Partial Purification and Characterization of Cathepsin D-Like and B-Like Acid Proteases from Surf Clam Viscera

Different proteases were isolated and purified from viscera of surf clam, Spisula solidissima. These proteases were similar to cathepsins D and B, with molecular weights of ?36,700 and ?17,400 daltons, respectively. Optimum activity of enzymes towards hemoglobin and casein occurred from pH 2.5–3.0 and temperature 44–46°C. Cathepsin D-like protease, a carboxyl protease, was insensitive to most protease inactivators, but extremely sensitive to pepstatin. Cathepsin B-like protease, a thiol protease, was activated by thiol-reducing agents and metal chelators, but was sensitive to many reagents such as iodoacetamide, Tosyl-phenylalanine chloromethyl ketone, Tosyl-lysine chloromethyl ketone, phenylmethanesulphonyl fluoride, leupeptin and heavy metals.