Boar acrosin. I. Purification and preliminary characterization of a proteinase from boar sperm acrosomes.

Acrosin is a proteolytic enzyme used by sperm to digest a path through the zona pellucida of the ovum. In ejaculated sperm it is inactivated by a proteinase inhibitor from seminal plasma that also inhibits trypsin. This inhibitor is removed or inactivated during the residence in the female reproductive tract as a part of the capacitation process. The boar acrosin-inhibitor complex was partially purified using DEAE-cellulose chromatography. The complex was dissociated and the acrosin obtained in a highly purtied form by the use of Sephadex gel filtration at pH 3.0. The final preparations were judged to be homogeneous on the basis of chromatographic and electrophoretic criteria and showed a molecular weight of 30,000. Acrosin has a temperature optimum of 53”, an esterase optimum at pH 8.5, and a proteolytic optimum on azocasein at pH 8.7. The enzyme is quite stable at pH 3.0 but undergoes destruction at slightly alkaline pH. Purified acrosin is both activated and stabilized by calcium ions; however, it is not stable to freezing nor to freeze-drying and is inactivated by urea.