Acrosin (ACR)

Acrosin is the major proteinase present in the acrosome of mature spermatozoa. It is a typical serine proteinase with trypsin-like specificity. It is stored in the acrosome in its precursor form, proacrosin. The active enzyme functions in the lysis of the zona pellucida, thus facilitating penetration of the sperm through the innermost glycoprotein layers of the ovum. In many species, it is shown that biosynthesis of acrosin is confined to the haploid phase of spermatogenesis. By indirect immunofluorescent techniques, Florke-Gerloff et al.  demonstrated that in man (pro)acrosin first appears in the haploid spermatids. Adham et al.  isolated a full-length cDNA clone for human proacrosin. The deduced amino acid sequence of human proacrosin in the proline-rich domain is different from the corresponding sequence of boar proacrosin.