GLYCINE

Glycine consists of a single carbon molecule attached to an amino and a carboxyl group. Its small size helps it to function as a flexible li nk in proteins and allows for the formation of helices, an extracellul ar signaling molecule, recognition sites on cell membranes and enzymes , a modifier of molecular activity via conjugation and glycine extensi on of hormone precursors, and an osmoprotectant. There is substantial experimental evidence that free glycine may have a role in protecting tissues against insults such as ischemia, hypoxia, and reperfusion. Th is impressive catalogue of functions makes an interesting contrast wit h glycine's perceived metabolic role as a nonessential amino acid. Gly cine interconverts with serine to provide a mechanism for the transfer of activated one-carbon groups. Glycine has just been viewed as a con venient source of nitrogen to add to solutions of nutrients. Although this may have unexpected benefits when such solutions are used inclini cal practice, it does raise the specter of a possible confounding effe ct in experiments when glycine is added to control solutions to make t hem isonitrogenous.