Effects of Low Molecular Weight Peptides and Divalent Cations on Degradation and Binding of Angiotensin II

Summary

The effects of peptide inhibitors (bestatin and amastatin) and divalent cations (Ca²⁺ and Co²⁺) on the velocity of Asp¹ liberation from angiotensin II (A-II) by human placental membrane fractions and binding of ¹²⁵I A-II to human placental membranes were tested at 22 °C and 4 °C. Asp¹ liberation was measured by high performance liquid chromatography. As expected, the degradation and binding of A-II were temperature sensitive, with both being at 4 °C than at 22 °C. While amastatin (10^-4M) and bestatin 10^-6M) significantly reduced the velocity of Asp¹ liberation from A-II to about 45%, amastatin (10^-4M) and bestatin (10^-4M) increased ¹²⁵I A-II binding to 125% and 130%, respectively. Ca²⁺ (10 mM)and Co²⁺ (10 mM) activated the velocity of Asp¹ liberation from A-II to 140% and 120%, respectively at 22 °C. Ca²⁺ (10-¹ M) and Co²⁺ (10 mM) also enhanced ¹²⁵I A-II binding about 130%. Previously we showed that the A-II degrading activity found in human placental membrane fractions is mainly due to aminopeptidases A and M. Since amastatin and bestatin are the specific inhibitors for aminopeptidases A and M, and since Ca²⁺ and Co²⁺ are the activators for aminopeptidase A and aminopeptidase M, respectively, it is conceivable that the enzymes regulate the levels of A-II and, therefore, that they may play an important role in the binding of A-II to human placental membrane fractions.

Degradation and Binding of Angiotensin II - Human Placenta - Amastatin - Bestatin - Ca²⁺ - Co²⁺ - Angiotensinase