An acrosin-acrosin inhibitor complex in ejaculated boar sperm

Acrosin (a proteolytic enzyme) activity is high in extracts of epididymal sperm acrosomes but low in extracts of ejaculated sperm acrosomes. This lower activity from ejaculated sperm has previously been postulated as resulting from the reaction of a seminal plasma proteolytic enzyme inhibitor with acrosin in the acrosome. Evidence is presented which demonstrates that an acrosin-acrosin inhibitor complex exists in extracts of ejaculated boar sperm acrosomes. Upon incubation at pH 3 the complex dissociates and the free enzyme is demonstrable with the use of the synthetic substrate, benzyl arginine ethyl ester (BAEE). The increase in activity from incubation at pH 3 does not result from zymogen activation. Epididymal sperm have the ability to pick up the protease inhibitor from solution. The fact that there is no excess of free acrosin nor of free inhibitor in extracts of ejaculated sperm acrosomes is further evidence for the existance of an acrosin-acrosin inhibitor complex.