GLYCINE IS NOT FORMED THROUGH THE AMINO TRANSFERASE REACTION IN HUMANOR 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 a ctivity of alanine:glyoxylate aminotransferase enzyme was measured in placentae from normal term human pregnancies and placentae from rats a t day 20 of gestation. There was no detectable enzyme activity in eith er human or rat placentae, although activity was measured in rat liver . It is concluded that in the placenta glycine is only formed from ser ine through the activity of serine hydroxymethyl transferase enzyme, w hich uses folate as a cofactor, because there are no other known metab olic pathways for endogenous glycine production. (C) 1998 W. B. Saunde rs Company Ltd.