What are amino acids good for?

Amino Acids

Amino acids are simple organic compounds that occur naturally in the body and contain nitrogen and hydrogen. They are being considered the building blocks of proteins.

There are twenty amino acids (AA) which have been found to occur in all proteins and for which genetic codon exits. Each of these has one or more genetic codon which is present within the molecule of specific messenger RNA which themselves is produced under the direction of a gene occurring in DNA molecules. DNA is a sequence of four nucleotides namely, adenine, guanine, cytosine, and thymine. Their exact sequence determines genetic codon. Each set of three nucleotides in the DNA codes for one amino acid attached to one another. These are arranged in 64 different combinations, more than enough to code 20 amino acids. Out of 64 codons, there are three codon UAA, UAG, and UGA which do not code for any amino acid and hence are known as a stop codon. Every gene starts with initiation codon AUG which encode the AA methionine. In this way, amino acids are playing an essential role within DNA molecule and also helpful in its synthesis by manufacturing purines and pyrimidines e.g. alanine, serine, aspartic acid etc.

List of Amino Acids

Glutamine | Glutamic Acid | Cysteine | Aspartic Acid | Asparagine | Arginine | Alanine | Valine | Tyrosine | Tryptophan | Threonine | Serine | Selenocysteine | Pyrrolysine | Proline | Phenylalanine | Methionine | Lysine | Leucine | Isoleucine | Histidine | Glycine


Glutamine is the amino acid with uncharged polar side chains. The polarity is due to the presence of functional groups in their structure that forms the hydrogen bond with the water. The functional groups in the glutamine are the amide groups. Glutamine amino acid is a non-essential as it is synthesized in our body from the other amino acid, mainly the glutamic acid. CAA and CAG are two of its codons. Glutamine has been found in an abundant amount in our blood.

amino acids glutamine


Although it need not be given via food as it is manufactured in our body itself but it is richly present in many foods. Some of its sources include:

  • Animal sources: It is found in large amount in the meat, fish, eggs, chicken, dairy products like milk, cheese etc.
  • Plant sources: In plants, it is found in many vegetables like in spinach, cabbage, and raw parsley. It is also present in beans, wheat etc


This amino acid glutamine, which contains an amide linkage with the ammonia at the gamma-carboxyl, is formed from the glutamine amino acid catalyzed by an enzyme called glutamine synthetase. This reaction is driven by the hydrolysis of ATP. In addition to producing glutamine amino acid for the protein synthesis, this reaction also serves as a major mechanism for the detoxification of the ammonia, especially in the brain and liver.


  • Glutamine can also give rise to another amino acid from which it has arisen itself i.e. glutamic acid. It reacts with water and gives rise to glutamic acid along with generation of ammonia. This ammonia is then used for neutralization of the hydrogen ions in renal tubules. This is its important function as this amino acid regulates the acid-base balance in the kidney.
  • Glutamic acid crosses the blood-brain barrier and is found useful for the brain. It is said to be the brain fuel.
  • It is important for our muscles as well as it synthesizes muscles proteins and prevents the muscles from wasting. It is found useful in treating wasting of muscles due to some diseases.
  • Glutamine is glucogenic and gives rise to glucose which serves as a source of energy in our body.
  • It also donates carbon atom which is important for the citric acid cycle.
  • It is important for the intestinal linings where it is located and provides nutrients there. This lead to a normal function of the intestinal villi.
  • Glutamine has been found to use up by the white blood cells of our body; therefore it also performs an important function for our immune system.
  • It also plays role in gats metabolism in the body.
  • It also produces glutathione in the liver. Glutathione is essential for detoxification of harmful free radicals.
  • It has also been found to regulate our blood glucose levels. Normal blood glucose level is important for our brain since our brain utilizes glucose.

These are some of its function. These days it is also available in the supplement forms. These are helpful for treating a number of chronic diseases. They also improve the functions of our brain.

Glutamic Acid

Glutamic acid is an amino acid with acidic side chain and a negative charge at neutral pH. It is nonessential amino acid as it is synthesized in the body. It gives rise to intermediates of the citric acid cycle so it is glucogenic. It has codons GAG and GAA. Its salt sand carboxylate anion is called glutamates.

amino acids glutamic


Glutamic acid is richly present in our normal diet. Some of its sources are.

  • Animal source: poultry, meat, fish, egg, Kombu and dairy products.
  • Plant sources: Glutamic acid is present in the wheat with the ratio of thirty-five percent of the protein.


It is synthesized in the cytosol of hepatocytes by another amino acid the glutarate by the transfer of an amino group to the alpha-keto acid. Glutamic acid is manufactured by the reverse of oxidative deamination which is catalyzed by an enzyme glutamate dehyrdogenase.


This amino acid gives rise to many compounds essential for our body. These are

  • Glutathione: It is a tripeptide which not only contains glutamic aid but also has one molecule each of cysteine and glycine. The glutathione performs multiple functions in our body. It acts as antioxidant and detoxifies many harmful substances in our body. It plays role in immune system. It also takes part in the synthesis and repair of DNA and synthesis of protein, prostaglandin etc
  • Glutamine: The glutamine amino acid provides ammonia in the distal convoluted tubules of the kidney.
  • Alpha-ketoglutaric Acid: It shows the alpha ketoacid of glutamic acid and it enters the citric acid cycle.
  • Gamma-Aminobutyric acid (GABA): Glutamic acid gives rise to the most important neurotransmitter GABA by the reaction which is catalyzed by glutamate decarboxylase. This neurotransmitter provides postsynaptic inhibition in the central nervous system.
  • Ammonium Ion: Glutamic acid enters the mitochondria and here it gives up its amino form and forms ammonium ion which is then used for the urea synthesis.
  • Glutamic acid itself also acts as an excitatory neurotransmitter in the brain where it results in the increased firing of the neuron.
  • Glutamic acid has also used in treating a variety of diseases such as epilepsy, ulcer, mental retardation, hypoglycemic coma, and muscular dystrophies etc.
  • It has also been found beneficial in the metabolism of carbohydrates and fats. It is also helpful in the transport of potassium into the spinal fluid and across the blood-brain barrier, but it does not itself pass the blood-brain barrier.
  • Our brain also uses glutamic acid as a fuel since it is found in high levels in the blood.
  • It is also seen that treatment with glutamic acid has improved personality disorders and is also beneficial in treating that behavior which is originated from childhood.

These days glutamate has been used as food additives and flavor enhancer. It is also included in certain drugs and is available in the market as dietary supplements. It is also used to enhance plant growth and also has been found useful in the controlling of dipolar interactions.


Cysteine is an uncharged amino acid with polar side chain and hydrophobic in nature. It is sulfur-containing amino acid and S atom in cysteine is its functional group. It is also glucogenic that it only produces glucose. It is one of the non- essential amino acids which are synthesized in the body. UGU and UGC is its codon.

amino acids cysteine


Cysteine is present in the high protein food which includes:

  • Foods of animal origin These are chicken, meat, turkey, eggs, meat, yogurt, cottage cheese, and whey proteins etc
  • Foods of plant origin: These include onion, garlic, red pepper, sprouts, wheat, granola, and lentil etc.

It is needed for all ages especially in peoples with certain metabolic diseases or due to malabsorption syndromes.


Cysteine is synthesized from methionine which is also an amino acid. S-adenosyl homocysteine produced from methionine is converted into adenosine and homocysteine on hydrolysis. Homocysteine condenses with serine and forms cystathionine in the presence of enzyme cystathionine beta-synthase. Cysthatione then reacts with water and give rise to cysteine along with alpha-keto butyric acid and ammonia.


  • Cysteine is needed for the skin and it performs detoxification action in the body as it is present in keratin which is the main protein found in the nails, hairs, and skin.
  • It is essential for collagen synthesis as well as provides texture and elasticity to the skin.
  • It also forms another amino acid the taurine.
  • It acts as a precursor to glutathione which is an antioxidant. It, therefore, detoxifies the body from the free radical produced in the body which damages the cell membrane and DNA. The presence of these free radicals also results in a number of diseases like heart diseases or even cancers. So there needs to be eliminated which is done by cysteine.
  • It also has a role in the metabolism of a certain chemical found in the body, for example, heparin, biotin, coenzyme A, glutathione and lipoic acids etc.
  • It also helps in making the protective lining of the stomach and intestine strong which further is beneficial as it then prevents damage by certain drugs like aspirin etc
  • These days cysteine supplements are available in the market in the form of N-acetylcysteine NAC. Benefits of its use are that it detoxifies harmful substance in the body and performs liver protecting actions. It also has used in cough drugs where it functions to break the disulfide bone and thins the thick mucus and make it easy for a person to cough up. It has been an essential antidote for paracetamol poisoning. The recommended dose of these supplements is about 200mg.

Diseases Due to Error in Metabolism

  • A large number of inborn errors of metabolism have been found in cysteine S containing amino acid. These are homocystinuria, cystathioninuria, and cystinosis (Cystinosis is a cysteine storage disease) and cystinuria.
  • Homocystinuria is due to deficiency of enzyme cystathionine beta-synthase and patient with this disease exhibits displacement of the lens, abnormalities in the skeleton, premature arterial diseases, osteoporosis and mental retardation.
  • In cystinuria large amount of cysteine is excreted in the urine along with lysine, arginine, and ornithine.

Aspartic Acid

Aspartic acid is an amino acid with an acidic side chain. Aspartic acid is negatively charged at neutral ph. This is non-essential amino acid and is produced in the human body. Aspartic acid is glucogenic as well as ketogenic. It has two stereoisomer forms: D-aspartic acid and L-aspartic acid.

The L-aspartic acid is 20 proteinogenic amino acid which means it is a building block of protein.

amino acids aspartic


Being formed in the body it is not so needed but still, it is also found in number of foods, as follow:

  • Animal source: Aspartic acid is present in different types of meat like luncheon or sausage meat.
  • Plant sources: Aspartic acid is found in sugar cane, avocado, oat flakes, molasses, sprouting seeds etc

Supplements of aspartic acid are also selling in the market in the form of magnesium aspartate and in the sweeteners.


Aspartic acid is produced from the oxaloacetic acid by the process of transamination. Ornithine and citrulline a part of urea cycle also produced aspartic acid.


  • Aspartic acid takes part in the formation of purines and pyrimidines which are essential for DNA synthesis.
  • With the help of citrulline, it forms argininosuccinic acid which is utilized in the urea cycle.
  • It also forms oxaloacetic acid by the process of transamination. The oxaloacetic acid then enters the citric acid cycle for oxidation or gives rise to glucose by the process of gluconeogenesis.
  • Aspartic acid can be converted into amide form i.e. asparagines which releases it ammonia in cells of distal convoluted tubules of the kidney.
  • One of the most important roles of aspartic acid is that it acts as a neurotransmitter of the excitatory type in the central nervous system. It also helps in central nervous system development.
  • It has also found to play an important role in the neuroendocrine system for example in anterior pituitary it stimulates the following hormonal secretions of prolactin, growth hormone and luteinizing hormone.
  • This amino acid also has an important part in the dentin development, which is a tissue that is an essential component of teeth.
  • It also produces various other amino acids like arginine, threonine, lysine, methionine, isoleucine and lots of other nucleotides.
  • It also aids in the detoxification of liver from various drugs and chemicals.
  • As it provides energy to the body to provide resistance to fatigue also.

Diseases Due to Deficiency

The deficiency of aspartic acid results in poor cellular energy. So there will be fatigue of chronic type and stamina will be reduced then. This amino acid also results in the removal of ammonia. When its deficiency occurs, there is an increase in the amount of ammonia which will lead to brain damage and liver damage.


Asparagine amino acid is a non-essential amino acid as it is being produced in our body from the other amino acid. It is one of the natural amino acids. It has codons AAU and AAC. Its side chain functional group is carboxamide. It was first obtained from asparagus in 1932. Aspargine contains an amide linkage with ammonia at the beta-carboxyl end. It is one of the glucogenic amino acids. It is uncharged amino acid along with polar side chain.

amino acids asparagine


Although being not essential still asparagine is found in many different foods. It sources are as follow:

  • Animal sources: Some of its animal sources are meat, beef, chicken, poultry, eggs etc
  • Plant sources: Asparagine plant sources are potatoes so eating French fries will give you asparagine along with starch. It is also found on roasted coffee. Other sources are asparagus, nuts, legumes, seed, whole grains and soy etc.

Asparagine is present in plants proteins in large amount.


This amino acid in our body is formed from aspartate by asparagines synthetase by using glutamine as the amide donor. This reaction requires ATP and like the synthesis of glutamine has equilibrium far in the direction of asparagines synthesis.


  • Asparagine gives rise to aspartic acid by the reversal reaction and also gives rise to ammonia. This reaction is catalyzed by asparaginase. Aspartic acid can then be converted into oxaloacetic acid which enters the citric acid cycle then. Ammonia formed then gives rise to urea.
  • Our central nervous system also requires this amino acid where it helps in maintenance of balance or equilibrium. It is also essential for the proper functioning and health of our nerves and other cells of the body. It controls their metabolism in the brain.
  • There is a linked between asparagine with the aspartic acid. If there is a deficiency of asparagines, it will lead to low levels of aspartic acid as it’s is involved with aspartate synthesis. Due to less synthesis of aspartic acid urea cannot be synthesized and excreted. This may lead to accumulation of nitrogen-containing harmful metabolites in the blood which directly affect our brain and lead to confusion, headache, irritability or depression etc. So this amino acid should be present in normal level within our body.

Though asparagine supplements are available in the market there are no such suggestive indications to use them. People who take proper diet never feel the needs of these supplements. So one should eat healthy foods full of nutrients in order to maintain one’s life healthy and wealthy.


Arginine is an amino acid with basic side chain and positive charge. It is one of the non-essential amino acids, therefore, it is produced in our body with the help of other amino acids. In premature infants, it is essential amino acid as they cannot synthesize it. It is glucogenic amino acid and it gives rise to intermediates of the citric acid cycle by gluconeogenesis process. Its L-form is the common naturally occurring amino acid.

amino acids arginine


It is present in wide variety of foods as follow:

  • Animal source: turkey, chicken, meat, milk, cottage, yogurt, cheese, pork, beef and in a variety of seafood.
  • Plant source: Granola, wheat, peanuts, pumpkin seeds, sesame seed, cashews, almond, walnut, flour, popcorn, brown rice, etc.

It is found in chocolate as well. In our body, it is present abundantly in histones and protamines.


It is manufactured from citrulline and the reaction is catalyzed by two cytosolic enzymes namely, arginosuccinate synthetase and arginosuccinate lyase.


  • Arginine takes part in the urea cycle and results in formations of urea and ornithine on hydrolysis. Ornithine not only plays role in urea cycle but also has a role in the formation of polyamine.
  • Arginine also contributes to the formation of creatine which is very important for the muscles as it increases muscle mass and their strength.
  • Arginine also gives rise to nitric oxide along with citrulline in the presence of enzyme nitric oxide synthase. This nitric oxide plays a very important physiological role. It causes relaxation of the smooth muscles of blood vessels and therefore causes vasodilation. Nitric oxide also inhibits platelet aggregation.
  • It is essential in the good health of skin, liver, muscle, and liver.
  • It also causes stimulation of our immune system and increases the amount of T lymphocytes which are necessary to combat different types of injuries infection and traumas.
  • It has an important function in cell division and healing of a wound.
  • It removes ammonia from the body by allowing the liver to detoxify it and releases hormones. For example, it stimulates the release of insulin from the pancreas.
  • Arginine is also used in the toothpaste and provided relief from teeth hypersensitivity.
  • In the form of supplements, it has been used to improve sexual functions especially erectile dysfunctions and also to regulate blood pressure.
  • It is also helpful in lowering of cholesterol from the body.
  • Arginine also plays a role in the metabolism of muscles and it also maintains the nitrogen balance and helps in weight control as it decreases the fats content from the body.
  • Arginine is produced abundantly in case of any trauma, injury or surgery.
  • Its salts called malate salt has found use in the treatment of alcoholic hepatitis as well as an advanced stage of cirrhosis of the liver.
  • It also causes stimulation of growth hormones.
  • Arginine supplements have also been found beneficial for female fertility and reproductive system.

In a nutshell, arginine is an important amino acid in our body. One important thing is that arginine supplements though have various positive effects but they should be avoided in case patient is suffering from schizophrenia or kidney diseases.  They are also not recommended for long-term use as they can cause thickening and coarsening of the skin in the long run.


Alanine is the amino acid with non-polar aliphatic side chains being its methyl group non-reactive and is hydrophobic i.e. water repellent. It is the non-essential amino acid. It is synthesized in the body. It was first obtained in 1879. It is glucogenic amino acid means it can give rise to glucose through alanine cycle. It has simple molecular structure. It has two stereoisomers, namely DL-alanine and D-alanine.

amino acids alanine


Being non-essential it needs not to be obtained from the food. But it is present in the variety of foods.

  • Animal sources: Its animal sources are meat, eggs, fish, gelatin, milk and dairy products etc.
  • Plant sources: The plant sources include rice, nuts, legumes, corn, seed, whole grains, soy, bran etc. Alanine is also found to occur in the bacterial cell wall as well as in peptide antibiotics.


As we know alanine is manufactured in our body so it is made by different types of amino acids themselves. These include pyruvate, leucine, valine, isoleucine, alpha-ketoglutarate and oxaloacetic acid. The reaction involved is transamination. In transamination reaction, transfer of one amino acid to another amino acid occurs which results in the formation of new amino acid. The glutamic acid reacts with pyruvic acid under the presence of glutamine pyruvate transaminases (GPT) which are now called alanine aminotransferases (ALT) and gives rise to alanine and alpha-ketoglutarate. Alanine is produced in the muscle by this reaction. It is then carried to the liver by the blood where it gives rise to glutamic acid and pyruvic acid in reversible reaction. It is also formed along with lactate. When the condensation of acetaldehyde occurs with the ammonium chloride racemic alanine is produced.


  • Alanine gives rise to glutamate and pyruvate which have some important roles in our body.
  • Pyruvic acid forms glucose. The glucose so formed can go back to the muscles and thus completing the cycle what has been called the alanine-glucose cycle. Glucose is essential for energy.
  • Glutamic acid provides ammonia which is then utilized in the synthesis of urea in the liver.
  • Alanine is also needed for the metabolism of glucose and tryptophan and the vitamin B6 (pyridoxine).
  • Nowadays its supplements are available in the market with the name of beta-alanine. These have many advantages as they increase the muscular strength and power. If someone is lean, their uses increase his muscles mass. Boost the anaerobic endurance in a person and make the person strong and improves in him the ability to exercise well without getting fatigue early.
  • The alanine aminotransferase enzyme also has much importance. It is used as a test to measure the damage taking place in the liver as this enzyme is present in the liver. It is used to check cirrhosis, any viral liver disease like hepatitis, in jaundice etc.
  • There are theories that there is a linked between the high alanine level and high blood pressure. In the rats, it has also shown to reduce the cholesterol.
  • When deamination of alanine occurs, it results in the production of alkyl free radical which has lead to its use in the radiotherapy.
  • So we have seen alanine is not only needed by our body but has other benefits as well.


Valine is an essential amino acid with an aliphatic side chain. It is non-polar in nature. It has GUC, GUU, GUA, and GUG codons. It was isolated from the casein in 1901 by German chemist Emil Fischer. It is hydrophobic amino acid found in the proteins. Its shape and volume roughly resemble the threonine amino acid and the only difference is the replacement of hydroxyl group with a methyl group in the valine. It also has branched chain.

amino acids valine


Valine must be provided from the food. Some of its sources are as follow.

  • Animal origin: Valine sources from animal origin include meat, poultry, fish, dairy foods like cheese etc
  • Plant origin: Valine plant sources include lentils, peanuts, soy, mushrooms and sesame seeds.


It is normally obtained from the hydrolysis of proteins. Valine is also manufactured in the plants from the pyruvate. Several enzymes take part in this process. These include acetohydroxy acid isomeroreductase, acetolactate synthase, valine aminotransferase and dihyroxyacid dehydratase.

The racemic valine is manufactured by bromination of isovaleric acid and then amination of bromo derivatives.


  • This branched-chain amino acid undergoes transamination reaction and results in the formation of alpha-keto acid and this reaction is catalyzed by branched chain transaminase. The alpha-keto acid then gives rise to acyl CoA derivatives with the help of enzymes. Acyl-CoA derivatives then form succinyl CoA which enters into the citric acid cycle.
  • Valine has some stimulating effects. It plays role in the muscle metabolism and also helps in growth and repair of tissues. Valine also maintains nitrogen balance in our body. Valine is the glucogenic amino acid so it provides glucose.
  • A disease known as maple serum urine disease results in case of error in metabolism of valine and it is then excreted in the urine.

If someone has taken a large amount of valine, then its toxicity occurs and is characterized by crawling sensations on the skin and feelings of hallucinations. So it should be taken with care in patients suffering from any liver or kidney diseases.


Tyrosine is the amino acid with an aromatic side chain. It has hydroxyl group for H bonds and shows polarity. It is a non-essential amino acid which means it is synthesized in the body. It is glucogenic and ketogenic both.

amino acids tyrosine


In the foods, it is mainly found in those foods containing high protein content.

  • Animal sources include chicken, turkey, dairy products like yogurt, milk, cheese, and in fish.
  • The plant sources are almonds, peanuts, the seed of pumpkin, lime beans and sesame seeds etc.

Body tyrosine is mainly of dietary origin.


In our body tyrosine is produced from phenylalanine which is itself an amino acid. The reaction occurs in the presence of phenylalanine hydroxylase enzyme which is a mixed function oxidase that needs a tetrahydrobiopterine as a cofactor. This provides two hydrogens for the reaction and is then oxidized to dihydrobiopterine. The reaction also utilizes oxygen. Water is produced and the remaining ½ oxygen results in hydroxylation of phenylalanine at its para position forming a p-hydroxyphenylalanine which is also called tyrosine. The reaction also needs NADH+H+.


  • Tyrosine is known for giving lots of important products to our body. It gives rise to catecholamine e.g. adrenaline and noradrenalin and dopamine. They then function as neurotransmitters in our brain. These are important in maintaining the good balance of moods in person. If a deficiency occurs then this result in depression in a person. Dopamine further has another important physiological role in our body i.e. it stimulates the myocardial activity in the heart means it performs an isotropic action. Since it is a neurotransmitter in the brain, in case of its deficiency in the basal ganglia, an extrapyramidal disease called Parkinsonism occurs. It also acts as a prolactin release inhibiting factor in the anterior pituitary gland.
  • Tyrosine also helps in the production of tri-iodothyronine and tetraiodothyronine which are important thyroid gland hormones.
  • Tyrosine also takes part in melanin production. Melanin is the chief pigment of the skin and is also present in the eye, hairs and even brain in the substantia nigra.
  • Tyrosine also plays a role in enzyme receptors. Insulin receptor has been seemed to be a protein kinase which is tyrosine-specific. The hydroxyl group of tyrosine receives a phosphoryl group from ATP when insulin molecules become bound with the portion of receptor outside the cell.


The catabolism results in catabolic products of tyrosine which include homogentisic acid which is further broken down to fumaric acid and acetoacetic acid.


 The defects in tyrosine metabolism lead to albinism which is a group of diseases as result of a deficiency in melanin. These result in either partial or full absence of pigments from the skin, eye, and hair. There may be vision defects and photophobia. This disease occurs due to deficiency of tyrosinase enzyme.

Alkaptonuria is another disease due to deficiency of homogentisic acid oxidase that results in accumulation of homogentisic acid. A patient may have homogenetic aciduria, arthritis of large joints, and black pigmentation of cartilage and collagenous tissues.

Tyrosine interacts with monoamine oxidase inhibitors so a patient should avoid foods containing tyrosine.

Thus, tyrosine has many beneficial effects. It supplementation is also available for the persons deficient of this amino acid. It is a useful amino acid during periods of cold, stress of any kind either emotional or physical and fatigues.


Tryptophan amino acid is the essential amino acid. This means it must be provided through food to the body. It is one of the amino acids which in its molecule contains an indole ring. Tryptophan is glucogenic as well as ketogenic amino acid. It has codon UGG. It has two stereoisomers, namely L-tryptophan and D-tryptophan.

L-tryptophan can only be utilized in the structure or enzymes proteins while D – tryptophan is normally present in naturally occurring peptides. Tryptophan has aromatic side chain and is relatively polar. The N of the imidazole ring present in tryptophan gives polarity to this amino acid. It is genetically coded also.

amino acids tryptophan


Tryptophan is found in foods of animal origin as well foods of plant origin in an abundant amount. Some of the foods in which it is present are as follow:

  • Animal Origin: Chicken, turkey, fish, egg, milk, cheese, beef etc.
  • Plant origin: Nuts, peanuts, peanut butter, pumpkin seed, soy, sunflower seed, tofu, rice, banana, potato and wheat flour etc.


It has also been produced by plants and microorganism with the help of anthranilate and shikimic acid. It is then condensed by phosphoribosyl pyrophosphate which generates pyrophosphate as a by-product. When the ring opening of ribose moiety occurs which then follows reductive decarboxylase, there is a formation of indole-3-glycerine-phosphate results which transforms into indole. Thus, in the last formation of tryptophan results from the indole and serine amino acid and the reaction is catalyzed by an enzyme tryptophan synthase.


  • In our body 60mg of tryptophan gives rise to 1 mg of niacin which is a member of vitamin B complex and is essential for the metabolism of carbohydrates, proteins, and fats as well as in normal functioning of the skin, intestine, and nervous system.
  • The body should contain iron, vitamin B 12 and riboflavin in order to convert tryptophan into niacin.
  • One of the most important functions of tryptophan in our body is that it gives rise to serotonin and its derivatives.
  • It first is hydroxylated and given rise to 5-hydroxytryptophan. This compound then undergoes decarboxylation reaction to form serotonin.
  • 5-Hyroxyindole acetic acid is the major derivative which is excreted in the urine in conjugated form.
  • Serotonin is a powerful vasoconstrictor as well as it stimulates the smooth muscles contraction.
  • Serotonin also exerts a potent action on the metabolism of the brain and it also acts as a neurotransmitter in many areas of the brain. It is then involved in various functions as mood, sleep, thermoregulation, depression, appetite, and anxiety. An excess of serotonin in the brain leads to stimulation of cerebral activity whereas its deficiency produces depressant effects.
  • Tryptophan in our gastrointestinal tract is acted upon by the bacteria which produces a large number of substances for example indole, indolepyruvix acid, indoleacetic acid. These are excreted in the urine or feces.


Tryptophan catabolism gives rise to following products after complicated pathways.

  • Fromylkynurenine
  • Kynurenine
  • 3-hydroxykynurenine.

Nowadays tryptophan is available in a variety of supplement forms. It has been found good in sleep arousal along with the treatment for a number of disorders such as seasonal affective disorder, and premenstrual disorder etc.


Threonine is the uncharged polar amino acid. It is an essential amino acid as it is not manufactured in our body. It must be provided through food to our body. It has two chiral centers. It has four stereoisomers. Threonine is the hydrophilic molecules and has a hydroxyl group. It is glucogenic as well as ketogenic.

amino acids threonine


It is present protein-rich foods. Some of its sources are as follow:

  • Animal Sources: Threonine is present in high amount in meat, eggs, dairy products, cottage cheese, and fish.
  • Plant sources: Threonine is also present in many leafy vegetables, lentils, wheat, beans, mushrooms, grains, sesame seeds and nuts.

In the body, it is found in large amount in the skeletal muscles, heart, and central nervous system.


Threonine is not synthesized in our body but it is formed in many plants and microorganism with the help of various enzymes from the other amino acid asparate. These are aspartokinase, homoserine dehydrogenase, thronine synthases, homoserine kinase, and asparatate semialdehyde dehydrogenase.


  • Threonine gives rise to pyruvic acid which can form either the glucose or acetyl CoA. The latter may either enter the citric acid cycle or may form the acetoacetyl CoA which is a precursor of ketone bodies.
  • Thronine also forms glycine which itself is an important amino acid as it acts as an inhibitory neurotransmitter.
  • Threonine also gives rise to propionly-CoA which can then form succinyl CoA, an important component of the citric acid cycle.
  • It has also an important role in maintaining the normal functioning of our various systems like the central nervous system, cardiovascular system, liver and immune system.
  • It helps in the synthesis of collagen and elastin present in the skin. It maintains the normal protein balance in the body. It makes our muscle strong and powerful. It also plays role in making our teeth strong and also promotes early healing of wounds.
  • Threonine has also found to aid antibodies production which are major components of our immune system. These antibodies combat various infections, microbes, and foreign bodies.
  • Threonine also prevents fat accumulation in the liver as it enhances fats and fatty acid digestion thus helping lipotropic function of the liver.
  • Threonine supplements have seemed to be useful in treating various diseases due to a lesion on the central nervous system like amyotrophic lateral sclerosis disease as threonine produces glycine. Multiple cases of sclerosis symptoms have also been alleviated by the use of this amino acid. The dose of threonine may not be taken in excess amount as it may damage the liver and kidney functions.


Serine is the amino acid with an uncharged polar side chain. It was isolated first from the silk protein named sericin in 1865. It is a non-essential amino acid since it is synthesized in our body. It has six codon which is AGU, AGC, UCC, UCU, UGC, and UCA. It is they hydrophilic amino acid because of hydrogen bonding capacity. It has L- isomer form which is the only form of serine that takes part in the protein synthesis.

amino acids serine


Some of its sources are as follow.

  • Animal origin sources: These include meat, beef, dairy products like cheese etc.
  • Plant origin sources: These include peanuts, wheat, gluten, and soy products.
  • Biosynthesis

    In our body serine is formed from glycine amino acid. Glycine is converted into serine by the addition of hydroxymethyl group and this reaction is catalyzed by serine hydroxymethyl transferase enzymes which also requires the two coenzymes namely, tetrahydrofolate, and pyridoxal phosphate.


    • Serine is used in the synthesis of cysteine, cephalins, and choline.
    • It is utilized in the synthesis of purines and pyrimidines which further produce DNA and RNA.
    • Serine can also give rise to pyruvate and glycine.
    • Glycine is formed by the reversal of serine hydroxymethyl transferase reactions.
    • Pyruvate is produced when serine reacts with water in the presence of serine dehydratase enzyme.
    • Serine has also been found the precursor of sphingolipids and folate. These two acts as a donor of one carbon atom in biosynthesis.
    • It takes part in the muscle formation as well as in the maintenance of a normal immune system.
    • Serine is also utilized in the synthesis of tryptophan amino acid which then gives rise to important neurotransmitter the serotonin in the central nervous system. Their deficiency leads to depression, irritability, insomnia, anxiety, and confusion.
    • Serine has also been found in the component of brain proteins and nerve coverings. In the case of its deficiency, myelin sheath becomes less efficient in performing their normal functions. So serine has been found very important for our brain.
    • In skin moisturizing creams, serine is also one of the constituents.
    • It performs an important function in the catalytic role of numerous enzymes, for example, it has been found to occur in the active sites of trypsin, chymotrypsin, and various other enzymes.
    • Because of the presence of hydroxyl group in it, serine acts as a carrier of phosphoric acid in phosphoproteins.
    • Serine has found to increase the absorption of creatine. Creatine is important for muscles as it makes them strong and increases their mass.
    • It has been found that serine plays a role in the production of antibodies.
    • An enzyme called serine protease has been found to acts as a clotting factor as well as beneficial in blood coagulation disorders.

    Serine supplements have been found useful for our body. For better results, they can be taken with folic acid, niacin and vitamin B6 because these vitamins enhance its formation.


    Selenocysteine amino acid is the analog of cysteine having the same structure as that of cysteine. But here sulfur atom is replaced by selenium. It is the 21st amino acid found in the ribosome-mediated protein synthesis. It is present in the number of enzymes like tetraidothyronine deiodinase, glutathione perxidase, thioredoxine reductase, glycine reductase, formate dehydrogenase and in hydrogenases. Proteins having more than one selenocysteine residues are called selenoprotein. There is no single free pool of selenocysteine amino acid that exists within cells to be used. So it means it is an essential amino acid which is needed to be provided through food.

    amino acids selenocysteine


    Selenocysteine is found in proteins and in a variety of foods of either animal origin or plant origin.

    • Animal origin: Selenocysteine animal sources are meat, poultry, chicken, egg, cheese fish, seafood, and turkey.
    • Plant origin: Selenocysteine of plant origin contains wheat, oats, corn, rice, nuts especially of Brazil nuts, soybeans.

    Selenocysteine is available in the food in the form of selenomethionine. In some foodstuff, it occurs in the form of selenate.


    The biosynthesis of this amino acid occurs on the tRNA which needs to be first acylated with serine and then is subsequently transformed into selenocysteine by an enzyme synthase that further utilizes selenophosphate in the form of selenium donor and the cofactor pyridoxal phosphate.


    • The important functions of selenocysteine in proteins are its antioxidant activity. This is due to its lower pKa and higher reduction potential.
    • It is also used in the preparation of a variety of vitamins and lots of other supplements.
    • It is also fortified with livestock feeds.
    • Our body utilizes selenocysteine to form selenium, which is believed to play important role in preventing mercury toxicity as well as enhance liver functions.
    • People deficient with selenium have lean body mass, prone to premature aging or to heart diseases.

    Selenocysteine is not coded for in the genetic code directly. It is encoded by the UAG codon in a very special way. UAG is a stop codon.


    Pyrrolysine is the largest amino acid known which is naturally occurring. It is encoded genetically by a nucleotide sequence that usually halts the translation of mRNA.

    amino acids pyrrolysine


    It is found in a bacterium and in few species of Archaea. It is just like the lysine but it is different in having pyrrole ring which is attached to the one end of the lysine amino acid.


    In our body, pyrrolysine is produced by special transfer RNA and an enzyme called aminoacyl transfer RNA. This amino acid also forms a part of the genetic code.


    In our body, it is incorporated into active sites of many enzymes for example methyltransferase. Here on this enzyme is rotated freely. It is incorporated during the process of translation into messenger RNA with the help of codon UAG. This amino acid has not been studied too much. There are not many known functions of it.


    It contains three chiral centers which result in eight enantiomers, but only one of these is utilized. Pyrrolysine is a labile amino acid and it can easily be destroyed by heat and acid hydrolysis. This amino acid was also found to be involved in the methanogenesis. The methane today is the greenhouse gas which is quite powerful. Pyrrolysine is the twenty-second amino acid of proteinogenic type.


    Proline is the non-essential amino acid with an aliphatic side chain. It is formed in our body from the other amino acids. It is non-polar and is hydrophobic. It has a secondary alpha amino group. It has codons CCA, CCC, CCU and CCG. Proline was obtained from casein in the year 1901. It is one of the amino acids which is soluble in alcohol. Proline exists in the form of cis configuration in the body. It also contains the pyrrole ring in it.

    amino acids proline


    It is not so needed to be obtained from the food as it is itself formed within our body. But it is richly present in the meat.


    Proline amino acid is formed from glutamate amino acid. The glutamate undergoes cyclization and reduction reaction and generates the proline amino acid. Many enzymes take place in this reaction. These include glutamate dehydrogenase enzyme, glutamate 5 kinases, pyrroline 5 carboxylate reductase and the glutamate 1 kinase enzyme.


    • Proline gives rise to glutamic acid which is an important amino acid. This glutamic acid then gives rise to very important compounds such as glutathione, glutamine, gamma-aminobutyric acid, alpha-ketoglutarate etc.
    • Proline is also converted to hydroxyproline by a post-translation reaction that is after it has been incorporated into the protein molecule.
    • The hydroxyproline is an important component of the collagen. So proline indirectly improves the texture of our skin. Collagen also has many functions. Since it allows the damaged cartilage to heel early and also it is important for the vertebra and joints as it cushions the both.
    • Failure of collagen synthesis due to some genetic defects leads to many disorders, for example, the Ehlers-Danlos syndrome. Other diseases due to an abnormal structure of collagen include osteoarthritis and osteogenesis imperfect disease.
    • This hydroxyproline also gives rise to the formation of glyoxylic acid as well as the pyruvic acid in our body. The glyoxylic acid then forms oxalic acid and the pyruvic acid then gives rise alanine amino acid.
    • Proline is interchangeable with the ornithine, thus it can lead to the formation of urea as well. On the other hand, ornithine has also been found to form proline.
    • Proline is essential for the normal health of the tendons, joints and the muscles.
    • Proline is also utilized in making a number of beneficial drugs.
    • It has also been seemed to maintain the normal health of our muscle tissues.

    Thus, proline is also an important amino acid. Its supplements are also available in the market. These are especially important in those people who are suffering from diseases due to collagen deficiency and also in those suffering from skin disorders and injuries.


    Phenylalanine is the amino acid with the aromatic side chain and is relatively polar.  It is one of the essential amino acids which means it should be provided to the body from diet.

    This amino acid also absorbs ultraviolet light and strong a absorbance of light by protein is at 280 nm. This property is used to detect and measure proteins. Its codons are UUU and UUC and are coded for by DNA as well. The codons are discovered by Heinrich Matthaei and Marshall Nirenberg in 1961. It has three forms: D-phenylalanine, L-phenylalanine, DL-phenylalanine.

    amino acids phenylalanine


    It is mostly found in protein-rich foods.

    • Animal sources: Fish, poultry, dairy foods, cheese, yogurt, beef etc.
    • Plant sources: They contain avocado, almonds, lima beans, seeds peanuts, nuts, and tofu etc.

    It is also present in the breast milk of some mammals.

    Phenylalanine supplements are also available.


    • Phenylalanine gives rise to tyrosine which is one of the most important amino acids. This reaction is characterized by phenylalanine hydroxylase.
    • Tyrosine also gives rise to many different and essential products, for example, melanin, thyroid gland, and neurotransmitters like aldosterone, noraldosterone, and dopamine. So it is also involved in the central nervous system.
    • This amino acid has been seen to improve Parkinsonism symptoms such as walking difficulties, rigidity, difficulties in speech etc.
    • Phenylalanine crosses the blood-brain barrier and then it interferes with the formation of serotonin.
    • D-phenylalanine plays an important role in the treatment and relief of chronic pains.
    • It has also found useful in persons with vitiligo as it helps to strengthen the ultraviolet rays’ effect on them.
    • It may also be helpful in case of depression as it gives rise to tyrosine which produces neurotransmitters essential for depression removal.


    This amino acid is converted into many derivatives that are excreted in the urine. These are phenyl acetic acid, phenyllactic acid, hydroxyphenylpyruvic acid and hydroxyphenylacetic acid. However, this is the normal pathway of this amino acid and it becomes quantitively more important when phenylalanine does not undergo in its major pathway which is its conversion to tyrosine.


    Phenylketonuria is the disease of an inborn error of amino acid metabolism. This disease is caused by a deficiency of phenylalanine hydroxylase. Symptoms of the central nervous system arise which include seizures, failure to walk and talk, microcephaly, hyperactivity and failure to grow. Hypopigmentation also occurs in this disease. Early diagnosis of phenylketonuria is important because it is possible to treat early by means of diet. Neonatal and antenatal screening is possible. Treatment includes lifelong phenylalanine-restricted diets.

    Maternal Phenylketonuria

    When women suffering from this disease and not on restricted diet become pregnant, her offsprings are then affected with maternal phenylalanine syndrome. The high level of this amino acid causes mental retardation, microcephaly and congenital heart diseases in the baby. So its level should be controlled prior to conception. Phenylalanine thus is a very important amino acid. Nowadays it has been used to produce certain medicines and nutritional supplements synthetically.


    Methionine is the uncharged polar amino acid. It is an essential amino acid as it is not synthesized in our body and must be provided through food. It is also the sulfur-containing amino acid. It was isolated from casein in 1922. It has a single codon which is AUG.

    amino acids methionine


    Methionine is derived from the animals as well as plants sources.

    Animal Sources: These include chicken meat, fish, dairy products, cheese, yogurt, and eggs etc.

    Plant sources: These include lentils, garlic, onion, seed, beans, oats, cereals, wheat germs, corn, almonds, and rice.


    Methionine being essential is not manufactured in our body. It is synthesized in the plants and some microorganism from aspartic acid with the help of enzymes which are aspartokinase, homoserine O-transsuccinylase, homoserine dyhydrogenase, cystathine beta-lyase, homoserine dehydrogenase, methionine synthase, and cystathione synthase.etc.

    It is also regenerated by the reverse process from the homocysteine with the help of an enzyme, the methionine synthase.


    • Methionine gives rise to cysteine by converting into S-adenosyl methionine which further converts into adenosine and homocysteine by hydrolysis. Homocysteine then reacts with serine and results in the formation of cystathione which then finally form cysteine.
    • Methionine plays role in maintaining our skin and nails free of problems
    • It is also important in the formation of carnitine, lecithin, taurine, phosphatidylcholine and some phospholipids.
    • Methionine also plays an important role in the break down of fats. This results in prevention of accumulation of fats in the blood vessels. Thus in case of its deficiency in the body, it may dispose the arteries to arteriosclerosis.
    • It has also been found to act as an antioxidant as its sulfur group removes the free radicals which are harmful to our various organs.
    • It is also beneficial in preventing lethargy and sluggishness.
    • Methionine has been found useful in treating chronic diseases like arthritis, depression and chronic liver diseases.
    • It increases the production of lecithin by the liver which helps to lower the cholesterol level in the body.
    • It has also been found in assisting our digestive system where it acts as a chelating agent for heavy metals and results in their removal from the body.
    • Methionine along with other amino acids also forms creatine which is an important constituent of the muscles and provide them strength.
    • If it’s not taken in a proper amount, its deficiency may lead to skin problems. The common problems are dermatitis, fatigue, slow growth, fatty liver or edema.
    • People suffering from pancreatitis, liver diseases or Parkinsonism may get benefits from methionine amino acid.
    • It is also found to promote estrogen hormone, therefore women taking contraceptives pills can use it as well.

    Thus, a good intake of methionine amino acid keeps you healthy and active.


    Lysine is the amino acid with the basic side chain. It is an essential amino acid as it is not manufactured in our body so it needs to be supplied from the diet to our body. It was first obtained from casein in 1889. It has AAA and AAG codons. It is a strong base with a positive charge and is ketogenic.

    amino acids lysine


    It is present in wide variety of foods.

    • Animal Source:  The animal sources of lysine are chicken, beef, milk, catfish, eggs, cheese etc.
    • Plant sources: Some of the plant sources are pulses, chickpea, kidney beans, yeasts, lentils, soybeans, potatoes, navy beans etc.


    Lysine is not synthesized in our body. In plants, it is synthesized from aspartate with the help of different enzymes. These are aspartokinase, Diaminopimelate epimerase, succinyl diaminopimelate aminotransferases, diaminopimelate decarboxylase, succinyl diaminopimelate desuccinylase etc.


    • Being ketogenic it gives rise to acetyl CoA which is an important constituent of the citric acid cycle. It also produces hydrolysine by post-translational modification. Hydrolysine is an important part of collage and provides stability for collagen crosslinks.
    • Lysine via its effects on serotonin receptors present in the gastrointestinal tract has an anxiolytic action. These serotonin receptors lead to anxiety induced disorders due to their hyperstimulation in the intestinal tract but lysine acts to reduce their stimulatory effect. It has also been found essential in the growth and development of bones, especially in the children.
    • It is also utilized in our body for producing antibodies, enzymes, hormones, and collagen. It also plays role in wound healing and repair. It maintains the nitrogen balance in the body. It increases the muscle mass and is therefore good food for those who are recovering from some injuries or from any surgery. It maintains the health of blood vessels.
    • Lysine has been found a wonderful weapon in combating infections as well as in reducing their outbreaks. It is found to be good for simplex herpes viral infection and for cold sores as it helps in healing the infections early and quickly. It also reduces the absorption of arginine amino acid since arginine is thought to be utilized by herpes virus for its replication. Lysine supplements are also in use for this reason as they are thought to prevent the eruptions of shingles which is causes by varcella zoster virus when the body’s immunity is low.
    • If people are not taking proper diet or diet less of lysine, there are possibilities that they can face such problems as hair loss, inability to concentrate well, bloodshot eyes, growth retardation, problems in reproductive systems, irritability, weight loss and all the time feeling of fatigue and lethargy.
    • One of the important physiological roles of this amino acid is that it increases the calcium absorption and decreases its excretion through urine. So by this thing, it indirectly increases the strength of bones and prevents them from bone fractures.
    • Lysine is also used in a number of animals feed. Lysine supplements are available in the form of capsules, tablets, liquid, and creams. These should be taken into care especially for people who are suffering from any liver and kidney diseases.


    Leucine is the branched-chain amino acid with a non-polar aliphatic side chain. It is an essential amino acid as it cannot be synthesized by the body. So it must be obtained from the foods or diets. It has UUG, UUA, CUC, CUU and CUG codons. Leucine is a ketogenic amino acid.

    amino acids leucine


    It is found in foods containing proteins. Its sources are:

    • Animal sources: Meat, chicken, poultry, fish, seafood, dairy products like cottage cheese etc
    • Plant sources: Whole lentils, brown rice, nuts, soy flour, whole wheat, beans, sesame seeds and peanuts etc.


    Since leucine is not formed in our body but it is synthesized in the plants and some microorganism. In them, it is formed from pyruvate by using following enzymes namely, acetolactate synthatase, dihydroxyacid dehydratase, acetohydroxy acid isomeroreductase, isopropylmalate isomerase and synthase along with leucine aminotransferase.

    In the human body, it has been found to be a major component of buffer proteins, austacin, and ferritin.


    • Leucine is exclusively ketogenic amino acid as it gives rise to ketoacyl CoA which is converted into acyl CoA derivatives which include HMG-CoA. This HMG-CoA is important as it takes part in the synthesis of cholesterol. It can also be broken down to acetoacetic acid and acetyl CoA.
    • Leucine is essential in regulating blood glucose level as well as in the growth and repair of bones, skin, and muscles.
    • It stimulates the synthesis of muscle proteins.
    • It also results in the production of growth hormones and it also burns visceral fats which are located in the deeper layers of the body and are least responsive to dieting and exercises.
    • Leucine also prevents the break down of muscle proteins which occurs during trauma, the stress of severe kind, during starvation or recovery from surgery.
    • It is also useful for early wound healing.
    • Patients suffering from phenylketonuria can take leucine which has been found beneficial to them.


    An excess intake of leucine results in the development of pellagra which is characterized by 3 D’s namely, Dermatitis, diarrhea, and death.

    Its high intake has also been found to damage the liver and kidney functions as a result of increased production of ammonia.

    A disease known as branched chain ketoaciduria or maple syrup urine disease has been found due to the failure of metabolism of three amino acids which are leucine, isoleucine, and valine. The failure occurs due to the deficiency of an enzyme branched chain keto acid dehydrogenase that is responsible for decarboxylation of these three amino acids. This disease is characterized by dehydration, vomiting, feeding problems in the baby and metabolic acidosis. There is a characteristic maple syrup odor in the urine, hence named maple syrup urine disease. If it is not treated, it will lead to mental retardation, physical disability, and even the death.

    In a nutshell, leucine is an important amino acid. It is also available in the form of supplements in the market. These supplements can be taken with valine and isoleucine for better results.


    Isoleucine is an essential amino acid so it needs to be provided by the food to our body. It has aliphatic side chain and is non-polar. It is also hydrophobic. It has AUU, AUA and AUC codons. Isoleucine along with threonine has a chiral side chain. There are four stereoisomers of isoleucine along with two diastereomers. It is glucogenic as well as ketogenic amino acid.

    amino acids isoleucine


    It is found in the following sources;

    • Animal Sources: Some of the isoleucine animal sources are meats, chicken, fish, turkey, lamb, egg, dairy products, cheese etc
    • Plant Sources: Some of the plant sources are soy protein, nuts, whole lentils, seaweeds, peanuts etc.


    Isoleucine is not synthesized in our body. It must be ingested from foods. In a plant, it is synthesized from the pyruvate and alpha-ketoglutarate with the help of enzymes namely, dihydroxy-acid dehydratase, acetolactate synthase, valine aminotransferase and acetohydroxy acid isomeroreductase.


    • Isoleucine undergoes transamination and forms alpha-keto acid which is then converted into aceyl-CoA derivatives and which then gives rise to propionyl-CoA and acetyl-CoA. The propionly-CoA is converted to L-methylmalonyl-CoA and which then forms succinyl-CoA. These play role in the citric acid cycle then.
    • Isoleucine has the ability to increase strength and also heel and repair muscle tissues. 
    • It also promotes healing by clotting at the site of injury.
    • It also prevents muscle proteins break down when exercising. 
    • Isoleucine produces many compounds in our body which provides energy to us.
    • Isoleucine is also needed in children for their growth.
    • It also stabilizes and regulates blood sugar levels. This occurs as isoleucine is converted into glucose in the liver which then enters into the blood.

    Isoleucine deficiency produces symptoms that are just like hypoglycemic symptoms for example in its deficiency a person may experience confusion, irritability, fatigue, depression, dizziness, headaches etc.

    Isoleucine genetically altered metabolism leads to a disease called maple syrup urine disease. So these patients should avoid isoleucine supplements.

    Isoleucine is also available in supplements and these supplements are helpful in the prevention of muscle wasting and promotion of tissue repair after surgery or trauma. These also increase muscle mass.


    Histidine is the glucogenic amino acid with a basic side chain. It is a weak base. After being incorporated in a protein molecule, histidine may show either a positively charged or negatively charges side chains which are determined by the ionic environment provided by the proteins. Histidine is an essential amino acid which needs to be provided by the food to our body. It is present in the DNA. It is proteinogenic amino acid and. CAC and CAU are its codons. Histidine contains imidazole functional group which makes it a participant in an enzyme-catalyzed reaction.

    amino acids histidine


    Following are the histidine sources:

    • Animal sources: Meat, poultry, eggs, fish, dairy products like milk, cheese etc
    • Plant sources: Rice, rye, and wheat are some of the plant sources of histidine amino acid.


    It is produced in the body as a result of a breakdown of muscle protein. Histamine is also released by chemical and mechanical stimuli in our bodily. Some of the drugs also result in the release of histamine. It is also released by tissue injury and burns.


    Histidine is the precursor of a very important amine called “histamine” which is formed by its decarboxylation in the presence of enzyme histidine decarboxylase. In the body, histamine performs a number of functions. Histamine has four receptors in the body. These are H1, h3, H3, and H4. Some of its functions are as follow.

    • Histamine is released during immune reactions and it brings about type 1 allergic reactions.
    • In the lungs, histamine causes bronchoconstriction to a slight extent in normal person but markedly in asthmatic patients.
    • Its release leads to vasodilation of arterioles and pre-capillary sphincters, these results in decrease peripheral resistance and therefore severe fall of both systolic and diastolic blood pressure.
    • It also causes increased permeability of vessels and this leads to urticaria and laryngeal edema.
    • Histamine acts directly on the cardiac pacemaker and this causes an increase in heart rate. Increase in heart rate also occurs due to the reflex response of hypotension.
    • In the gastrointestinal tract histamine causes intense stimulation of gastric hydrochloric acid secretion through h3 receptors
    • Due to histamine administration in pregnant women, it results in uterine contraction.
    • Smooth muscle of gastrointestinal tract also undergoes contractions after histamine administration.
    • Histamine also plays an important role in our central nervous system. It plays a role as a neurotransmitter and neuromodulator.

    The histaminergic neurons are present in the posterior hypothalamus whose axons project to all areas of the brain. These neurons seem to play role in pain threshold, arousal, sexual behavior, blood pressure and regulation of drinking. It has been seen that they also play role in the regulation of secretion of several anterior pituitary hormones.

    Histidine is important for growth and repair of the tissues and also in the maintaining myelin sheath functional. Histidine also plays role in the synthesis of both the red blood cells and white blood cells. Histidine is very important in infants and its deficiency in them leads to eczema which is a form of dermatitis.

    Histidine supplements are also available in the market these days.


    Glycine amino acid is non-essential amino acid as it is synthesized in our body mainly in the liver from other amino acids. It is non-polar and has an aliphatic side chain. Glycine is hydrophobic and it tends to cluster together with other hydrophobic amino acids. It is the smallest amino acid found in proteins and DNA. It has following codons, namely GGC, GGG, GGU and GGA. Glycine was first isolated from gelatin in the year of 1820. This amino acid is sweet in taste and colorless.

    amino acids glycine


    Glycine is mainly found in protein rich-food.

    • Animal sources: Fish, dairy foods, meat, cheese etc
    • Plant sources: beans, soybean etc

    It is also found in large amount in silk fibroin. In our body, it is present in skin, muscles and in collagen.


    In our body glycine is synthesized from serine which is also an amino acid. Serine gives rise to glycine by the reversal of serine hydroxymethyl transferase reaction.


    • Glycine is the part of glutathione which is a coenzyme involved in many biochemical reactions. The important function of glutathione is that it helps in the maintenance of the cell integrity by protecting –SH group of hemoglobin, catalase, and lipoproteins of the cell membrane. So glycine has an important antioxidant action.
    • It takes part in the manufacturing of purine, heme, and creatine.
    • It conjugates with benzoic acid in the liver and forms hippuric acid which is then excreted in the urine; this is called a detoxicating reaction. It also conjugates with many other drugs and their derivatives that contain carboxyl group which makes them water soluble and excretable in the urine.
    • Glycine can also be converted to serine by the addition of hydroxymethyl group and this reaction is catalyzed by an enzyme called serine hydroxymethyl transferases which further requires the coenzymes to carry out the reaction.
    • Glycine also has an ability to conjugate with cholic acid and chenodexoycholic acid, both of which are primary bile salts.
    • It also plays a role in the absorption of calcium in the body.
    • Glycine amino acid can be oxidized to glyoxylic acid catalyzed by an enzyme glycine oxidase. Glyoxylic acid undergoes further oxidation to form formic acid and oxalic acid. Formic acid takes part in one-carbon metabolism while the oxalic acid is excreted in the urine.
    • The most important role of glycine is in the central nervous system where it acts as a neurotransmitter of inhibitory in nature.
    • Glycine cleavage enzyme which is also called glycine synthase cleaves glycine to carbon dioxide ammonia and methylene group oxidatively. The methylene group then takes part in one-carbon metabolism.
    • This amino acid is also found to be produced in the prostate fluid present in males so it is considered to be important for prostate normal functioning.
    • It also enables our body to repair damaged tissues.
    • Glycine is glucogenic so it also provides glucose which is necessary for energy.

    Thus, glycine plays many vital roles. It is now available in dietary supplements as well which are found helpful in the treatment of fatigue and lethargy.

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