Glycine

Description

Glycine is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.

Glycine helps convert many potentially harmful substances including toxic phenolic materials such as benzoic acid (sodium benzoate) into harmless forms. It is important in the control of gluconeogenesis, or manufacture of blood sugar from protein in the liver. Inappropriate blood sugar control may be managed by increased glycine intake. Glycine is known to serve as a basic nitrogen source for the manufacture of many other amino acids and is useful in the synthesis of hemoglobin, glutathione, DNA, and RNA. Glycine has also been found to be important as a part of the brain neurotransmission pathway. It is recognized to be a neuro-inhibitory neurotransmitter along with GABA.

Supplemental use of glycine at levels of 1-3g per day is useful in the treatment of certain forms of bi-polar depression (manic depression). Some individuals have an inborn error of glycine metabolism, which means increased glycine intake can result in elevated glycine levels in the blood that manifest themselves as severe mental retardation in infants susceptible to this condition. This is a very rare genetic metabolism problem, but should be evaluated in any individual who is going to be supplemented with glycine.

Recommended Dietary Allowances

An RDA has not been established for glycine because it is a nonessential amino acid.

Humans have shown a high tolerance for glycine without any ill effects.

Food Sources

Glycine is a nonessential amino acid, which means it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.

Method of Action

Glycine serves as a neuroinhibitory neuromodulator in the central nervous system and works along with gamma-amino butyric acid and taurine. It relates to hyperexcitability of CNS neurons, thereby depleting them of potassium and chloride and reducing their ability to be stimulated.

Glycine is also used in the biosynthesis of hemoglobin, which is very important in maintenance of proper red blood cell integrity and oxygen-carrying capacity. Glycine can also be methylated to dimethylglycine (DMG), which is part of the one-carbon pathway allowing for the donation and acceptance of methyl groups.

The one-carbon pathway is extremely important for the synthesis of steroids such as the androgenic and estrogenic hormones as well as cortisone-like hormones. Glycine inhibits glutamine synthetase, thereby blocking the formation of glutamine from glutamate. It may, therefore, have some adverse impact upon ammonia detoxification.

Abstracts

References

Blackburn, G.L., Grant, J.P., Young, V.R., ed. Amino Acids Metabolism and Medical Applications.

Giordano, C., DeSanto, N.G., Rinaldi, S., De Pascale, C., & Pluvio, M., Histidine and Glycine Essential Amino Acids in Uremia", in Uremia: An International Conference.

Munro, H.N. & Crim, M.C. The Proteins and Amino Acids. Modern Nutrition in Health and Disease, eds: R.S. Goodhart & M.E. Shils, 6 ed. Philadelphia: Lea and Febiger, 1980.

Wada, Y., Tada, K., Takada, G., Omura, K., Yoshida, T., Kuniya, T., Aoyama, T., Kakui, T. & Harada, S. Hyperglycinemia Associated with Hyperammonemia: In Vitro Glycine Cleavage in Liver", Pediatr. Res., 6:622-5, 1972.

Winters, R.W., Heird, W.C., Dell, R.B., & Nicholson, J.F. Plasma Amino Acids in Infants Receiving Parenteral Nutrition. Clinical Nutrition Update--Amino Acids, eds. H.L. Greene, M.A. Holliday & H.N. Munro, Chicago: Am Med Assoc, 1977, pp. 147-54.

Young, V.R., Meguid, M., Meredith, D.E. & Bier, D.M. Recent Developments in Knowledge of Human Amino Acid Requirements. Nitrogen Metabolism in Man, eds: J.C. Waterlow and J.M.L. Stephen. London: Applied Science Pubs, 1981.