Glycine is not formed through the amino transferase reaction in human or rat placenta

The fetus has a substantial demand for glycine, which is satisfied in part by placental formation. The ability to form glycine through the activity of alanine:glyoxylate aminotransferase enzyme was measured in placentae from normal term human pregnancies and placentae from rats at day 20 of gestation. There was no detectable enzyme activity in either human or rat placentae, although activity was measured in rat liver. It is concluded that in the placenta glycine is only formed from serine through the activity of serine hydroxymethyl transferase enzyme, which uses folate as a cofactor, because there are no other known metabolic pathways for endogenous glycine production. (C) 1998 W. B. Saunders Company Ltd.