Purification and Properties of β-Glucosidase from Aspergillus terreus

Abstract

A β-glucosidase (EC 3.2.1.21) from the fungus Aspergillus terreus was purified to homogeneity as indicated by disc acrylamide gel electrophoresis. Optimal activity was observed at pH 4.8 and 50°C. The β-glucosidase had K m values of 0.78 and 0.40 mM for p -nitrophenyl-β- d -glucopyranoside and cellobiose, respectively. Glucose was a competitive inhibitor, with a K i of 3.5 mM when p -nitrophenyl-β- d -glucopyranoside was used as the substrate. The specific activity of the enzyme was found to be 210 IU and 215 U per mg of protein on p -nitrophenyl-β- d -glucopyranoside and cellobiose substrates, respectively. Cations, proteases, and enzyme inhibitors had little or no effect on the enzyme activity. The β-glucosidase was found to be a glycoprotein containing 65% carbohydrate by weight. It had a Stokes radius of 5.9 nm and an approximate molecular weight of 275,000. The affinity and specific activity that the isolated β-glucosidase exhibited for cellobiose compared favorably with the values obtained for β-glucosidases from other organisms being studied for use in industrial cellulose saccharification.