PURIFICATION AND CHARACTERIZATION OF A CATHEPSIN B-LIKE ENZYME FROM MACKEREL WHITE MUSCLE

A cysteine protease was purified from the white muscle of common mackerel Scomber japonicus by ammonium sulfate fractionation and successive column chromatography. The final enzyme preparation appeared to be homogeneous on polyacrylamide gel electrophoresis. The purified enzyme hydrolyzed Z-Arg-Arg-MCA, but not Z-Phe-Arg-MCA. The molecular mass of the enzyme was estimated to be 55 kDa by gel filtration and have a pH optimum of 5.5. The enzyme was activated by sulfhydryl compounds such as dithiothreitol and cysteine. The enzyme was strongly inactivated by TLCK, TPCK, antipain, leupeptin, and E-64. Consequently, we concluded that the enzyme is a cathepsin B-like enzyme because of its substrate specificities.