Kinetic properties of placental aminopeptidase A: N-terminal degradation of angiotensin II.

Purified placental aminopeptidase A cleaved N-terminal aspartic acid of Angiotensin II, and it was inhibited by amastatin. Amastatin and various angiotensin analogs having N-terminal dicarboxylic acid were potent inhibitors of the enzyme. Kinetic analysis indicated that amastatin, angiotensin II, the N-terminal tripeptide of angiotensin II, and aspartic acid were competitive inhibitors, with Ki values 1.25 X 10(-7) M, 2.40 X 10(-5) M, 2.67 X 10(-4) M, and 1.2 X 10(-3)M respectively. The enzyme was also inhibited by transition metals, such as Zn2+, Cu2+, Cd2+ and Ni2+. Serum aminopeptidase A activity progressively increased during the course of normal pregnancy.