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.