2種のβ-キシロシダーゼによるキシロースの縮合反応の比較

概要

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The kinetic characterization of two fungal (Aspergillus niger and Malbranchea pulchella) β-xylosidases reveals "product specificity" in the condensation reaction of xylose. The specificity of xylodisaccharide production in the condensation reaction yields more variation for the M. pulchella enzyme than for the A. niger one. Of the products, β-1,4-xylodisac-charide is produced most in the reaction of both enzymes. A simple mechanism with forward (condensation) and reverse (hydrolysis) reactions is assumed and the rate constants for the forward reactions of the respective β-linked xylodisaccharides are experimentally determined as well as the equilibrium constants. The rate constants for the reverse reactions are estimated from these equilibrium and rate constants, and found to have smaller values than those observed in the initial velocities of the hydrolysis, inferring inhibition of the reaction with a high concentration of xylose. Comparison of the actual time course in xylodisaccharide production with that obtained by a computer simulation for this simple mechanism implies that the reaction mechanism of the M. pulchella enzyme comprises the condensation and hydrolysis reactions, while the mechanism of the A. niger enzyme further includes the reaction producing xylotrisaccharide.
東京聖栄大学の論文
1993-12-20