PURIFICATION AND CHARACTERIZATION OF CATHEPSIN-B FROM THE WHITE MUSCLE OF CHUM SALMON, ONCORHYNCHUS-KETA

1. 1. Cathepsin B from the white muscle of chum salmon (Oncorhynchus keta) in spawning migration was purified to homogeneity by a series of chromatography on DEAE-Sephadex, Thiopropyl-Sepharose and Sephadex G-100. 2. 2. The molecular weight of cathepsin B isolated was estimated to be 28,000 by the SDS-PAGE method and its isoelectric point to be 4.9 by isoelectric focusing. 3. 3. The cathepsin B had a pH optimum of 5.7, required a thiol-reducing reagent for activation, and was inhibited by thiol-protease inhibitors. 4. 4. The Km and kcat values for Z-Phe-Arg-MCA were determined to be 0.161 mM and 238 s-1, and those for Z-Arg-Arg-MCA were 0.540 mM and 95 s-1, respectively. 5. 5. The cathepsin B acted on oligopeptide substrates mainly as a dipeptidyl carboxypeptidase. © 1990.