Inhibition of human and bovine sperm acrosin by divalent metal ions. Possible role of zinc as a regulator of acrosin activity.

Human and bovine spermatozoa have been collected and washed repeatedly with isotonic saline to remove seminal plasma inhibitors and activate the acrosin. Then the acrosin activity of the cells was assayed with alpha-N-Benzoyl-DL-Arg-beta-naphthylamide (BANA). It was found that the surface-bound enzyme was not inhibited by high molecular weight inhibitors of trypsin but was markedly inhibited by low molecular weight trypsin inhibitors. Divalent metals (Zn++, Cu++, Hg++, Co++, Cd++) were all efficient inhibitors of acrosin on the washed cells. It was shown that the removal of zinc or copper from acrosin completely restored activity. It is proposed that the different levels of zinc in the male and female genital tract regulate acrosin activity. Aged cells released a soluble acrosin which was inhibited by serum and seminal plasma inhibitors of trypsin-like enzymes as well as by zinc ions in an identical manner to the surface-bound enzyme.