Strong inhibitor of acrosin in male and/or female genital tract. Also inhibits trypsin (By similarity). As a strong inhibitor of acrosin, it is required for normal spermiogenesis. It probably hinders premature activation of proacrosin and other proteases, thus preventing the cascade of events leading to spermiogenesis defects (By similarity). May be involved in the regulation of serine protease-dependent germ cell apoptosis (By similarity). It also inhibits trypsin (By similarity). More abundant in epididymis than in testis.