Hydrolysis of dipeptides by human and ovine placentas

Human and ovine placental tissue homogenates were assayed for dipeptidase activity in vitro. Glycyl-L-leucine, L-leucyl glycine, glycyl-L-lysine, and L-lysyl glycine were hydrolyzed by placental homogenates. The pH optimum for the reaction was 8.0. The relationship between enzyme activity and concentration was linear for placental homogenate concentrations between 0.01 and 0.10 mg protein/ml of reaction mixture. Enzyme activities were 1.92 +/- 0.12 (S.E.) micromoles/min/mg protein for hydrolysis of glycyl-L-leucine, 0.34 +/- 0.06 (S.E.) micromoles/min/mg protein for hydrolysis of glycyl-L-lysine by human placenta, and 2.79 +/- 0.80 micromoles/min/mg protein and 0.41 +/- 0.25 micromoles/min/mg protein, respectively, by ovine placenta. The infusion of glycyl-L-leucine into the uterine artery of unstressed catheterized pregnant ewes yielded increased concentrations of both component amino acids in uterine venous blood and of leucine in umbilical venous blood.