On the tissue/species dependence of cathepsin B isozymes

Characterization of cathepsin B from buffalo kidney and goat spleen showed the presence of isozymes in case of the goat spleen (GSCB-I and GSCB-II) whereas cathepsin B from buffalo kidney exhibited only one form (BKCB). The molecular weights determined by SDS-PAGE for GSCB-I, GSCB-II, and BKCB were 25.7, 26.6 and 25.5 kDa respectively. The kinetic parameters (Km and Vmax) of GSCB-I showed close similarities with BKCB against alpha-N-benzoyl-DL-arginine-2-napthylamide whereas GSCB-II was closer to the buffalo enzyme with regards to its activity against Z-Arg-Arg-MCA and Z-Phe-Arg-MCA. All the three enzymes had similar sensitivities towards urea, antipain and leupeptin. However, clear differences were observed in the inhibition patterns of the enzyme with iodoacetic acid and iodoacetamide. Differences in the kinetic, immunogenic and some catalytic properties of GSCB-I and II, which had similarities with regard to most of their physico-chemical properties, were considered to be due to the existence of two isozyme forms in goat spleen cathepsin B preparations. Absence of such a multiplicity in forms of the enzyme from buffalo kidney was accordingly attributed to the absence of cathepsin B isozymes in this species. These observations taken together therefore, indicate a probable species/tissue dependence of cathepsin B.