Purification and some properties of buffalo liver cathepsin B

Buffalo liver cathepsin B was isolated by acid extraction, ammonium sulfate fractionation, Sephadex gel filtration, DEAE-Sephadex chromatography and Sephacryl S-300 chromatography. The enzyme preparation was found to be homogeneous by gel filtration and SDS-polyacrylamide gel electrophoresis but could be resolved into two major and four minor protein bands on polyacrylamide gel electrophoresis in the absence of SDS. The enzyme showed catheptic activity against synthetic substrates such as BANA and BAPNA as well as against denatured hemoglobin. Various physico-chemical and enzymatic properties of the enzyme, such as molecular weight, Stokes radius, frictional coefficient, pH optimum, Michaelis constant, and Vmax, were determined. The values of these parameters were 27,500, 2.41 nm, 1.2, 6.5, 2.08 mM, and 42.4 units/mg, respectively. The hydrodynamic properties suggest a compact and globular conformation for this enzyme. Various compounds were tested for their influence on the activity of cathepsin B. Of these compounds, membrane phospholipids were found to increase significantly the activity of this enzyme. This increase in activity could be of physiological importance since the concentration of phospholipids is increased after endocytosis and autophagy.