Amino acids and protein biosynthesis. General formula of amino acids Amino acid alkali
Organic substances, the molecule of which contains carboxyl and amine groups, are called amino acids or aminocarboxylic acids. These are vital compounds that are the basis for the construction of living organisms.
Structure
Amino acid is a monomer consisting of nitrogen, hydrogen, carbon and oxygen. Non-hydrocarbon radicals, such as sulfur or phosphorus, can also be attached to an amino acid.
The conditional general formula of amino acids is NH 2 -R-COOH, where R is a divalent radical. In this case, there can be several amino groups in one molecule.
Rice. 1. Structural structure of amino acids.
From a chemical point of view, amino acids are derivatives of carboxylic acids, in the molecule of which hydrogen atoms are replaced by amino groups.
Kinds
Amino acids are classified in several ways. Classification according to three criteria is presented in the table.
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View |
Description |
Example |
According to the arrangement of amine and carboxyl groups relative to each other |
α-amino acids |
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β-, γ-, δ-, ε- and other amino acids |
β-aminopropionic acid (two atoms between groups), ε-aminocaproic acid (five atoms) |
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By variable part (radical) |
Aliphatic (fatty) |
Lysine, serine, threonine, arginine |
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aromatic |
Phenylalanine, tryptophan, tyrosine |
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Heterocyclic |
Tryptophan, histidine, proline |
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Imino acids |
Proline, hydroxyproline |
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By physical and chemical properties |
Non-polar (hydrophobic) |
Do not interact with water |
Glycine, valine, leucine, proline |
Polar (hydrophilic) |
interact with water. Divided into uncharged, positively and negatively charged |
Lysine, serine, aspartate, glutamate, glutamine |
Rice. 2. Scheme for the classification of amino acids.
The names are formed from the structural or trivial names of carboxylic acids with the prefix "amino-". The numbers show where the amino group is located. Trivial names ending in "-in" are also used. For example, 2-aminobutanoic or α-aminobutyric acid.
Properties
Amino acids differ in physical properties from other organic acids. All compounds of the class are crystalline substances, readily soluble in water, but poorly soluble in organic solvents. They melt at high temperatures, have a sweetish taste and readily form salts.
Amino acids are amphoteric compounds. Due to the presence of a carboxyl group -COOH exhibit the properties of acids. The amino group -NH 2 determines the basic properties.
Chemical properties of compounds:
- combustion:
4NH 2 CH 2 COOH + 13O 2 → 8CO 2 + 10H 2 O + 2N 2;
- hydrolysis:
NH 2 CH 2 COOH + H 2 O ↔ NH 3 CH 2 COOH + OH;
- reaction with alkali solution:
NH 2 CH 2 COOH + NaOH → NH 2 CH 2 COO-Na + H 2 O;
- reaction with acid solution:
2NH 2 CH 2 COOH + H 2 SO 4 → (NH 3 CH 2 COOH) 2 SO 4;
- esterification:
NH 2 CH 2 COOH + C 2 H 5 OH → NH 2 CH 2 COOC 2 H 5 + H 2 O.
Amino acid monomers form long polymers - proteins. One protein can include several different amino acids. For example, the casein protein contained in milk consists of tyrosine, lysine, valine, proline, and a number of other amino acids. Proteins perform different functions in the body depending on their structure.
Rice. 3. Proteins.
What have we learned?
From the 10th grade chemistry lesson, we learned what amino acids are, what substances they contain, how they are classified. Amino acids include two functional groups - an amino group -NH 2 and a carboxyl group -COOH. The presence of two groups determines the amphoteric nature of amino acids: the compounds have the properties of bases and acids. Amino acids are divided according to several criteria and differ in the number of amino groups, the presence or absence of a benzene ring, the presence of a heteroatom, and interaction with water.
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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:
Since 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 able to attach a hydrogen cation to itself according to the 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 like 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 medium:
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 with decomposition 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-shaped. Approximately half of these amino acids are indispensable, 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 amount in food is insufficient, the normal development and functioning of the human body is disrupted. In certain diseases, the body is not able to synthesize some other amino acids. So, with 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 an amide group -NH-CO-, for example:
The macromolecular compounds obtained as a result of such a reaction contain a large number of amide fragments and, therefore, are called polyamides.
In addition to the above-mentioned synthetic nylon fiber, these include, for example, enanth, which is formed during the polycondensation of aminoenanthic acid. Synthetic fibers are suitable for amino acids with amino and carboxyl groups at the ends of the molecules.
Polyamides of alpha-amino acids are called peptides. Based on the number of amino acid residues dipeptides, tripeptides, polypeptides. In such compounds, the -NH-CO- groups are called peptide groups.
Isomerism and amino acid nomenclature
The isomerism of amino acids is determined by the different structure of the carbon chain and the position of the amino group, for example:
The names of amino acids are also widespread, in which the position of the amino group is indicated by the letters of the Greek alphabet: α, β, y, etc. So, 2-aminobutanoic acid can also be called α-amino acid:
Methods for obtaining amino acids
Amino acids are the structural chemical units or "building blocks" that make up proteins. Amino acids are 16% nitrogen, which is their main chemical difference from the other two most important nutrients - carbohydrates and fats. The importance of amino acids for the body is determined by the huge role that proteins play in all life processes.
Every 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 part of the fluids and bones. Enzymes and hormones that catalyze and regulate all processes in the body are also proteins. A deficiency of these nutrients in the body can lead to water imbalance, which causes swelling.
Each protein in the body is unique and exists for specific purposes. 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 foods. Thus, it is the amino acids, and not the proteins themselves, that are the most valuable elements of nutrition. In addition to the fact that amino acids form proteins that make up the tissues and organs of the human body, some of them act as neurotransmitters (neurotransmitters) or are their precursors.
Neurotransmitters are chemicals that transmit nerve impulses from one nerve cell to another. Thus, some amino acids are essential for the normal functioning of the brain. Amino acids contribute to the fact that vitamins and minerals adequately perform their functions. Some amino acids provide energy directly 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 get them with 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 missing, the formation of proteins stops. This can lead to a wide variety of serious problems - from indigestion to depression and stunted growth.
How does such a situation arise? Easier than you might imagine. Many factors lead to this, even if your diet is balanced and you consume enough protein. Malabsorption in the gastrointestinal tract, infection, trauma, stress, certain medications, the aging process, and other nutrient imbalances in the body can all lead to essential amino acid deficiencies.
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 fact, it does not contribute to the preservation of health.
Excess protein creates additional stress for the kidneys and liver, which need to process the products of protein metabolism, the main one being ammonia. It is very toxic to the body, so the liver immediately processes it into urea, which then enters the bloodstream to the kidneys, 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 that is important, but the quality of proteins consumed with food. Currently, it is possible to obtain essential and non-essential amino acids in the form of biologically active food supplements.
This is especially important in various diseases and when using reduction diets. Vegetarians need such supplements containing essential amino acids so that the body receives everything necessary for normal protein synthesis.
There are different types of amino acid supplements. Amino acids are part of some multivitamins, protein mixtures. There are commercially available formulas containing complexes of amino acids or containing one or two amino acids. They are presented in various forms: capsules, tablets, liquids and powders.
Most amino acids exist in two forms, the chemical structure of one being a mirror image of the other. They are called D- and L-forms, such as D-cystine and L-cystine.
D means dextra (right in Latin), and L means levo (respectively, left). These terms denote the direction of rotation of the helix, which is the chemical structure of a given molecule. Proteins of animal and plant organisms are created mainly by L-forms of amino acids (with the exception of phenylalanine, which is represented by D, L forms).
Food supplements containing L-amino acids are considered to be more suitable for the biochemical processes of the human body.
Free, or unbound, amino acids are the purest form. Therefore, when choosing an amino acid supplement, preference should be given to products containing L-crystalline amino acids as 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, best in the morning or between meals with a small amount of vitamins B6 and C. If you are taking an amino acid complex that includes all essential amino acids, this is best done 30 minutes after or 30 minutes before a meal. It is best to take both individual essential amino acids and a complex of amino acids, but at different times. Separate amino acids should not be taken for a long time, especially in high doses. Recommend reception within 2 months with a 2-month break.
Alanine
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 form of alanine, beta-alanine, is a constituent of pantothenic acid and coenzyme A, one of the most important catalysts in the body.
Arginine
Arginine slows down the growth of tumors, including cancer, by stimulating the body's immune system. It increases the activity and size of the thymus, 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). Seminal fluid contains arginine, so it is sometimes used in the treatment of infertility in men. There is also a large amount of arginine in the connective tissue and skin, so its use is effective for various injuries. Arginine is an important metabolic component in muscle tissue. It helps to maintain an optimal nitrogen balance in the body, as it is involved in the transportation and neutralization of excess nitrogen in the body.
Arginine helps to reduce weight, as it causes some reduction in body fat stores.
Arginine is part of many enzymes and hormones. It has a stimulating effect on the production of insulin by the pancreas as a component of vasopressin (pituitary hormone) and helps the synthesis of growth hormone. Although arginine is synthesized in the body, its production may be reduced in newborns. Sources of arginine are chocolate, coconuts, dairy products, gelatin, meat, oats, peanuts, soybeans, walnuts, white flour, wheat, and wheat germ.
People with viral infections, including Herpes simplex, should not take arginine supplements and should avoid arginine-rich foods. 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 occurring in the central nervous system: it prevents both excessive excitation and excessive inhibition. It is involved in the synthesis of amino acids in the liver.
Since this amino acid enhances vitality, supplementation 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 violations of liver function. In addition, it stimulates the immune system by increasing the production of immunoglobulins and antibodies.
Aspartic acid is found in large quantities in plant 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, in the process of oxidation of which energy is released. 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, and 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 reduce 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 variants of muscular dystrophies are believed to be associated with carnitine deficiency. With such diseases, people should receive more of this substance than is required by the norms.
It can be synthesized in the body in the presence of iron, thiamine, pyridoxine, and the amino acids lysine and methionine. Synthesis of carnitine is carried out in the presence of also 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.
Moreover, methionine and lysine (amino acids necessary for the synthesis of carnitine) are also not found in plant foods in sufficient quantities.
Vegetarians should take supplements or eat lysine-fortified foods such as corn flakes to get the carnitine they need.
Carnitine is presented in dietary supplements in various forms: in the form of D, L-carnitine, D-carnitine, L-carnitine, acetyl-L-carnitine.
It is preferable to take L-carnitine.
citrulline
Citrulline is predominantly found in the liver. It increases energy supply, stimulates the immune system, and in the process of metabolism turns into L-arginine. It neutralizes ammonia, which damages liver cells.
cysteine and cystine
These two amino acids are closely related to each other, each cystine molecule consists of two cysteine molecules connected to each other. Cysteine is very unstable and readily converts to L-cystine, and thus one amino acid is readily converted 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 part of alpha-keratin - the main protein of nails, skin and hair. It promotes collagen formation and improves skin elasticity and texture. Cysteine is a component of other body proteins, 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 with vitamin C and selenium.
Cysteine is a precursor of glutathione, a substance that has a protective effect on liver and brain cells from damage from alcohol, certain drugs, and toxic substances found in cigarette smoke. Cysteine dissolves better than cystine, and is more quickly utilized in the body, so 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, and cancer. It accelerates recovery after operations, burns, binds heavy metals and soluble iron. This amino acid also accelerates the burning of fat and the formation of muscle tissue.
L-cysteine has the ability to break down mucus in the airways, which is why it is often used for bronchitis and 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 glutathione levels 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. If you have cystinuria, a rare genetic condition that causes cystine stones, you should not take cysteine.
Dimethylglycine
Dimethylglycine is a derivative of glycine, the simplest amino acid. It is a component of many important substances, such as the amino acids methionine and choline, some hormones, neurotransmitters and DNA.
Dimethylglycine is found in small amounts in meat products, seeds, and grains. Although no symptoms are associated with dimethylglycine deficiency, dimethylglycine supplementation has a number of beneficial effects, including improved energy and mental performance.
Dimethylglycine also stimulates the immune system, reduces cholesterol and triglycerides in the blood, helps normalize blood pressure and glucose levels, and also contributes to the normalization of the function of many organs. It is also used for epileptic seizures.
Gamma aminobutyric acid
Gamma-aminobutyric acid (GABA) acts as a neurotransmitter of the central nervous system in the body and is indispensable for metabolism in the brain. It is formed from another amino acid - glutamine. It reduces the activity of neurons and prevents overexcitation of nerve cells.
Gamma-aminobutyric acid relieves arousal and has a calming effect, it can be taken in the same way as tranquilizers, but without the risk of addiction. 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 dysfunction. In addition, GABA is prescribed for attention deficit disorder. An excess of gamma-aminobutyric acid, however, can increase anxiety, cause shortness of breath, and trembling of the limbs.
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 neutralizes ammonia by removing nitrogen atoms in the process of forming another amino acid - glutamine. This process is the only way to neutralize 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 free form in muscles. It very easily penetrates the blood-brain barrier and in the brain cells passes into glutamic acid and vice versa, in addition, it increases the amount of gamma-aminobutyric acid, which is necessary to maintain the normal functioning of the brain.
This amino acid also maintains a normal acid-base balance in the body and a healthy state of the gastrointestinal tract, and 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 adding 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, glutamine supplements are used by bodybuilders and in various diets, as well as to prevent muscle loss in diseases such as malignancy and AIDS, after surgery and during prolonged bed rest.
Additionally, glutamine is also used in the treatment of arthritis, autoimmune diseases, fibrosis, diseases of the gastrointestinal tract, peptic ulcers, connective tissue diseases.
This amino acid improves brain activity and is therefore used for epilepsy, chronic fatigue syndrome, impotence, schizophrenia and senile dementia. L-glutamine reduces 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 is easily destroyed by heat. 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 will be converted to ammonia and pyroglutamic acid. Do not take glutamine for cirrhosis of the liver, kidney disease, Reye's syndrome.
Glutathione
Glutathione, like carnitine, is not an amino acid. According to the 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 necessary for carbohydrate metabolism, and also slows down aging due to the effect on lipid metabolism and prevents the occurrence of atherosclerosis. Glutathione deficiency affects primarily the nervous system, causing impaired coordination, thought processes, and tremors.
The amount of glutathione in the body decreases with age. In this regard, older people should receive it additionally. However, it is preferable to use nutritional 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 non-essential amino acids in the body.
It is part of many antacid preparations used for diseases of the stomach, it is useful for repairing damaged tissues, as 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 good prostate health. It acts as an inhibitory neurotransmitter and thus may prevent epileptic seizures.
Glycine is used in the treatment of manic-depressive psychosis, it can also be effective in hyperactivity. An excess of glycine in the body causes a feeling of fatigue, 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, is part of the myelin sheaths that protect nerve cells, and is also required for the formation of red and white blood cells. Histidine protects the body from the damaging effects of radiation, promotes the removal of heavy metals from the body and helps with AIDS.
Too high a histidine content can lead to stress and even mental disorders (arousal and psychosis).
Inadequate levels of histidine in the body worsen rheumatoid arthritis and 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 dietary supplements containing histidine, niacin and pyridoxine (necessary for the synthesis of histamine) may be effective in sexual disorders.
Since histamine stimulates the secretion of gastric juice, the use of histidine helps with digestive disorders associated with low acidity of gastric juice.
People suffering from manic depressive illness should not take histidine unless a deficiency of this amino acid has been clearly established. Histidine is found in rice, wheat and rye.
Isoleucine
Isoleucine is one of the BCAAs and essential amino acids required for the synthesis of hemoglobin. It also stabilizes and regulates blood sugar levels and energy supply processes. Isoleucine metabolism occurs in muscle tissue.
Combined with isoleucine and valine (BCAA) increases endurance and promotes muscle tissue recovery, which is especially important for athletes.
Isoleucine is essential for many mental illnesses. Deficiency of this amino acid leads to symptoms similar to hypoglycemia.
Dietary sources of isoleucine include almonds, cashews, chicken meat, chickpeas, eggs, fish, lentils, liver, meat, rye, most seeds, soy proteins.
There are biologically active food supplements containing isoleucine. In this case, it is necessary to maintain the correct balance between isoleucine and the other two branched-chain amino acids BCAA - leucine and valine.
Leucine
Leucine is an essential amino acid, together with isoleucine and valine, one of the three branched-chain amino acids BCAA. Acting together, they protect muscle tissue and are sources of energy, and also contribute to the restoration of bones, skin, muscles, so their use is often recommended during the recovery period after injuries and operations.
Leucine also somewhat lowers blood sugar levels and stimulates the release of growth hormone. Dietary sources of leucine include brown rice, beans, meat, nuts, soy and wheat flour.
Biologically active food supplements containing leucine are used in combination with valine and isoleucine. They should be taken with caution so as not to cause hypoglycemia. Excess leucine can increase the amount of ammonia in the body.
Lysine
Lysine is an essential amino acid found in almost all proteins. It is necessary for normal bone formation and growth in children, promotes calcium absorption and maintains 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 operations and sports injuries. It also lowers serum triglyceride levels.
Lysine has an antiviral effect, especially against viruses that cause herpes and acute respiratory infections. Supplementation containing lysine in combination with vitamin C and bioflavonoids is recommended for viral diseases.
Deficiency of this essential amino acid can lead to anemia, bleeding in the eyeball, enzyme disorders, irritability, fatigue and weakness, poor appetite, slow growth and weight loss, as well as reproductive system disorders.
Food sources of lysine are cheese, eggs, fish, milk, potatoes, red meat, soy and yeast products.
Methionine
Methionine is an essential amino acid that helps to process fats, preventing their deposition 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 the neutralization of toxic metals), reduces muscle weakness, protects against radiation exposure, and is useful for osteoporosis and chemical allergies.
This amino acid is used in the complex therapy of rheumatoid arthritis and toxemia of pregnancy. Methionine has a pronounced antioxidant effect, as it is a good source of sulfur, which inactivates free radicals. It is used for Gilbert's syndrome, liver dysfunction. Methionine is also required for the synthesis of nucleic acids, collagen and many other proteins. It is useful for women taking oral hormonal contraceptives. Methionine lowers the level of histamine in the body, which can be useful in schizophrenia when the amount of histamine is elevated.
Methionine in the body is converted to cysteine, which is the 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.
Food sources of methionine: legumes, eggs, garlic, lentils, meat, onions, soybeans, seeds, and yogurt.
Ornithine
Ornithine aids in the release of growth hormone, which promotes fat burning in the body. This effect is enhanced by the use of ornithine in combination with arginine and carnitine. Ornithine is also necessary for the immune system and liver function, participating in detoxification processes and 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 repair damaged tissues.
Dietary supplements containing ornithine should not be given to children, pregnant or nursing mothers, or persons with a history of schizophrenia.
Phenylalanine
Phenylalanine is an essential amino acid. In the body, it can turn 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, and suppresses appetite. It is used in the treatment of arthritis, depression, period pain, migraine, obesity, Parkinson's disease and schizophrenia.
Phenylalanine occurs in three forms: L-phenylalanine (the natural form and it is she who is part of most proteins in the human body), D-phenylalanine (a 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.
Biologically active food supplements containing phenylalanine are not given to pregnant women, people with anxiety attacks, diabetes, high blood pressure, phenylketonuria, pigmentary melanoma.
Proline
Proline improves skin condition by increasing collagen production and reducing its loss with age. Helps in the restoration of the cartilaginous surfaces of the joints, strengthens the ligaments and the heart muscle. To strengthen the connective tissue, proline is best used in combination with vitamin C.
Proline enters the body mainly from meat products.
Serene
Serine is necessary 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. As a moisturizing agent, it is included in many cosmetic products and dermatological preparations.
Taurine
Taurine is found in high concentrations 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 in 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 heart rhythm disorders. Taurine has a protective effect on the brain, especially when dehydrated. It is used in the treatment of anxiety and agitation, epilepsy, hyperactivity, seizures.
Dietary supplements with taurine 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 disrupts the body's ability to absorb taurine.
In 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 is not found 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. With genetic or metabolic disorders that interfere with the synthesis of taurine, it is necessary to take dietary supplements with this amino acid.
Threonine
Threonine is an essential amino acid that contributes to the maintenance of normal protein metabolism in the body. It is important for the synthesis of collagen and elastin, helps the liver and is involved in the metabolism of fats in combination with aspartic acid and methionine.
Threonine is found in the heart, central nervous system, skeletal muscles and prevents the deposition of fat in the liver. This amino acid stimulates the immune system, as it promotes 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 required 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 to stabilize mood.
It helps with hyperactivity syndrome 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 deficiency can exacerbate coronary artery spasms.
The richest dietary sources of tryptophan include brown rice, country cheese, meat, peanuts, and soy protein.
Tyrosine
Tyrosine is a precursor to 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 to reduce fat deposits, promotes the production of melatonin and improves the functions of the adrenal glands, thyroid gland and pituitary gland.
Tyrosine is also involved in the metabolism of phenylalanine. Thyroid hormones are formed by the addition of iodine atoms to tyrosine. Therefore, it is not surprising that low plasma tyrosine is associated with hypothyroidism.
Other symptoms of tyrosine deficiency include low blood pressure, low body temperature, and restless leg syndrome.
Tyrosine dietary supplements are used to relieve stress and are thought 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 useful in Parkinson's disease. Natural sources of tyrosine are almonds, avocados, bananas, dairy products, pumpkin seeds, and sesame seeds.
Tyrosine can be synthesized from phenylalanine in the human body. Phenylalanine supplements are best taken at bedtime or with foods high in carbohydrates.
Against the background of treatment with monoamine oxidase inhibitors (usually prescribed for depression), you should almost completely abandon products containing tyrosine and do not take dietary supplements with tyrosine, as this can lead to an unexpected and sharp rise in blood pressure.
Valine
Valine is an essential amino acid that has a stimulating effect, one of the BCAA amino acids, so it can be used by muscles as an energy source. Valine is essential for muscle metabolism, repair of damaged tissues, and for maintaining normal nitrogen metabolism in the body.
Valine is often used to correct severe amino acid deficiencies resulting from drug addiction. Its excessively high levels in the body can lead to symptoms such as paresthesia (goosebumps) up to hallucinations.
Valine is found in the following foods: cereals, meat, mushrooms, dairy products, peanuts, soy protein.
Supplementation of valine should be balanced with other BCAAs, L-leucine and L-isoleucine.
Amino acids, proteins and peptides are examples of the compounds described below. Many biologically active molecules include several chemically distinct 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:
Mostly found in nature α - acids. Proteins are composed of 19 amino acids and one imino acid ( C 5 H 9NO 2 ):
The simplest amino acid- glycine. The remaining 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, tk. contain in their composition 2 opposite functional groups - an amino group and a hydroxyl group. Therefore, they react with both acids and alkalis:
Acid-base conversion can be represented as:
In an acidic environment, α-amino acids act as bases (according to the amino group), and in an alkaline environment they act as acids (according to the carboxyl group). For some amino acids, the radical (R) can also be ionized, in connection with which all amino acids can be divided into charged and uncharged (at a physiological pH value of 6.0 - 8.0) (see Table 4). As an example of the former, aspartic acid and lysine can be given:
If the amino acid radicals are neutral, they do not affect the dissociation of the α-carboxyl or α-amino group, and the pK values (the negative logarithm indicating the pH value at which these groups are half dissociated) remain relatively constant.
The pK values for the α-carboxy (pK 1) and α-amino group (pK 2) differ greatly. At pH< pK 1 почти все молекулы аминокислоты протежированы и заряжены положительно. Напротив, при рН >pK 2 almost all amino acid molecules are negatively charged, since the α-carboxyl group is in a dissociated state.
Therefore, depending on the pH of the medium, amino acids have a total zero positive or negative charge. The pH value at which the total charge of the molecule is zero, and it does not move in the electric field either to the cathode or to the anode, is called the isoelectric point and is denoted by pI.
For neutral α-amino acids, the pI value is found as the arithmetic mean between two pK values:
When the pH of the solution is less than pI, the amino acids are protonated and, being positively charged, move in the electric field to the cathode. The reverse picture is observed at pH > pI.
For amino acids containing charged (acid or basic) radicals, the isoelectric point depends on the acidity or basicity of these radicals and their pK (pK 3). The pI value for them is found by the following formulas:
for acidic amino acids:
for basic amino acids:
In the cells and intercellular fluid of the human and animal body, the pH of the medium is close to neutral, so the basic amino acids (lysine, arginine) have a positive charge (cations), acidic amino acids (aspartic, glutamine) have a negative charge (anions), and the rest exist in the form of a bipolar zwitterion.
Stereochemistry of amino acids
An important feature of protein α-amino acids is their optical activity. With the exception of glycine, all of them are built asymmetrically, and therefore, being dissolved in water or hydrochloric acid, they are able to rotate the plane of polarization of light. Amino acids exist as spatial isomers belonging to the D- or L-series. The L- or D-configuration is determined by the type of structure of the compound relative to the asymmetric carbon atom (a carbon atom bonded to four different atoms or groups of atoms). In formulas, an asymmetric carbon atom is denoted by an asterisk. Figure 3 shows projection models of L- and D-configurations of amino acids, which are, as it were, a mirror image of each other. All 18 optically active protein amino acids belong to the L-series. However, D-amino acids have been found in the cells of many microorganisms and in the antibiotics produced by some of them.
Rice. 3. Configuration of L- and D- amino acids
The structure of proteins
Based on the results of studying the products of protein hydrolysis and put forward by A.Ya. Danilevsky ideas about the role of peptide bonds -CO-NH- in the construction of a protein molecule, the German scientist E. Fischer proposed at the beginning of the 20th century the peptide theory of the structure of proteins. According to this theory, proteins are linear polymers of α-amino acids linked by a peptide bond - polypeptides:
In each peptide, one terminal amino acid residue has a free α-amino group (N-terminus) and the other has a free α-carboxyl group (C-terminus). The structure of peptides is usually depicted starting from the N-terminal amino acid. In this case, amino acid residues are indicated by symbols. For example: Ala-Tyr-Leu-Ser-Tyr- - Cys. This entry denotes a peptide in which the N-terminal α-amino acid is lyatsya alanine, and the C-terminal - cysteine. When reading such a record, the endings of the names of all acids, except for the last ones, change to - "yl": alanyl-tyrosyl-leucyl-seryl-tyrosyl--cysteine. The length of the peptide chain in peptides and proteins found in the body ranges from two to hundreds and thousands of amino acid residues.
To determine the amino acid composition, proteins (peptides) are subjected to hydrolysis:
In a neutral environment, this reaction proceeds very slowly, but is accelerated in the presence of acids or alkalis. Protein hydrolysis is usually carried out in a sealed ampoule in a 6M hydrochloric acid solution at 105°C; under such conditions, complete disintegration occurs in about a day. In some cases, the protein is hydrolyzed under milder conditions (at a temperature of 37-40 °C) under the action of biological enzyme catalysts for several hours.
Then the amino acids of the hydrolyzate are separated by chromatography on ion-exchange resins (sulfopolystyrene cation exchanger), isolating separately the fraction of each amino acid. To wash out amino acids from the ion exchange column, buffers with increasing pH are used. Aspartate, which has an acidic side chain, is removed first; arginine with the main side chain is washed out last. The sequence of removal of amino acids from the column is determined by the washout profile of standard amino acids. Fractionated amino acids are determined by the color formed when heated with ninhydrin:
In this reaction, colorless ninhydrin is converted; to a blue-violet product whose color intensity (at 570 nm) is proportional to the amount of amino acid (only proline gives a yellow color). By measuring the intensity of staining, it is possible to calculate the concentration of each amino acid in the hydrolyzate and the number of residues of each of them in the protein under study.
Currently, such an analysis is carried out with the help of automatic devices - amino acid analyzers (see Fig. Diagram of the device below). The device gives the result of the analysis in the form of a graph of the concentrations of individual amino acids. This method has found wide application in the study of the composition of nutrients, clinical practice; with its help, in 2-3 hours, you can get a complete picture of the qualitative composition of amino acids in products and biological fluids.
Rice. Scheme of an amino acid analyzer: 1 - washing solution (buffer with variable pH); 2 - chromatographic column (protein hydrolyzate is added to the upper part of the column, then leaching begins); 3 - ninhydrin solution; 4 - water bath (heating is necessary to accelerate the reaction of ninhydrin with amino acids); 5 - spectrophotometer and recording device; 6 - chromatogram, each peak of which corresponds to one amino acid, and the peak area is proportional to the concentration of the amino acid in the hydrolyzate.