Kinetic mechanism of β-xylosidase from Trichoderma reesei QM 9414

β-Xylosidase is a key enzyme in the hydrolysis of xylobiose to d-xylose. The enzyme was purified from cultures of Trichoderma reesei QM 9414 grown on wheat straw as a carbon source. β-Xylosidase shows the highest catalytic efficiency towards xylobiose and the highest affinity for 4-methylumbellyferyl-β-d-xylopyranoside, an arylxyloside whose aglycone is very hydrophobic. Studies of inhibition by products on the p-nitrophenyl-β-d-xylopyranoside kinetics and by an alternative product, 4-methylumbelliferone, supports an Ordered Uni Bi mechanism for the reaction catalysed by β-xylosidase. Competitive inhibition by a product analog, D-glucono-1,5-lactone is also compatible with the proposed mechanism.