamine is a naturally occurring amino acid that is constantly supplied through food. Supplemental glutamine intake is not harmful to health and generally does not cause any side effects.

Other amino acids common in bodybuilding

• Arginine - improved muscle nutrition, nutrient transport, pumping.
• L-carnitine is one of the best fat burners that is absolutely safe for health.
• Beta Alanine - Muscle Antioxidant and Regenerator
• Citrulline is a powerful energy restorer after training, prevents overtraining, and improves muscle nutrition.

Amino acids from the pharmacy

Modern medicine attaches great importance to drugs based on amino acids. All biochemical systems of the body consist of these compounds, and this necessitates the need for their production (you can purchase most amino acids at the pharmacy).

The main purpose of amino acids is the synthesis of enzymes, which are natural accelerators of all chemical reactions in the body. The better and more efficiently the processes of protein synthesis occur, the more energy a person releases.

It is estimated that the action of amino acids in the bodies of athletes provides about 10% of their total energy. If the muscles have exhausted their energy reserves during training, then in order to restore physical performance and progress, it is necessary to consume a significant amount of amino acids.
Some of the amino acids can influence the production of growth hormones, which makes them useful for athletes involved in strength sports. This fact was proven during the experiment: after taking L-arginine and L-ornithine, the subjects experienced a short-term but quite significant natural increase in growth hormone levels.
A strength program was written for twenty-two participants in the experiment, which lasted five weeks. One group had a certain amount of L-arginine added to their diet, while the other group took a placebo (a substance with weak chemical and anabolic activity). After completing the course of training, strength and muscle gains of all trainees were measured. The results showed that athletes who took amino acids had significantly greater gains.

Phenylalanine

One of the most valuable amino acids for the body is phenylalanine. It has an important effect on the body. One of its functions is to protect endorphins. These cells control pain in the body, and the presence of D- and L-phenylalanine helps relieve acute pain in the long term. This amino acid is produced naturally in the body and is a thousand times more potent than morphine. Taking a small amount of phenylalanine has a good pain-relieving effect.

Glycine

An equally valuable amino acid from the pharmacy is Glycine - an amino acid that does not have optical isomers, which is part of many proteins and various biological compounds. It is recommended to be used for diseases of the central nervous system, prolonged stress, insomnia, increased excitability, heavy physical exertion, and ischemic stroke. It is recommended to consume 0.3 g per day for a month. If necessary, the course can be repeated.

Action of glycine

• Your mood improves.
• Aggression decreases.
• Sleep is normalized.
• Mental performance increases.
• The nervous system receives additional protection from the effects of alcohol and other harmful substances.

Glycine can be found in any pharmacy, the average price is 50 rubles. per package. Many people take glycine to stimulate brain activity; this pharmaceutical amino acid is very popular among athletes.

Methionine

Methionine is an essential amino acid that is part of proteins; it also:

• lowers blood cholesterol levels
• used as an antidepressant
• improves liver function

Methionine is found in large quantities in meat (beef and chicken), and also in cottage cheese, eggs, wheat, rice, oatmeal, pearl barley, buckwheat, and pasta. Not much of it is found in bananas, soybeans, and beans. It is recommended to take it 0.5g three times a day. This pharmaceutical amino acid is usually prescribed for liver diseases or protein deficiency. Use is contraindicated if you have severe sensitivity to methionine. Cost in pharmacies – 100 rubles. per pack.

Glutamine

60% of the amino acids inside muscles are glutamine, it performs many different functions in the body, so taking it in the form of a supplement definitely won’t hurt.

Glutamine is an essential amino acid that you can purchase at the pharmacy; it is part of proteins and is necessary for proper muscle growth and maintaining immunity. The cost of glutamine is much higher than glycine, but it may be cheaper to buy it at a pharmacy than to buy it at a sports nutrition store. It is recommended to take glutamine 5 g 2 times a day.
Action of glutamine

• Is a source of energy.
• It is anti-catabolic protection.
• Helps strengthen the immune system.
• Improves the quality of restoration processes.
• Stimulates muscle growth.

Among the variety of amino acids, only 20 are involved in intracellular protein synthesis ( proteinogenic amino acids). Also, about 40 more non-proteinogenic amino acids have been found in the human body. All proteinogenic amino acids are α- amino acids and their example can be shown additional ways classifications.

According to the structure of the side radical

Highlight

• aliphatic(alanine, valine, leucine, isoleucine, proline, glycine),
• aromatic(phenylalanine, tyrosine, tryptophan),
• sulfur-containing(cysteine, methionine),
• containing OH group(serine, threonine, tyrosine again),
• containing additional COOH group(aspartic and glutamic acids),
• additional NH 2 group(lysine, arginine, histidine, also glutamine, asparagine).

Usually the names of amino acids are abbreviated to a 3-letter designation. Molecular biology professionals also use single-letter symbols for each amino acid.

Structure of proteinogenic amino acids

According to the polarity of the side radical

Exist non-polar amino acids (aromatic, aliphatic) and polar(uncharged, negatively and positively charged).

According to acid-base properties

According to their acid-base properties they are divided into neutral(majority), sour(aspartic and glutamic acids) and basic(lysine, arginine, histidine) amino acids.

By irreplaceability

According to the need for the body, those that are not synthesized in the body and must be supplied with food are isolated - irreplaceable amino acids (leucine, isoleucine, valine, phenylalanine, tryptophan, threonine, lysine, methionine). TO replaceable include those amino acids whose carbon skeleton is formed in metabolic reactions and is capable of somehow obtaining an amino group to form the corresponding amino acid. The two amino acids are conditionally irreplaceable (arginine, histidine), i.e. their synthesis occurs in insufficient quantities, especially for children.

Proteins form the material basis of the chemical activity of the cell. The functions of proteins in nature are universal. Name proteins, the most accepted term in Russian literature corresponds to the term proteins(from Greek proteios- first). To date, great strides have been made in establishing the relationship between the structure and functions of proteins, the mechanism of their participation in the most important processes of the body's life, and in understanding the molecular basis of the pathogenesis of many diseases.

Depending on their molecular weight, peptides and proteins are distinguished. Peptides have a lower molecular weight than proteins. Peptides are more likely to have a regulatory function (hormones, enzyme inhibitors and activators, ion transporters across membranes, antibiotics, toxins, etc.).

12.1. α -Amino acids

12.1.1. Classification

Peptides and proteins are built from α-amino acid residues. The total number of naturally occurring amino acids exceeds 100, but some of them are found only in a certain community of organisms; the 20 most important α-amino acids are constantly found in all proteins (Scheme 12.1).

α-Amino acids are heterofunctional compounds whose molecules contain both an amino group and a carboxyl group at the same carbon atom.

Scheme 12.1.The most important α-amino acids*

* Abbreviations are used only to write amino acid residues in peptide and protein molecules. ** Essential amino acids.

The names of α-amino acids can be constructed using substitutive nomenclature, but their trivial names are more often used.

Trivial names for α-amino acids are usually associated with sources of isolation. Serine is part of silk fibroin (from lat. serieus- silky); Tyrosine was first isolated from cheese (from the Greek. tyros- cheese); glutamine - from cereal gluten (from German. Gluten- glue); aspartic acid - from asparagus sprouts (from lat. asparagus- asparagus).

Many α-amino acids are synthesized in the body. Some amino acids necessary for protein synthesis are not produced in the body and must come from outside. These amino acids are called irreplaceable(see diagram 12.1).

Essential α-amino acids include:

valine isoleucine methionine tryptophan

leucine lysine threonine phenylalanine

α-Amino acids are classified in several ways depending on the characteristic that serves as the basis for their division into groups.

One of the classification features is the chemical nature of the radical R. Based on this feature, amino acids are divided into aliphatic, aromatic and heterocyclic (see diagram 12.1).

Aliphaticα -amino acids. This is the largest group. Within it, amino acids are divided using additional classification features.

Depending on the number of carboxyl groups and amino groups in the molecule, the following are distinguished:

Neutral amino acids - one NH group each 2 and COOH;

Basic amino acids - two NH groups 2 and one group

COOH;

Acidic amino acids - one NH 2 group and two COOH groups.

It can be noted that in the group of aliphatic neutral amino acids the number of carbon atoms in the chain does not exceed six. At the same time, there are no amino acids with four carbon atoms in the chain, and amino acids with five and six carbon atoms have only a branched structure (valine, leucine, isoleucine).

An aliphatic radical may contain “additional” functional groups:

Hydroxyl - serine, threonine;

Carboxylic - aspartic and glutamic acids;

Thiol - cysteine;

Amide - asparagine, glutamine.

Aromaticα -amino acids. This group includes phenylalanine and tyrosine, constructed in such a way that the benzene rings in them are separated from the common α-amino acid fragment by the methylene group -CH 2-.

Heterocyclic α -amino acids. Histidine and tryptophan belonging to this group contain heterocycles - imidazole and indole, respectively. The structure and properties of these heterocycles are discussed below (see 13.3.1; 13.3.2). The general principle of constructing heterocyclic amino acids is the same as aromatic ones.

Heterocyclic and aromatic α-amino acids can be considered as β-substituted derivatives of alanine.

The amino acid also belongs to gerocyclic proline, in which the secondary amino group is included in the pyrrolidine

In the chemistry of α-amino acids, much attention is paid to the structure and properties of the “side” radicals R, which play an important role in the formation of the structure of proteins and the performance of their biological functions. Of great importance are such characteristics as the polarity of the “side” radicals, the presence of functional groups in the radicals and the ability of these functional groups to ionize.

Depending on the side radical, amino acids with non-polar(hydrophobic) radicals and amino acids c polar(hydrophilic) radicals.

The first group includes amino acids with aliphatic side radicals - alanine, valine, leucine, isoleucine, methionine - and aromatic side radicals - phenylalanine, tryptophan.

The second group includes amino acids that have polar functional groups in their radicals that are capable of ionization (ionogenic) or are unable to transform into an ionic state (nonionic) under body conditions. For example, in tyrosine the hydroxyl group is ionic (phenolic in nature), in serine it is nonionic (alcoholic in nature).

Polar amino acids with ionic groups in radicals under certain conditions can be in an ionic (anionic or cationic) state.

12.1.2. Stereoisomerism

The main type of construction of α-amino acids, i.e., the bond of the same carbon atom with two different functional groups, a radical and a hydrogen atom, in itself predetermines the chirality of the α-carbon atom. The exception is the simplest amino acid glycine H 2 NCH 2 COOH, which has no center of chirality.

The configuration of α-amino acids is determined by the configuration standard - glyceraldehyde. The location of the amino group in the standard Fischer projection formula on the left (similar to the OH group in l-glyceraldehyde) corresponds to the l-configuration, and on the right - to the d-configuration of the chiral carbon atom. By R, In the S-system, the α-carbon atom in all α-amino acids of the l-series has an S-configuration, and in the d-series, an R-configuration (the exception is cysteine, see 7.1.2).

Most α-amino acids contain one asymmetric carbon atom per molecule and exist as two optically active enantiomers and one optically inactive racemate. Almost all natural α-amino acids belong to the l-series.

The amino acids isoleucine, threonine and 4-hydroxyproline contain two chirality centers in the molecule.

Such amino acids can exist as four stereoisomers, representing two pairs of enantiomers, each of which forms a racemate. To build animal proteins, only one of the enantiomers is used.

The stereoisomerism of isoleucine is similar to the previously discussed stereoisomerism of threonine (see 7.1.3). Of the four stereoisomers, proteins contain l-isoleucine with the S configuration of both asymmetric carbon atoms C-α and C-β. The names of another pair of enantiomers that are diastereomers with respect to leucine use the prefix Hello-.

Cleavage of racemates. The source of α-amino acids of the l-series are proteins, which are subjected to hydrolytic cleavage for this purpose. Due to the great need for individual enantiomers (for the synthesis of proteins, medicinal substances, etc.) chemical methods for breaking down synthetic racemic amino acids. Preferred enzymatic method of digestion using enzymes. Currently, chromatography on chiral sorbents is used to separate racemic mixtures.

12.1.3. Acid-base properties

The amphotericity of amino acids is determined by acidic (COOH) and basic (NH 2) functional groups in their molecules. Amino acids form salts with both alkalis and acids.

In the crystalline state, α-amino acids exist as dipolar ions H3N+ - CHR-COO- (commonly used notation

The structure of the amino acid in non-ionized form is for convenience only).

In aqueous solution, amino acids exist in the form of an equilibrium mixture of dipolar ion, cationic and anionic forms.

The equilibrium position depends on the pH of the medium. For all amino acids, cationic forms predominate in strongly acidic (pH 1-2) and anionic forms in strongly alkaline (pH > 11) environments.

The ionic structure determines a number of specific properties of amino acids: high melting point (above 200? C), solubility in water and insolubility in non-polar organic solvents. The ability of most amino acids to dissolve well in water is an important factor in ensuring their biological functioning; the absorption of amino acids, their transport in the body, etc. are associated with it.

A fully protonated amino acid (cationic form), from the standpoint of Brønsted’s theory, is a dibasic acid,

By donating one proton, such a dibasic acid turns into a weak monobasic acid - a dipolar ion with one acid group NH 3 + . Deprotonation of the dipolar ion leads to the production of the anionic form of the amino acid - the carboxylate ion, which is a Brønsted base. The values ​​characterize

The basic acidic properties of the carboxyl group of amino acids usually range from 1 to 3; values pK a2 characterizing the acidity of the ammonium group - from 9 to 10 (Table 12.1).

Table 12.1.Acid-base properties of the most important α-amino acids

The equilibrium position, i.e., the ratio of different forms of an amino acid, in an aqueous solution at certain pH values ​​significantly depends on the structure of the radical, mainly on the presence of ionic groups in it, playing the role of additional acidic and basic centers.

The pH value at which the concentration of dipolar ions is maximum, and the minimum concentrations of cationic and anionic forms of an amino acid are equal, is calledisoelectric point (p/).

Neutralα -amino acids. These amino acids matterpIslightly lower than 7 (5.5-6.3) due to the greater ability to ionize the carboxyl group under the influence of the -/- effect of the NH 2 group. For example, alanine has an isoelectric point at pH 6.0.

Sourα -amino acids. These amino acids have an additional carboxyl group in the radical and are in a fully protonated form in a strongly acidic environment. Acidic amino acids are tribasic (according to Brøndsted) with three meaningspK a,as can be seen in the example of aspartic acid (p/ 3.0).

For acidic amino acids (aspartic and glutamic), the isoelectric point is at a pH much lower than 7 (see Table 12.1). In the body at physiological pH values ​​(for example, blood pH 7.3-7.5), these acids are in anionic form, since both carboxyl groups are ionized.

Basicα -amino acids. In the case of basic amino acids, the isoelectric points are located in the pH region above 7. In a strongly acidic environment, these compounds are also tribasic acids, the ionization stages of which are illustrated by the example of lysine (p/ 9.8).

In the body, basic amino acids are found in the form of cations, that is, both amino groups are protonated.

In general, no α-amino acid in vivois not at its isoelectric point and does not fall into a state corresponding to the lowest solubility in water. All amino acids in the body are in ionic form.

12.1.4. Analytically important reactions α -amino acids

α-Amino acids, as heterofunctional compounds, enter into reactions characteristic of both the carboxyl and amino groups. Some chemical properties of amino acids are due to the functional groups in the radical. This section discusses reactions that are of practical importance for the identification and analysis of amino acids.

Esterification.When amino acids react with alcohols in the presence of an acid catalyst (for example, hydrogen chloride gas), esters are obtained in the form of hydrochlorides in good yield. To isolate free esters, the reaction mixture is treated with ammonia gas.

Amino acid esters do not have a dipolar structure, therefore, unlike the parent acids, they dissolve in organic solvents and are volatile. Thus, glycine is a crystalline substance with a high melting point (292°C), and its methyl ester is a liquid with a boiling point of 130°C. Analysis of amino acid esters can be carried out using gas-liquid chromatography.

Reaction with formaldehyde. Of practical importance is the reaction with formaldehyde, which underlies the quantitative determination of amino acids by the method formol titration(Sørensen method).

The amphoteric nature of amino acids does not allow direct titration with alkali for analytical purposes. The interaction of amino acids with formaldehyde produces relatively stable amino alcohols (see 5.3) - N-hydroxymethyl derivatives, the free carboxyl group of which is then titrated with alkali.

Qualitative reactions. A feature of the chemistry of amino acids and proteins is the use of numerous qualitative (color) reactions, which previously formed the basis of chemical analysis. Nowadays, when research is carried out using physicochemical methods, many qualitative reactions continue to be used for the detection of α-amino acids, for example, in chromatographic analysis.

Chelation. With cations of heavy metals, α-amino acids as bifunctional compounds form intra-complex salts, for example, with freshly prepared copper(11) hydroxide under mild conditions, well-crystallizing chelates are obtained

blue copper(11) salts (one of the nonspecific methods for detecting α-amino acids).

Ninhydrin reaction. The general qualitative reaction of α-amino acids is the reaction with ninhydrin. The reaction product has a blue-violet color, which is used for visual detection of amino acids on chromatograms (on paper, in a thin layer), as well as for spectrophotometric determination on amino acid analyzers (the product absorbs light in the region of 550-570 nm).

Deamination. In laboratory conditions, this reaction is carried out by the action of nitrous acid on α-amino acids (see 4.3). In this case, the corresponding α-hydroxy acid is formed and nitrogen gas is released, the volume of which is used to determine the amount of amino acid that has reacted (Van-Slyke method).

Xanthoprotein reaction. This reaction is used to detect aromatic and heterocyclic amino acids - phenylalanine, tyrosine, histidine, tryptophan. For example, when concentrated nitric acid acts on tyrosine, a nitro derivative is formed, colored yellow. In an alkaline environment, the color becomes orange due to ionization of the phenolic hydroxyl group and an increase in the contribution of the anion to conjugation.

There are also a number of private reactions that allow the detection of individual amino acids.

Tryptophan detected by reaction with p-(dimethylamino)benzaldehyde in sulfuric acid by the appearance of a red-violet color (Ehrlich reaction). This reaction is used for the quantitative analysis of tryptophan in protein breakdown products.

Cysteine detected through several qualitative reactions based on the reactivity of the mercapto group it contains. For example, when a protein solution with lead acetate (CH3COO)2Pb is heated in an alkaline medium, a black precipitate of lead sulfide PbS is formed, which indicates the presence of cysteine ​​in proteins.

12.1.5. Biologically important chemical reactions

In the body, under the influence of various enzymes, a number of important chemical transformations of amino acids are carried out. Such transformations include transamination, decarboxylation, elimination, aldol cleavage, oxidative deamination, and oxidation of thiol groups.

Transamination is the main pathway for the biosynthesis of α-amino acids from α-oxoacids. The donor of the amino group is an amino acid present in cells in sufficient quantity or excess, and its acceptor is an α-oxoacid. In this case, the amino acid is converted into an oxoacid, and the oxoacid into an amino acid with the corresponding structure of radicals. As a result, transamination is a reversible process of interchange of amino and oxo groups. An example of such a reaction is the production of l-glutamic acid from 2-oxoglutaric acid. The donor amino acid can be, for example, l-aspartic acid.

α-Amino acids contain an electron-withdrawing amino group (more precisely, a protonated amino group NH) in the α-position to the carboxyl group 3 +), and therefore capable of decarboxylation.

Eliminationcharacteristic of amino acids in which the side radical in the β-position to the carboxyl group contains an electron-withdrawing functional group, for example, hydroxyl or thiol. Their elimination leads to intermediate reactive α-enamino acids, which easily transform into tautomeric imino acids (analogy with keto-enol tautomerism). As a result of hydration at the C=N bond and subsequent elimination of the ammonia molecule, α-imino acids are converted into α-oxo acids.

This type of transformation is called elimination-hydration. An example is the production of pyruvic acid from serine.

Aldol cleavage occurs in the case of α-amino acids, which contain a hydroxyl group in the β-position. For example, serine is broken down to form glycine and formaldehyde (the latter is not released in free form, but immediately binds to the coenzyme).

Oxidative deamination can be carried out with the participation of enzymes and the coenzyme NAD+ or NADP+ (see 14.3). α-Amino acids can be converted into α-oxoacids not only through transamination, but also through oxidative deamination. For example, α-oxoglutaric acid is formed from l-glutamic acid. At the first stage of the reaction, glutamic acid is dehydrogenated (oxidized) to α-iminoglutaric acid

acids. In the second stage, hydrolysis occurs, resulting in α-oxoglutaric acid and ammonia. The hydrolysis stage occurs without the participation of an enzyme.

The reaction of reductive amination of α-oxo acids occurs in the opposite direction. α-oxoglutaric acid, always contained in cells (as a product of carbohydrate metabolism), is converted in this way into L-glutamic acid.

Oxidation of thiol groups underlies the interconversions of cysteine ​​and cystine residues, providing a number of redox processes in the cell. Cysteine, like all thiols (see 4.1.2), is easily oxidized to form a disulfide, cystine. The disulfide bond in cystine is easily reduced to form cysteine.

Due to the ability of the thiol group to easily oxidize, cysteine ​​performs a protective function when the body is exposed to substances with high oxidative capacity. In addition, it was the first drug to show anti-radiation effects. Cysteine ​​is used in pharmaceutical practice as a stabilizer for drugs.

Conversion of cysteine ​​to cystine results in the formation of disulfide bonds, such as in reduced glutathione

(see 12.2.3).

12.2. Primary structure of peptides and proteins

Conventionally, it is believed that peptides contain up to 100 amino acid residues in a molecule (which corresponds to a molecular weight of up to 10 thousand), and proteins contain more than 100 amino acid residues (molecular weight from 10 thousand to several million).

In turn, in the group of peptides it is customary to distinguish oligopeptides(low molecular weight peptides) containing no more than 10 amino acid residues in the chain, and polypeptides, the chain of which includes up to 100 amino acid residues. Macromolecules with a number of amino acid residues approaching or slightly exceeding 100 do not distinguish between polypeptides and proteins; these terms are often used as synonyms.

A peptide and protein molecule can be formally represented as a product of polycondensation of α-amino acids, which occurs with the formation of a peptide (amide) bond between monomer units (Scheme 12.2).

The design of the polyamide chain is the same for the entire variety of peptides and proteins. This chain has an unbranched structure and consists of alternating peptide (amide) groups -CO-NH- and fragments -CH(R)-.

One end of the chain containing an amino acid with a free NH group 2, is called the N-terminus, the other is called the C-terminus,

Scheme 12.2.The principle of constructing a peptide chain

which contains an amino acid with a free COOH group. Peptide and protein chains are written from the N-terminus.

12.2.1. Structure of the peptide group

In the peptide (amide) group -CO-NH- the carbon atom is in a state of sp2 hybridization. The lone pair of electrons of the nitrogen atom enters into conjugation with the π-electrons of the C=O double bond. From the standpoint of electronic structure, the peptide group is a three-center p,π-conjugated system (see 2.3.1), the electron density in which is shifted towards the more electronegative oxygen atom. The C, O, and N atoms forming a conjugated system are located in the same plane. The electron density distribution in the amide group can be represented using the boundary structures (I) and (II) or the electron density shift as a result of the +M- and -M-effects of the NH and C=O groups, respectively (III).

As a result of conjugation, some alignment of bond lengths occurs. The C=O double bond is extended to 0.124 nm compared to the usual length of 0.121 nm, and the C-N bond becomes shorter - 0.132 nm compared to 0.147 nm in the usual case (Fig. 12.1). The planar conjugated system in the peptide group causes difficulty in rotation around the C-N bond (the rotation barrier is 63-84 kJ/mol). Thus, the electronic structure determines a fairly rigid flat structure of the peptide group.

As can be seen from Fig. 12.1, the α-carbon atoms of amino acid residues are located in the plane of the peptide group on opposite sides of the C-N bond, i.e., in a more favorable trans position: the side radicals R of amino acid residues in this case will be the most distant from each other in space.

The polypeptide chain has a surprisingly uniform structure and can be represented as a series of each other located at an angle.

Rice. 12.1.Planar arrangement of the peptide group -CO-NH- and α-carbon atoms of amino acid residues

to each other planes of peptide groups connected to each other through α-carbon atoms by Cα-N and Cα-Csp bonds 2 (Fig. 12.2). Rotation around these single bonds is very limited due to difficulties in the spatial placement of side radicals of amino acid residues. Thus, the electronic and spatial structure of the peptide group largely determines the structure of the polypeptide chain as a whole.

Rice. 12.2.The relative position of the planes of peptide groups in the polypeptide chain

12.2.2. Composition and amino acid sequence

With a uniformly constructed polyamide chain, the specificity of peptides and proteins is determined by two most important characteristics - amino acid composition and amino acid sequence.

The amino acid composition of peptides and proteins is the nature and quantitative ratio of their α-amino acids.

The amino acid composition is determined by analyzing peptide and protein hydrolysates, mainly by chromatographic methods. Currently, such analysis is carried out using amino acid analyzers.

Amide bonds are capable of hydrolysis in both acidic and alkaline environments (see 8.3.3). Peptides and proteins are hydrolyzed to form either shorter chains - this is the so-called partial hydrolysis, or a mixture of amino acids (in ionic form) - complete hydrolysis. Hydrolysis is usually carried out in an acidic environment, since many amino acids are unstable under alkaline hydrolysis conditions. It should be noted that the amide groups of asparagine and glutamine are also subject to hydrolysis.

The primary structure of peptides and proteins is the amino acid sequence, i.e. the order of alternation of α-amino acid residues.

The primary structure is determined by sequentially removing amino acids from either end of the chain and identifying them.

12.2.3. Structure and nomenclature of peptides

Peptide names are constructed by sequentially listing amino acid residues, starting from the N-terminus, with the addition of a suffix-il, except for the last C-terminal amino acid, for which its full name is retained. In other words, the names

amino acids that entered into the formation of a peptide bond due to “their” COOH group end in the name of the peptide with -il: alanil, valyl, etc. (for aspartic and glutamic acid residues the names “aspartyl” and “glutamyl” are used, respectively). The names and symbols of amino acids indicate their belonging to l -row, unless otherwise indicated ( d or dl).

Sometimes in the abbreviated notation the symbols H (as part of an amino group) and OH (as part of a carboxyl group) indicate the unsubstitution of the functional groups of terminal amino acids. This method is convenient for depicting functional derivatives of peptides; for example, the amide of the above peptide at the C-terminal amino acid is written H-Asn-Gly-Phe-NH2.

Peptides are found in all organisms. Unlike proteins, they have a more heterogeneous amino acid composition, in particular, they quite often include amino acids d -row. Structurally, they are also more diverse: they contain cyclic fragments, branched chains, etc.

One of the most common representatives of tripeptides is glutathione- found in the body of all animals, plants and bacteria.

Cysteine ​​in the composition of glutathione makes it possible for glutathione to exist in both reduced and oxidized forms.

Glutathione is involved in a number of redox processes. It functions as a protein protector, i.e., a substance that protects proteins with free SH thiol groups from oxidation with the formation of disulfide bonds -S-S-. This applies to those proteins for which such a process is undesirable. In these cases, glutathione takes on the action of an oxidizing agent and thus “protects” the protein. During the oxidation of glutathione, intermolecular cross-linking of two tripeptide fragments occurs due to a disulfide bond. The process is reversible.

12.3. Secondary structure of polypeptides and proteins

High molecular weight polypeptides and proteins, along with the primary structure, are also characterized by higher levels of organization, which are called secondary, tertiary And quaternary structures.

The secondary structure is described by the spatial orientation of the main polypeptide chain, the tertiary structure by the three-dimensional architecture of the entire protein molecule. Both secondary and tertiary structure are associated with the ordered arrangement of the macromolecular chain in space. The tertiary and quaternary structure of proteins is discussed in a biochemistry course.

It was shown by calculation that one of the most favorable conformations for a polypeptide chain is an arrangement in space in the form of a right-handed helix, called α-helix(Fig. 12.3, a).

The spatial arrangement of an α-helical polypeptide chain can be imagined by imagining that it wraps around a certain

Rice. 12.3.α-helical conformation of the polypeptide chain

cylinder (see Fig. 12.3, b). On average, there are 3.6 amino acid residues per turn of the helix, the pitch of the helix is ​​0.54 nm, and the diameter is 0.5 nm. The planes of two neighboring peptide groups are located at an angle of 108°, and the side radicals of amino acids are located on the outside of the helix, i.e., they are directed as if from the surface of the cylinder.

The main role in securing such a chain conformation is played by hydrogen bonds, which in the α-helix are formed between the carbonyl oxygen atom of each first and the hydrogen atom of the NH group of each fifth amino acid residue.

Hydrogen bonds are directed almost parallel to the axis of the α-helix. They keep the chain twisted.

Typically, protein chains are not completely helical, but only partially. Proteins such as myoglobin and hemoglobin contain fairly long α-helical regions, such as the myoglobin chain

75% spiralized. In many other proteins, the proportion of helical regions in the chain may be small.

Another type of secondary structure of polypeptides and proteins is β-structure, also called folded sheet, or folded layer. Elongated polypeptide chains are arranged in folded sheets, linked by many hydrogen bonds between the peptide groups of these chains (Fig. 12.4). Many proteins contain both α-helical and β-sheet structures.

Rice. 12.4.Secondary structure of the polypeptide chain in the form of a folded sheet (β-structure)

Amino acids are heterofunctional compounds that necessarily contain two functional groups: an amino group - NH 2 and a carboxyl group - COOH, associated with a hydrocarbon radical. The general formula of the simplest amino acids can be written as follows:

Because amino acids contain two different functional groups that influence each other, the characteristic reactions differ from those of carboxylic acids and amines.

Properties of amino acids

The amino group - NH 2 determines the basic properties of amino acids, since it is capable of attaching a hydrogen cation to itself via a donor-acceptor mechanism due to the presence of a free electron pair at the nitrogen atom.

The -COOH group (carboxyl group) determines the acidic properties of these compounds. Therefore, amino acids are amphoteric organic compounds. They react with alkalis as acids:

With strong acids - like bases - amines:

In addition, the amino group in an amino acid interacts with its carboxyl group, forming an internal salt:

The ionization of amino acid molecules depends on the acidic or alkaline nature of the environment:

Since amino acids in aqueous solutions behave like typical amphoteric compounds, in living organisms they play the role of buffer substances that maintain a certain concentration of hydrogen ions.

Amino acids are colorless crystalline substances that melt and decompose at temperatures above 200 °C. They are soluble in water and insoluble in ether. Depending on the R- radical, they can be sweet, bitter or tasteless.

Amino acids are divided into natural (found in living organisms) and synthetic. Among natural amino acids (about 150), proteinogenic amino acids (about 20) are distinguished, which are part of proteins. They are L-shapes. About half of these amino acids are irreplaceable, because they are not synthesized in the human body. Essential acids are valine, leucine, isoleucine, phenylalanine, lysine, threonine, cysteine, methionine, histidine, tryptophan. These substances enter the human body with food. If their quantity in food is insufficient, the normal development and functioning of the human body is disrupted. In certain diseases, the body is unable to synthesize some other amino acids. Thus, in phenylketonuria, tyrosine is not synthesized. The most important property of amino acids is the ability to enter into molecular condensation with the release of water and the formation of the amide group -NH-CO-, for example:

The high-molecular compounds obtained as a result of this reaction contain a large number of amide fragments and are therefore called polyamides.

These, in addition to the synthetic nylon fiber mentioned above, include, for example, enant, formed during the polycondensation of aminoenanthic acid. Amino acids with amino and carboxyl groups at the ends of the molecules are suitable for producing synthetic fibers.

Alpha amino acid polyamides are called peptides. Depending on the number of amino acid residues, they are distinguished dipeptides, tripeptides, polypeptides. In such compounds, the -NH-CO- groups are called peptide groups.