Involvement of a trypsin-like activity in sperm penetration of zona-free mouse ova

The presence of trypsin inhibitors during insemination reduced penetration of zona-intact and zona-free mouse ova by capacitated sperm. This inhibition was dependent upon both concentration of inhibitor and sperm. Preincubation of gametes in inhibitors did not markedly influence their subsequent fertility, nor did it alter sperm motility. Trypsin inhibitors may exert an effect on penetration by interfering with the induction of the sperm acrosome reaction or with the process of sperm-egg fusion.