The activation of proacrosin in spermatozoa from ram, bull and boar

Abstract

Acrosin activity was estimated in fractions from washed ram, bull and boar spermatozoa that had been disrupted using a Stansted Cell Disruptor. When p-aminobenzamidine was included in the medium during disruption, all the acrosin (acrosomal proteinase, EC 3.4.21.10) was recovered as its inactive zymogen form, proacrosin. But if spermatozoa were damaged before disruption, or were disrupted in the absence of p-aminobenzamidine, considerable amounts of active acrosin were detectable. It was concluded that conversion of proacrosin to acrosin takes place in spermatozoa only after the acrosome has been ruptured. In a sucrose medium, all the proacrosin was bound to the sperm heads. Conversion to acrosin took place readily with all components in a bound state. Using ram sperm heads, the conversion was found to be relatively insensitive to pH, proceeding rapidly above pH 6.5; the rate of conversion was not affected by physiological levels of Ca 2+, Mg 2+ or Zn 2+, although elevated ionic strength caused a solubilization of the acrosin activity and some slowing of the rate. Electrophoretic analysis revealed that several active forms of acrosin were involved, but the final product was a single stable form. Final levels of the active acrosin (expressed as μmol N-α- benzoyl- l-arginine ethyl ester utilised/min per 10 9 heads) were: ram 26.2; bull, 15.9; boar, 133.8. But active site titration revealed that these different levels were not reflected in the numbers of active enzyme molecules on the sperm head; boar acrosin appears to be about three times more active towards benzoyl-arginine ethyl ester than do the acrosins from the other species.