Purification and tissue/species dependence of the specificity of buffalo kidney cathepsin B

A simple purification scheme was developed for isolation and purification of cathepsin B from buffalo kidney. The use of CM-Sephadex and chromatofocusing helped in better and simultaneous separation of cathepsin B, H and L. As judged by PAGE and SDS-PAGE studies, the enzyme was found to be pure on the basis of charge and had a molecular mass of 25.5 kDa. The amino acid composition, number of free sulfhydryl groups and other major physico-chemical properties of the purified enzyme were similar to the properties reported for cathepsin B from other sources/tissues. However, the NH2-terminal amino acid residue of the enzyme was found to be Ala as against Leu reported from other tissues/species. The total carbohydrate content was also found to be significantly lower (3.6%) as compared to 7.0-7.6% reported for the enzyme from other sources. Thiol reducing compounds activated the enzyme whereas thiol blocking compounds inhibited it. The buffalo kidney enzyme hydrolyzed Z-Phe-Arg-MCA (Vmax/K(m) = 17.1) as the most efficient substrate followed by Z-Arg-Arg-MCA, BANA and BAPNA. Among the protein substrates, goat hemoglobin (Vmax/K(m) = 874) was found to be the most preferred. Rabbit muscle aldolase, usually considered to be a good substrate for cathepsin B, proved to be a poor substrate for this enzyme; only 25-30% inactivation of aldolase was observed. Antibodies raised against the enzyme recognised only cathepsin B and did not have any cross reactivity with cathepsin H or L from the same or different sources. These differences in the properties of the buffalo kidney enzyme vis-a-vis the same enzyme from other tissue/species have been attributed to specialized function of cathepsin B in diversified tissues.