A Proteinase and Proteinase Inhibitor of Mammalian Sperm Acrosomes

Acrosomal extracts of epididymal boar and epididymal and ejaculated rooster spermatozoa possess high proteinase (acrosin) activity. Less activity is present in extracts from ejaculated human, monkey, and ram sperm or epididymal rabbit, stallion, and ram sperm, and virtually none can be found in extracts at neutral pH of ejaculated sperm of the rabbit, bull, stallion, and boar or epididymal sperm of the bull, guinea pig, rat, and hamster because the acrosin is blocked by complexing with an acrosin inhibitor. Evidence for an acrosin-acrosin inhibitor complex in sperm acrosomal extracts was provided by testing for complex dissociation and formation at acidic and basic pH, respectively, then demonstrating the inhibitor in the extracts by: (1) trichloracetic acid (TCA) precipitation of acrosin leaving the inhibitor in solution and (2) separation of enzyme and inhibitor by Sephadex chromatography after dissociation at acidic pH. With the possible exception of boar epididymal sperm, all ejaculated and epididymal mammalian sperm tested possessed the complex although the amounts varied among species. The complex does not occur in extracts of rooster sperm acrosomes. Extracts of epididymal sperm acrosomes of the rabbit, boar, and stallion, but not the bull, ram, and rooster, possessed significantly more acrosin activity than the corresponding extracts of ejaculated sperm acrosomes suggesting that inhibitor is added to the acrosin of the first three species during ejaculation. It is likely that the acrosin inhibitor is removed from mammalian spermatozoa during residence in the female genital tract.