STUDIES ON ACROSIN. I. PURIFICATION AND CHARACTERIZATION OF BOAR ACROSIN

Acrosin was extracted from boar sperm and purified by Sephadex gel filtration and affinity chromatography on Phe-Phe-Arg Sepharose 4B in acidic condition. Its enzymic properties were characterized in comparison with trypsin. The oligopeptides with Arg at the carboxy-termini were used as the ligands for affinity chromatography. Phe-Phe-Arg adsorbed acrosin at pH 5 and released it at pH 3. To adsorb acrosin, it was found that the ligand should be longer than tripeptide with Arg in the carboxy-termini. Disc gel electrophoretogram of purified boar acrosin gave a broad band consisted from three fractions which hydrolysed N-α-benzoyl-arginine ethylester (BAEE). The pH optimum and inhibition spectra were similar to those of trypsin, however, the influence of urea on them were very different among each other. Calcium ion decreased Km for BAEE, and increased Ki of aprotinin. The kinetic analysis of acrosin for its substrate and products resulted that Km for BAEE was minimal at around pH 8 and maximal at pH 5, on the contrary, Ki of the product was low at pH 5, but progressively increased along the elevation of pH. The same tendency was observed for trypsin. From the attitudes on the affinity chromatographies and the pH profiles of kinetic parameters, it was concluded that the active sites of acrosin and trypsin were similar to each other.