Glicin

Glicin, known in English as glycine, is the simplest amino acid and the only standard amino acid that is achiral. It is a building block of proteins and occurs widely in nature. Glycine is considered nonessential for humans because the body can synthesize it, although it is also obtained from dietary protein.

Chemical and physical properties: Glycine has the formula C2H5NO2 and a molar mass of 75.07 g/mol. At physiological pH it exists mainly as a zwitterion, with a carboxylate and an ammonium group. Its side chain is a single hydrogen atom, which gives glycine its small size and flexibility and allows it to fit into tight spaces, such as the collagen triple helix. The pKa values are approximately 2.3 for the carboxyl group and 9.6 for the amino group.

Biological roles: Glycine is a constituent of virtually all proteins. It is especially abundant in collagen, where its small size facilitates tight packing. Glycine participates in the synthesis of heme, purines, creatine, and glutathione. In the central nervous system, glycine functions as an inhibitory neurotransmitter and also acts as a co-agonist at NMDA receptors, influencing excitatory neurotransmission.

Metabolism and sources: Glycine can be synthesized from serine via serine hydroxymethyltransferase and can be degraded through the glycine cleavage system. It is furnished by dietary protein and is found in high concentrations in foods such as meat, fish, dairy products, and legumes. It also appears in certain pharmaceutical and food formulations.

Safety and use: Glycine is used as a dietary supplement and generally regarded as safe for most people. High doses can cause gastrointestinal discomfort in some individuals, but there is no widespread toxicity associated with typical supplemental intakes.