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.
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.