Physiological functions of amino acids
Amino acids are linked by peptide bonds to form peptides and protein. Amino acids, peptides and protein are the basic components of tissues and cells of organic life, which play an important role in life activities.
Some amino acids not only can form protein, but also participate in some special metabolic reactions, showing some important characteristics.
(1) lysine
Lysine is an essential amino acid. Because the content of lysine in cereal food is very low, and it is easy to be destroyed and lacked during processing, it is called the first restrictive amino acid.
Lysine can regulate the metabolic balance of human body. Lysine provides structural components for the synthesis of carnitine, which will promote the synthesis of fatty acids in cells. Adding a small amount of lysine to food can stimulate the secretion of pepsin and gastric acid, improve the secretion of gastric juice, stimulate appetite and promote the growth and development of children. Lysine can also improve the absorption and accumulation of calcium in the body and accelerate bone growth. If lysine is lacking, it will cause anorexia and nutritional anemia due to insufficient gastric juice, which will lead to central nervous system obstruction and dysplasia.
Lysine can also be used as an auxiliary drug of diuretics in medicine to treat lead poisoning caused by the reduction of chloride in blood, and can also form salts with acidic drugs (such as salicylic acid, etc.) to reduce adverse reactions, and it can inhibit severe hypertension when combined with methionine.
Herpes simplex virus is the cause of cold sores, febrile herpes and genital herpes, while its closely related herpes zoster virus is the cause of chickenpox, herpes zoster and infectious mononucleosis. The research published by Lilly Laboratory of Indianapolis in 1979 shows that lysine supplementation can accelerate the recovery of herpes infection and inhibit its recurrence.
Long-term administration of lysine can antagonize another amino acid-arginine, and arginine can promote the growth of herpes virus.
(2) Methionine
Methionine is an essential amino acid containing sulfur, which is closely related to the metabolism of various sulfur-containing compounds in organisms. When methionine is lacking, it will cause loss of appetite, slow growth or no weight gain, kidney enlargement and iron accumulation in the liver, and finally lead to liver necrosis or fibrosis.
Methionine can also use its methyl group to methylate toxic substances or drugs and play a detoxification role. Therefore, methionine can be used to prevent and treat liver diseases such as chronic or acute hepatitis and liver cirrhosis, and can also be used to alleviate the toxic reactions of harmful substances such as arsenic, chloroform, carbon tetrachloride, benzene, pyridine and quinoline.
(3) tryptophan
Tryptophan can be transformed into an important neurotransmitter in human brain-5- hydroxytryptamine, which can neutralize adrenaline and norepinephrine and improve the duration of sleep. When the content of 5- hydroxytryptamine in the animal brain decreases, it shows abnormal behavior, hallucinations of insanity and insomnia. In addition, 5- hydroxytryptamine has a strong vasoconstrictive effect and can be found in many tissues, including platelets and intestinal mucosal cells. After injury, the body will release 5- hydroxytryptamine to stop bleeding. Tryptophan is often used as an anti-stuffy agent, an antispasmodic agent, a gastric secretion regulator, a gastric mucosal protective agent and a strong anti-coma agent in medicine.
(4) Valine, leucine, isoleucine and threonine
Valine, leucine and isoleucine are all branched-chain amino acids and essential amino acids. When valine is insufficient, the central nervous system function of rats will be disordered, and the limbs will tremble due to ataxia. By dissecting brain tissue, it was found that there was degeneration of erythrocytes. Patients with advanced liver cirrhosis were prone to hyperinsulinemia due to liver function damage, which led to the decrease of branched-chain amino acids in blood, and the ratio of branched-chain amino acids to aromatic amino acids decreased from 3.0~3.5 in normal people to 1.0~ 1.5. Therefore, injections of branched-chain amino acids such as valine were often used to treat liver failure and other diseases. In addition, it can also be used as a therapeutic agent to accelerate wound healing.
Leucine can be used to diagnose and treat sudden hyperglycemia in children, and can also be used as a dizziness therapeutic agent and a nutritional tonic. Isoleucine can treat neurological disorders, anorexia and anemia, and it is also very important in muscle protein metabolism.
Threonine is one of the essential amino acids, which is involved in fat metabolism. Liver steatosis occurs when threonine is lacking.
(5) aspartic acid and asparagine
Aspartic acid is an important component of tricarboxylic acid cycle because it promotes tricarboxylic acid cycle by deamination to oxaloacetic acid. Aspartic acid is also closely related to ornithine cycle, which is responsible for transforming ammonia in blood into urea and excreting it. At the same time, aspartic acid is also the raw material for synthesizing nucleic acid precursors such as orotic acid.
Aspartic acid is usually made into salts of calcium, magnesium, potassium or iron for use. Because these metals, after combining with aspartic acid, can pass through the cell membrane and enter the cell through active transport. The mixture of potassium aspartate and magnesium aspartate is mainly used to eliminate fatigue and treat diseases such as heart disease, liver disease and diabetes in clinic. Potassium aspartate can be used to treat hypokalemia, and iron salt can treat anemia.
The proliferation of different cancer cells needs to consume a lot of certain amino acids. It is considered to be an effective way to treat cancer to look for the analogues of this amino acid-metabolic antagonists. Asparaginase can prevent the proliferation of cancer cells (leukemia) that need asparagine. The analogue of asparagine, S- carbamoyl-cysteine, has obvious anti-leukemia effect in animal experiments. At present, there are many kinds of amino acid anticancer drugs 10, such as N- acetyl -L- phenylalanine, N- acetyl -L- valine, etc., and some of them can inhibit cancer cells as high as 95%.
(6) Cystine and cysteine
Cystine and cysteine are non-essential amino acids containing sulfur, which can reduce the demand for methionine in human body. Cystine is an indispensable substance for skin formation, which can accelerate the recovery of burn wounds and chemical protection of radiation injury, and stimulate the increase of red blood cells and white blood cells.
The sulfhydryl group (-SH) carried by cysteine has many physiological functions, which can alleviate the poisoning degree of toxic substances or drugs (phenol, benzene, naphthalene, cyanide ions) and also have preventive and therapeutic effects on radiation. N- acetyl -L- cysteine, a derivative of cysteine, has the effect of reducing viscosity due to the action of sulfhydryl group, and can be used as a mucolytic agent to prevent and treat the difficulty of expectoration such as bronchitis. In addition, cysteine can promote hair growth and can be used to treat alopecia. Other derivatives, such as L- cysteine methyl ester hydrochloride, can be used to treat bronchitis and exudative inflammation of nasal mucosa.
(7) glycine
Glycine is the simplest amino acid, which can be produced by serine losing a carbon. Glycine is involved in the synthesis of purines, porphyrins, creatine and glyoxylic acid, and glyoxylic acid is oxidized to produce oxalic acid, which promotes the occurrence of hereditary disease oxaluria. In addition, glycine can be combined with a wide variety of substances to be excreted from bile or urine. In addition, glycine can provide a nitrogen source for non-essential amino acids and improve the tolerance of amino acid injection in vivo. The use of glycine together with glutamic acid and alanine is quite effective in preventing and treating complications of prostatic hypertrophy, dysuria, frequent urination, residual urine and other symptoms.
(8) Histidine
Histidine is a nonessential amino acid for adults, but an essential amino acid for children. Adding a small amount of histidine to the diet of patients with chronic uremia will increase the speed of amino acid binding into hemoglobin and reduce nephrogenic anemia, so histidine is also an essential amino acid for patients with uremia.
The imidazole group of histidine can form a coordination compound with Fe2+ or other metal ions to promote the absorption of iron, so it can be used to prevent and treat anemia. Histidine can reduce the acidity of gastric juice, relieve the pain of gastrointestinal surgery, relieve vomiting and burning sensation in the stomach during pregnancy, inhibit the digestive tract ulcer caused by autonomic nervous tension, and also have effects on allergic diseases, such as asthma. In addition, histidine can dilate blood vessels and lower blood pressure, so it is clinically used for the treatment of angina pectoris, cardiac insufficiency and other diseases. The content of histidine in the blood of patients with rheumatoid arthritis decreased significantly, and the grip strength, walking and erythrocyte sedimentation rate were improved after using histidine.
Under the action of histidine decarboxylase, histidine is decarboxylated to form histamine. Histamine has a strong vasodilation effect, and is related to a variety of allergic reactions and inflammation. In addition, histamine can stimulate pepsin and gastric acid.
(9) Glutamic acid
Glutamate and aspartic acid are excitatory transmitters. They are the most abundant amino acids in the central nervous system of mammals, and their excitatory effects are limited to the central nervous system. When the content of glutamic acid reaches 9%, as long as10–15 mol of glutamic acid is increased, it can produce excitatory effects on cortical neurons. Therefore, glutamic acid is essential to improve and maintain brain function.
Glutamate is decarboxylated by glutamate decarboxylase to form γ -aminobutyric acid, which is a substance in brain tissue that can inhibit the excitement of central nervous system. When the content of γ -aminobutyric acid decreases, it will affect cell metabolism and cell function.
Various derivatives of glutamic acid, such as dimethylaminoethanol acetylglutamic acid, are clinically used to treat dyskinesia, memory disorder and encephalitis caused by cerebrovascular disorder. γ -aminobutyric acid is effective for memory disorder, speech disorder, paralysis and hypertension, while γ -aminobutyric acid is effective for local paralysis, memory disorder, speech disorder, instinctive renal hypertension, epilepsy and mental retardation.
Glutamate, like aspartic acid, is also closely related to the tricarboxylic acid cycle and can be used to treat liver coma and other diseases. Glutamine, an amide derivative of glutamic acid, has obvious effect on gastric ulcer, because the amino group of glutamine is transferred to glucose, and glucosamine, a component of mucin in digestive mucosa, is generated.
(10) Serine, Alanine and Proline
Serine is a precursor for the synthesis of purine, thymidine and choline. Alanine plays an important role in the process of protein synthesis in vivo. During metabolism in vivo, it produces keto acid through deamination and sugar according to glucose metabolism. The pyrrole ring in proline molecule is closely related to hemoglobin in structure. Hydroxyproline is one of the components of collagen. The imbalance of proline and hydroxyproline concentration in the body will weaken the toughness of cartilage and ligament tissue in teeth and bones. Proline derivatives combined with diuretics have antihypertensive effects.
Taurine acid
Taurine is a component of bezoar.
Taurine is commonly found in milk, brain and heart of animals, with the highest content in muscle. Taurine exists in free form and does not participate in protein metabolism. Only algae exists in plants, but it has not been found in higher plants. Taurine is metabolized by cysteine in the body.
Lack of taurine will affect growth, vision, normal growth of heart and brain.
Patients infected by bacteria consume taurine in the body due to the proliferation of bacteria, which will also lead to taurine deficiency and changes in fundus electroretinogram. However, taurine supplementation will improve fundus lesions. Because humans can only synthesize taurine in a limited way, taurine in the diet is very important.
The content of taurine in dairy products is very low. In poultry, the taurine content of black poultry meat is higher than that of white meat. Compared with poultry and livestock, the taurine content in seafood is the highest, for example, the taurine content in oysters, clams and mussels can reach more than 400mg/ 100g, and heating and cooking have no effect on the taurine content. All kinds of daily foods, including grains, fruits and vegetables, do not contain taurine.
Arginine acid
(1) Arginine is a component of ornithine cycle and has extremely important physiological functions. Eating more arginine can increase the activity of arginase in the liver and help to convert ammonia in the blood into urea and excrete it. Therefore, arginine is effective in treating hyperammonemia, liver dysfunction and other diseases.
Arginine is a kind of double-base amino acid, although it is not an essential amino acid for adults, in some cases, such as immature body development or under severe stress conditions, if arginine is lacking, the body cannot maintain positive nitrogen balance and normal physiological function. If the patient lacks arginine, it will lead to high blood ammonia and even coma. Arginine is also necessary for infants who are congenitally deficient in some enzymes of urea cycle, otherwise they cannot maintain their normal growth and development.
The important metabolic function of arginine is to promote wound healing, which can promote the synthesis of collagen tissue, so it can repair wounds. The increase of arginase activity can be observed in wound secretion, which also indicates that the demand for arginine near the wound is greatly increased. Arginine can promote the microcirculation around the wound and promote the early healing of the wound.
The immune regulation function of arginine can prevent the degeneration of thymus (especially after injury), and arginine supplementation can increase the weight of thymus and promote the growth of lymphocytes in thymus.
Arginine supplementation can also reduce the volume of animals with tumors, reduce the metastasis rate of tumors and improve the survival time and survival rate of animals.
In the immune system, besides lymphocytes, the activity of phagocytes is also related to arginine. After adding arginine, its enzyme system can be activated, making it more capable of killing target cells such as tumor cells or bacteria.
Dr. Zheng Jianxian, Professor of South China University of Technology
Amino acids and human health
Amino acids are the most basic substances that constitute the protein of organisms and are related to life activities. They are the basic units that constitute protein molecules in organisms and are closely related to life activities of organisms. It has a special physiological function in antibodies and is one of the indispensable nutrients in organisms.
First, the basic substance that constitutes the human body is the material basis of life.
1.constitutes one of the most basic substances of the human body.
Protein, lipids, carbohydrates, inorganic salts, vitamins, water and dietary fiber are the most basic substances that make up the human body.
As the basic unit of protein molecule, amino acid is undoubtedly one of the most basic substances in human body.
There are more than 20 kinds of amino acids that make up the human body, which are: tryptophan, methionine, threonine, valine, lysine, histidine, leucine, isoleucine, alanine, phenylalanine, cystine, cysteine, arginine, glycine, serine, tyrosine, 3.5. Diiodotyrosine, glutamic acid, aspartic acid, proline, hydroxyproline, arginine, citrulline, Ukraine. These amino acids exist in nature and can be synthesized in plants, but the human body can't synthesize them all. Eight of them are not synthesized by human body and must be provided by food, which are called "essential amino acids". These eight essential amino acids are tryptophan, threonine, methionine, valine, lysine, leucine, isoleucine and phenylalanine. Others are "nonessential amino acids". Histidine can be synthesized in human body, but its synthesis speed can not meet the needs of the body, and some people also list it as "essential amino acid". Cystine, tyrosine, arginine, serine and glycine are listed as "semi-essential amino acids" because they can be synthesized in vivo, but their synthetic raw materials are essential amino acids, and cystine can replace 80% ~ 90% of methionine, and tyrosine can replace 70% ~ 75% of phenylalanine to play the role of essential amino acids. For example, according to its metabolic pathway in vivo, it can be divided into "ketogenic amino acids" and "glycogenic amino acids"; According to its chemical properties, it can be divided into neutral amino acids, acidic amino acids and basic amino acids, most of which are neutral.
2. Material basis of life metabolism
The emergence, existence and extinction of life are all related to protein, as Engels said: "protein is the material basis of life, and life is a form of protein's existence." If there is a lack of protein in human body, the body constitution will be reduced, the development will be delayed, the resistance will be weakened, anemia will be weak, and edema will be formed in severe cases, even life-threatening. Once protein is lost, life will cease to exist, so some people call protein "the carrier of life". It can be said that it is the first element of life.
The basic unit of protein is amino acid. If the human body lacks any essential amino acids, it will lead to abnormal physiological functions, affect the normal metabolism of antibodies, and finally lead to diseases. Similarly, if some non-essential amino acids are lacking in human body, antibody metabolism disorder will occur. Arginine and citrulline are very important for the formation of urea; Insufficient intake of cystine will cause insulin decrease and blood sugar increase. Another example is that the demand for cystine and arginine is greatly increased after trauma. If it is lacking, protein cannot be successfully synthesized even if the heat energy is sufficient. In a word, amino acids can play the following roles through metabolism in human body: ① Synthesis of tissue protein; (2) into acids, hormones, antibodies, creatine and other ammonia-containing substances; (3) into carbohydrates and fats; ④ Oxidation into carbon dioxide, water and urea to generate energy. Therefore, the existence of amino acids in human body not only provides an important raw material for the synthesis of protein, but also provides a material basis for promoting growth, normal metabolism and maintaining life. If the human body lacks or reduces one of them, the normal life metabolism of the human body will be hindered, and even various diseases will occur or life activities will be terminated. This shows how much amino acids are needed in human life activities.
Second, the position and role in food nutrition
In order to survive, human beings must ingest food to maintain the normal physiological, biochemical and immune functions of antibodies, as well as life activities such as growth, development and metabolism. The comprehensive process that food is digested, absorbed and metabolized in the body to promote the growth and development of antibodies, improve intelligence and fitness, resist aging and prevent diseases and prolong life is called nutrition. The effective ingredients in food are called nutrients.
Protein, lipids, carbohydrates, inorganic salts (i.e., minerals, containing macroelements and microelements), vitamins, water and dietary fiber, which constitute the most basic substances of the human body, are also nutrients needed by the human body. They have their own unique nutritional functions in the body, but they are closely related in the process of metabolism, and participate in, promote and regulate life activities. The body connects with the outside world through food, keeps the internal environment relatively constant, and completes the unity and balance of the internal and external environment.
What role do amino acids play in these nutrients?
1.protein is digested and absorbed in the body through amino acids.
Protein, as the first nutritional element in the body, plays an obvious role in food nutrition, but it can't be directly used in the human body, but is used by becoming small molecules of amino acids. That is, it is not directly absorbed by the human body in the gastrointestinal tract, but is decomposed into low-molecular-weight peptides or amino acids by various digestive enzymes in the gastrointestinal tract, and then absorbed in the small intestine and enters the liver along the hepatic portal vein. Some amino acids are decomposed or synthesized into protein in the liver; The other part of amino acids continue to be distributed to various tissues and organs with blood, and can be selected freely to synthesize various specific tissue protein. Under normal circumstances, the speed at which amino acids enter the blood is almost equal to its output, so the content of amino acids in normal people's blood is quite constant. If calculated by amino nitrogen, the content is 4 ~ 6 mg per 100 ml of plasma and 6.5 ~ 9.6 mg per 100 ml of blood cells. After a full meal in protein, a large number of amino acids were absorbed, and the level of amino acids in blood temporarily increased, and after 6-7 hours, the content returned to normal. It shows that amino acid metabolism in the body is in dynamic balance, with blood amino acids as its balance hub, and liver is an important regulator of blood amino acids. Therefore, food protein is digested and decomposed into amino acids and then absorbed by human body, and antibodies use these amino acids to synthesize their own protein. The human body's need for protein is actually the need for amino acids.
2. Play the role of nitrogen balance
When the quality and quantity of protein in daily diet are appropriate, the nitrogen intake is equal to the nitrogen discharged from feces, urine and skin, which is called the total balance of nitrogen. In fact, it is the balance between the continuous synthesis and decomposition between protein and amino acids. The daily intake of protein of normal people should be kept within a certain range. When the intake suddenly increases or decreases, the body can still adjust the metabolism of protein to maintain the nitrogen balance. Excessive intake of protein, beyond the body's regulatory capacity, will destroy the balance mechanism. If you don't eat protein at all, the tissue protein in your body will still decompose, and negative nitrogen balance will continue to appear. If you don't take timely measures to correct it, the antibody will eventually die.
3. Turn into sugar or fat
A-keto acid produced by amino acid catabolism is metabolized along the metabolic pathway of sugar or fat with different characteristics. A-keto acid can be synthesized into new amino acids, or converted into sugar or fat, or decomposed into CO2 and H2O by tricarboxylic cycle oxidation, and energy is released.
4. Participate in the formation of enzymes, hormones and some vitamins.
The chemical essence of enzymes is protein (amino acid molecular composition), such as amylase, pepsin, cholinesterase, carbonic anhydrase, transaminase, etc. The composition of nitrogen-containing hormone is protein or its derivatives, such as growth hormone, thyroid stimulating hormone, adrenaline, insulin, intestinal fluid stimulating hormone, etc. Some vitamins are transformed from amino acids or exist in combination with protein. Enzymes, hormones and vitamins play a very important role in regulating physiological functions and catalyzing metabolism.
5. Requirement of essential amino acids for human body
The requirement of essential amino acids for adults is about 20%-37% of that for protein.
Third, the application in medical treatment
Amino acids are mainly used to prepare compound amino acid infusion in medicine, and also used as therapeutic drugs and drugs for synthetic peptides. At present, there are more than 100 kinds of amino acids used as drugs, including 20 kinds of amino acids that constitute protein and more than 0/00 kinds of amino acids that constitute non-protein.
Compound preparation composed of various amino acids plays a very important role in modern intravenous nutrition infusion and "elemental diet" therapy. It plays an active role in maintaining the nutrition of critically ill patients and saving their lives, and has become one of the indispensable medical varieties in modern medicine.
Amino acids such as glutamic acid, arginine, aspartic acid, cystine, and L-dopa can be used alone to treat some diseases, which are mainly used to treat liver diseases, digestive tract diseases, encephalopathy, cardiovascular diseases, respiratory diseases, and to improve muscle vitality, pediatric nutrition and detoxification. In addition, amino acid derivatives are promising in cancer treatment.
Fourth, the relationship with aging
If the elderly lack protein, they will decompose more and their synthesis will slow down. Therefore, generally speaking, the elderly need more protein than young adults, and the demand for methionine and lysine is also higher than young adults. People over 60 years old should consume about 70g of protein every day, and it is required that protein contains all kinds of essential amino acids with proper proportion, so as to achieve high-quality protein and prolong life.