References:
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 and play an important role in life activities.
Some amino acids can not only 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 can 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, anorexia and nutritional anemia will be caused by 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). ) to reduce adverse reactions, combined with methionine can inhibit severe hypertension.
Herpes simplex virus is the cause of cold sores, fever herpes and genital herpes, while herpes zoster virus closely related to it is the cause of chickenpox, herpes zoster and infectious mononucleosis. The research published by Lilly Laboratory in 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, which 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 deficient, it will cause loss of appetite, slow growth or no weight gain, kidney enlargement, 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 chronic or acute hepatitis, liver cirrhosis and other liver diseases, 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 converted into serotonin, an important neurotransmitter in the human brain, which can neutralize adrenaline and norepinephrine and improve the duration of sleep. When the content of 5- hydroxytryptamine in animals' brains decreases, it shows the hallucinations of abnormal behavior, insanity and insomnia. In addition, serotonin has a strong vasoconstrictive effect and can be found in many tissues, including platelets and intestinal mucosal cells. After injury, the body will release serotonin to stop bleeding. Tryptophan is commonly used in medicine as anti-nasal congestion agent, antispasmodic agent, gastric secretion regulator, gastric mucosal protective agent and powerful anti-coma agent.
(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 the brain tissue, it was found that there was erythrocyte degeneration. Patients with advanced liver cirrhosis are prone to hyperinsulinemia due to liver function damage, which leads to the decrease of branched-chain amino acids in blood, and the ratio of branched-chain amino acids to aromatic amino acids decreases from 3.0~3.5 in normal people to 1.0~ 1.5. Therefore, branched-chain amino acids such as valine are 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 nutritional supplement. 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 involved in fat metabolism. Hepatic steatosis occurs when threonine is deficient.
(5) Aspartic acid and asparagine
Aspartic acid is an important part of tricarboxylic acid cycle, because it promotes tricarboxylic acid cycle by deamination to oxaloacetic acid. Aspartic acid is also closely related to the ornithine cycle, which is responsible for converting ammonia in the blood into urea and excreting it out of the body. 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 calcium salt, magnesium salt, potassium salt or iron salt. Because these metals, after binding with aspartic acid, can enter cells through cell membrane and active transport. The mixture of potassium aspartate and magnesium aspartate is mainly used to eliminate fatigue and treat heart disease, liver disease, diabetes and other diseases 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. Searching for analogues of this amino acid metabolism antagonist is considered to be an effective way to treat cancer. Asparaginase can prevent the proliferation of cancer cells (leukemia) that need asparagine. S- carbamoyl cysteine, an analogue of asparagine, has obvious anti-leukemia effect in animal experiments. At present, there are 10 kinds of amino acid anticancer substances, such as N- acetyl -L- phenylalanine, N- acetyl -L- valine and so on. Some of them can inhibit cancer cells by more than 95%.
(6) Cystine and cysteine
Cystine and cysteine are non-essential amino acids containing sulfur, which can reduce the demand for methionine. Cystine is an indispensable substance for skin formation, which can accelerate the recovery of burn wounds and chemical protection against 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 reduce the poisoning degree of toxic substances or drugs (phenol, benzene, naphthalene, cyanide ions) and also prevent radiation. N- acetyl -L- cysteine is a derivative of cysteine, which has the function of reducing viscosity due to sulfhydryl group, and can be used as a mucolytic agent to prevent and treat expectoration difficulties such as bronchitis. In addition, cysteine can also 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 participates in the synthesis of purine, porphyrin, creatine and glyoxylic acid, and glyoxylic acid is oxidized to oxalic acid, which promotes the occurrence of hereditary disease oxaluria. In addition, glycine can be combined with many substances and excreted from bile or urine. In addition, glycine can provide nitrogen source for non-essential amino acids and improve the tolerance of amino acid injection in vivo. Glycine, together with glutamic acid and alanine, is very effective in preventing and treating complications of prostatic hypertrophy, dysuria, frequent urination, residual urine and other symptoms.
(8) Histidine
Histidine is a non-essential amino acid for adults, but it is 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 combining amino acids into hemoglobin and reduce renal 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 stomach burning during pregnancy, inhibit 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 to treat angina pectoris, cardiac insufficiency and other diseases. The content of histidine in 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 vasodilatory effect, which 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 added, it will stimulate 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 acetyl glutamic acid, are used to treat dyskinesia, dysmnesia and encephalitis caused by cerebrovascular disorder in clinic. γ -aminobutyric acid is effective for memory disorder, speech disorder, paralysis and hypertension, and γ -aminobutyric acid is effective for local paralysis, memory disorder, speech disorder, instinctive renal hypertension, epilepsy and mental retardation.
Glutamate, like aspartic acid, is closely related to the tricarboxylic acid cycle and can be used to treat diseases such as hepatic coma. Glutamine is an amide derivative of glutamic acid, which has obvious effect on gastric ulcer, because the amino group of glutamine is transferred to glucose to produce glucosamine, which is a component of mucin in mucosal epithelial tissue of digester.
(10) Serine, Alanine and Proline
Serine is the precursor of purine, thymidine and choline synthesis. Alanine plays an important role in the synthesis of protein in vivo. In the process of metabolism in vivo, ketoacids are produced by deamination, and sugars are produced 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 effect.
taurine
Taurine is a component of bezoar.
Taurine is ubiquitous in the milk, brain and heart of animals, and its content is the highest in muscle. Taurine exists in free form and does not participate in protein metabolism. Only algae exist in plants, but not in higher plants. Taurine is metabolized by cysteine in the body.
Lack of taurine will affect growth, vision, normal development 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 can 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 low. In poultry, the taurine content of black poultry meat is higher than that of white meat. Compared with poultry and livestock, the content of taurine in seafood is the highest, such as oysters, clams and mussels, which can be as high as 400mg/ 100g. Heating and cooking have no effect on the content of taurine. All kinds of daily foods, including grains, fruits and vegetables, do not contain taurine.
arginine
(1) arginine is a component of ornithine cycle, which 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 quite effective in treating hyperammonemia, liver dysfunction and other diseases.
Arginine is a dibasic amino acid. Although it is not an essential amino acid for adults, in some cases, such as immature body or in a state of severe stress, if arginine is lacking, the body cannot maintain a positive nitrogen balance and normal physiological functions. If the patient lacks arginine, it will lead to an increase in blood ammonia and even coma. Arginine is also necessary for infants who are congenitally deficient in some enzymes of urea cycle, otherwise normal growth and development cannot be maintained.
The important metabolic function of arginine is to promote wound healing and promote the synthesis of collagen tissue, so it can repair wounds. The increase of arginase activity can be observed in wound secretion, which also shows that the demand for arginine near the wound is greatly increased. Arginine can promote microcirculation around the wound and promote early healing of the wound.
The immunomodulatory function of arginine can prevent thymus degeneration (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 tumor animals, 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, it can activate its enzyme system and make it more capable of killing tumor cells or bacteria and other target cells.
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 of protein molecules in organisms and are closely related to the 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 in the human body.
Protein, lipids, carbohydrates, inorganic salts, vitamins, water and dietary fiber are the most basic substances that constitute 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, namely: tryptophan, methionine, threonine, valine, lysine, histidine, leucine, isoleucine, alanine, phenylalanine, cystine, cysteine, arginine, glycine, serine, tyrosine and 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 cannot 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 list it as "essential amino acid". Cystine, tyrosine, arginine, serine and glycine are classified as "semi-essential amino acids" because they can be synthesized in vivo, but their synthetic raw materials are all essential amino acids. 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 the body, 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 existence in protein." If the human body lacks protein, its physique will be reduced, its development will be delayed, its 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". Can be said to be 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 function, affect the normal metabolism of antibodies and eventually lead to diseases. Similarly, if the human body lacks some non-essential amino acids, there will also be disorder of antibody metabolism. Arginine and citrulline are very important for the formation of urea. Insufficient intake of cystine will cause insulin decrease and blood sugar increase. For example, the demand for cystine and arginine has greatly increased after trauma. Without it, even if the heat energy is sufficient, protein can't be successfully synthesized. In a word, amino acids can play the following roles in human body through metabolism: ① synthesis of tissue protein; (2) into acid, hormone, antibody, 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 important raw materials 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 or life activities will be terminated. This shows how many amino acids are needed for human life activities.
Second, the position and role in food nutrition
In order to survive, human beings must eat 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 of food being digested, absorbed and metabolized in the body, promoting antibody growth and development, improving intelligence and physique, resisting aging, preventing diseases and prolonging life is called nutrition. The effective ingredients in food are called nutrients.
Protein, lipids, carbohydrates, inorganic salts (that is, minerals, which contain a large number of elements and trace elements), vitamins, water and dietary fiber, which constitute the most basic substances of the human body and 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, participating, promoting and regulating life activities together. The body communicates with the outside world through food, keeping the internal environment relatively constant, and completing the unity and balance of the internal and external environment.
What role do amino acids play in these nutrients?
1. The digestion and absorption of protein in the body is completed by amino acids.
Protein, as the first nutrient element in the body, plays an obvious role in food nutrition, but it can't be directly used in the human body, but can be 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; Another part of amino acids continue to distribute to various tissues and organs with blood, and can freely choose to synthesize various specific tissue proteins. Under normal circumstances, the speed of amino acids entering the blood is almost equal to its output speed, 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 the content returned to normal after 6-7 hours. It shows that amino acid metabolism in the body is in a 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. What the human body needs 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 of continuous synthesis and decomposition between protein and amino acids. Normal people's daily intake of protein should be kept within a certain range. When the intake suddenly increases or decreases, the body can still regulate the metabolism of protein and 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 proteins in your body will still decompose and negative nitrogen balance will continue to appear. If measures are not taken to correct it in time, the antibody will eventually die.
Step 3 turn into sugar or fat
α -keto acids produced by amino acid catabolism are metabolized along different sugar or fat metabolic pathways. α-keto acids can be synthesized into new amino acids, or converted into sugar or fat, or decomposed into CO2 and H2O through cyclic oxidation of tricarboxylic acid, releasing energy.
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 nitrogen-containing hormone is protein or its derivatives, such as growth hormone, thyroid stimulating hormone, adrenaline, insulin, intestinal juice stimulating hormone, etc. Some vitamins are converted 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. The demand for essential amino acids in human body
Adults' demand for essential amino acids is about 20%-37% of that of 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 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 100 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 "element 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 levodopa can be used alone to treat some diseases, mainly for treating liver diseases, digestive tract diseases, encephalopathy, cardiovascular diseases and respiratory diseases, as well as improving muscle vitality, pediatric nutrition and detoxification. In addition, amino acid derivatives are also promising in cancer treatment.
Fourth, the relationship with aging.
If the elderly lack protein, they will decompose more and synthesize more slowly. 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 the age of 60 should consume about 70g of protein every day, and it is required that protein contains all kinds of essential amino acids in proper proportion, so as to achieve high-quality protein and prolong life.
Yu Chuanlong (China Medical Science and Technology Press)
Amino acids and health of the elderly
The American space shuttle Discovery sent Glenn (77), the world's oldest astronaut, into space. For the elderly, this day is called the greatest day and the most eye-catching day. Glenn will explore space again in his later years. He wants to help medical science experiments. Protein decomposition of the elderly and the biological experiment of human amino acids are important research. Amino acids and the health of the elderly should be studied not only on earth, but also in space. Because amino acids are related to the life span and aging of the elderly, this is too important. Why is it important? You will know in the following paragraphs. 1. Physiological changes and amino acids in the elderly
It is generally believed that people are old after 60. The physiological and nutritional status of the elderly changes with the progress of the elderly. The changes of protein in the elderly can be summarized in two ways: one is to synthesize tissue protein and various active substances; The second is decomposition, which organizes protein decomposition to produce energy and waste. For growing infants and adolescents, synthesis is greater than decomposition, so the body grows gradually; For the average adult, synthesis equals decomposition, so the weight is relatively stable. For the elderly, in the process of human aging, protein metabolism is dominated by decomposition, while synthetic metabolism is gradually slow, and protein in the body is gradually consumed, often showing a negative nitrogen balance. For example, hemoglobin synthesis is reduced, so anemia is a common senile disease; Due to the function of enzymes and the decrease of small intestine function, protein is not fully decomposed during absorption, and peptides in the body increase and free amino acids decrease. Low renal function in the elderly affects the reabsorption of amino acids, and the decline of liver function also reduces the utilization rate of peptides. In recent years, it has been reported that the elderly are given the same nutritional conditions as young adults, but the plasma amino acids (Valeriana officinalis, leucine, lime, eggs, silk and alanine) of the elderly are reduced, especially the branched-chain amino acids (Valeriana officinalis, leucine and isoleucine) are insufficient. Some people think that high concentration of branched-chain amino acids can provide synthesis. When supplying branched-chain amino acids, it can provide energy by producing adenosine triphosphate (ATP), reduce protein decomposition and enhance the synthesis of protein by promoting insulin secretion. Branched-chain amino acids have been used to maintain nitrogen balance and promote protein synthesis abroad. There are amino acids for liver disease, kidney disease and children in China.
Due to the absorption or utilization of amino acids. Aging affects immune function, and changes in immune activity also affect the functions of other organs. Such as infection, cancer, immune complex disease, autoimmune disease, amyloidosis and other diseases increase in the elderly, which easily leads to aging and death.
2. Amino acids and longevity
In order to promote the health of the elderly, such as anti-aging, improving the body's resistance and promoting the function of immune mechanism, food needs to be rich in trace elements or sugars. However, the material basis of immunity is protein, and there is no immune substance in human body that is not made of protein. Such as immunoglobulin, antibody, antigen, complement, etc. Even the content of protein in white blood cells, lymphocytes and phagocytes is above 90%. Therefore, if the human body is not short of protein or amino acids, the above trace elements and polysaccharides will play a role. If it is missing, no amount of use is useless. With the development of nutrition and biochemistry, new research shows that although the human body can synthesize some non-essential amino acids, it is easy to lack them in severe stress (including mental stress, anxiety and ideological burden) or some diseases. If it is lacking, it will have a bad influence on the human body. These amino acids are called conditionally essential amino acid. Such as taurine, arginine and glutamine.
Under normal circumstances, the lack of essential amino acids will reduce the immune response of body fluids. For example, in tryptophan-deficient rats, IgG and IgM receptors are inhibited, but normal antibody production can be maintained when tryptophan is supplemented again; The lack of phenylalanine and tyrosine can inhibit the reaction of rat immune cells to tumor cells; The deficiency of methionine and cystine can also lead to the obstacle of antibody synthesis. It has been proved that the balance of amino acids also has this adverse effect. Therefore, essential amino acids play an important role in immunity. To prolong the life span of the elderly, we must improve immunity and pay attention to the supply of essential amino acids. At present, the essential amino acids closely related to life span are:
Taurine: The source of taurine in human body is self-synthesis and intake from diet. The biosynthesis of taurine is that methionine is converted into cystine by vulcanization and then synthesized by cystine. After a series of enzymatic reactions, many higher animals, including humans, have lost the ability to synthesize enough taurine to maintain the overall level of taurine in their bodies, so they need to take taurine from their diet to meet their needs. It is reported that taurine plays a role in the aging of the central nervous system; The degeneration of nervous system in old age is one of the most complicated and profound processes in all systems of the whole body. The aging of central nervous system has obvious changes in morphology or biochemistry, and the mechanism of synthesis, release, reabsorption and transport of monoamine and amino acid neurotransmitters has increased year by year. Lipofuscin is a characteristic substance in the aging process, and the increase of lipofuscin in the brain is one of the signs of nerve aging. When a large amount of lipofuscin accumulates in the cytoplasm of neurons, the nucleus and cytoplasm are compressed and deformed, which affects the normal metabolic function of neurons. The content of lipofuscin in tissues increases obviously during aging, but taurine can decrease it, increase the activity of superoxide dismutase (SOD), and inhibit the modification of low density lipoprotein (LDL) by malondialdehyde (MDA), a product of lipid peroxidation. At the same time, the reaction product of taurine and glucose shows strong antioxidant effect, which can prevent egg yolk lecithin from being oxidized into lipid peroxide, so it has obvious anti-aging effect.
Arginine: Although arginine is not an essential amino acid, it cannot maintain nitrogen balance and normal physiological function under severe stress (such as disease or injury) or arginine deficiency, so it is a conditionally essential amino acid. According to the latest theory, arginine is an essential substance in the enzymatic metabolic pathway of nitric oxide (NO) reacting with citrulline. The main biochemical function of NO or relaxation factor derived from endothelial cells is to stimulate the body to increase the level of cyclic guanylate in phagocytes and stimulate the production of interleukin to regulate the phagocytic function of macrophages. Arginine-related NO enzyme system has also been found in vascular endothelial cells, Cooper's cells in brain tissue and liver, which can lead to hormone secretion in these organs and tissues, thus playing an immune role. Amino acid injection can also be used to improve the immunity of the elderly.
Glutamine: Under normal circumstances, it is a non-essential amino acid. However, under stress conditions such as strenuous exercise, injury and infection. The demand for glutamine greatly exceeds the ability of the body to synthesize glutamine, which reduces the content of glutamine in the body, and this decrease will reduce the synthesis of protein, atrophy of intestinal mucosa and low immune function, so it is also called conditionally essential amino acid.
Recently, it is found that the intestine is the largest immune organ and the third barrier of the human body. The first two barriers are blood-brain barrier and placental barrier. If there is no nutrition supply in the intestine, the intestine will be malnourished, which will weaken the immune function of the intestine and lead to bacterial translocation. Animal experiments have proved that if animals are supplemented with total intravenous infusion or essential diet without glutamine, the villi of small intestine will shrink, the intestinal wall will become thinner and the intestinal immune function will be reduced. Intravenous infusion of 2% glutamylase (about 25% of total amino acids) has a significant effect on restoring intestinal villi atrophy and immune function. Glutamine plays an important role in maintaining the function of intestinal mucosa and improving the immunity, especially for the elderly.
3. How do the elderly scientifically supplement amino acids?
With the increase of age, the amount of amino acids required by the elderly decreases. The protein quality of a healthy elderly protein is 60% ~ 70% of that of young adults. This may be related to the decrease of skeletal muscle, but it can't be concluded that protein needs to decrease in the elderly. The elderly are mainly catabolic, with decreased secretion of gastric juice and pepsin, decreased acidity of gastric juice and decreased digestion and absorption of protein. In addition, the intake of heat energy is low, and the retention of dietary nitrogen is reduced, so the elderly need less protein than adults. Generally speaking, in a normal diet, the intake of protein is 0.7 ~ 1.0g/kg body weight to maintain the nitrogen balance, and 1.0 ~ 1.2g/kg body weight to achieve the balance. Accordingly, the daily supply of protein is about 60 ~ 75g, of which 1/3 is animal protein. If the heating ratio in protein is considered, 12% ~ 14% is more suitable. The study of amino acid metabolism shows that the requirements of threonine, tryptophan and methionine are different from those of young people, and a suitable essential amino acid model is needed.