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.