Purification and some kinetic properties of β-glucosidase from Aspergillus terreus NRRL 265

An intracellular beta-glucosidase (EC 3.2.1.21) from Aspergillus terreus NRRL 265 grown on whey permeate was purified to homogeneity as indicated by disc acrylamide gel electrophoresis with an apparent molecular mass of about 116 kDa. Optimal activity was observed at pH 5.0 and 60 degrees C. The beta-glucosidase had K(m) values of 2.5, 3.7 and 5.5 mM for p-nitrophenyl-beta-D-glucopyranoside (p-NPG), cellobiose and salicin, respectively. Glucose and glucono-delta-lactone were found to be competitive inhibitors with apparent K(i) of 13.6 and 1.9 mM, respectively, when p-NPG was used as the substrate. Different metal cations had little or no effect on the enzyme activity, while Ag(+) and Hg(2+) had an inhibitory effect when used at high concentrations. In addition, beta-glucosidase was found to be a glycoprotein containing 69% carbohydrate by weight and free from any myco-toxins. SH groups do not seem to play a role in the catalytic action of beta-glucosidase as addition of iodoacetate, reduced glutathione or mercaptoethanol did not affect the activity.