Purification and Characterization of a Chymotrypsin‐Like Enzyme from Sperm of the Sea Urchin, Hemicentrotus puleherrimus

A chymotrypsin‐like enzyme has been purified from sperm of the sea urchin, Hemicentrotus pulcherrimus, using tryptophan methyl ester (TrpOMe) linked to Sepharose 4B as an affinity column for chromatography and gel filtration. The isolated enzyme preparation is homogenous in sodium dodecylsulfate/polyacrylamide gel electrophoresis, the estimated molecular weight being 18500‐19000. This enzyme hydrolyses N‐acetyl‐l‐tyrosine ethyl ester (AcTyrOEt) and N‐benzoyl‐l‐tyrosine ethyl ester (B_zTyrOEt); the optimal pH is 8.0. It does not hydrolyse N‐benzoyl‐l‐arginine ethyl ester, N‐α‐toluenesulfonyl‐l‐arginine methyl ester, N‐α‐benzoyl‐dl‐arginine‐p‐nitroanilide, hippuryl‐l‐arginine or hippuryl‐l‐phenylalanine. The Michaelis constants for AcTyrOEt and B_zTyrOEt are 0.05 mM and 0.0106 mM, respectively. The enzyme activity is inhibited completely by phenyl‐ methylsulfonyl fluoride (PhMeSO₂F), chymostatin and l‐I‐tosylamido‐2‐phenylethyl chloromethyl ketone (TosPheCH₂Cl), and partially by soybean trypsin inhibitor and N‐7alpha;‐p‐tosyl‐l‐lysine chloromethyl ketone (TosLysCH₂Cl). The enzyme is activated by CaCl₂, MgC1₂, NaCl and KCl, and loses its activity in 5 min at 67°C. It digests the jelly coat and vitelline layer, not the fertilization membrane. The microvilli of unfertilized eggs elongate and decrease in number as the vitelline layer lyses. The vitelline layer lytic activity is inhibited completely by PhMeSO₂F, TosPheCH₂Cl, and chymostatin, and partially by soybean trypsin inhibitor, TosLysCH₂C1, and αl‐antitrypsin. We have confirmed by transmission electron microscopy that our chymo‐trypsin‐like enzyme completely digests the vitelline layer. A result implying release of this enzyme from the acrosome vesicle is also reported