Steady-State Inhibitory Kinetic Studies on the Ligand Binding Modes of Aspergillus niger Glucoamylase

Abstract

Inhibitory activities of 1-deoxynojirimycin and gluconolactone on Aspergillus niger glucoamylase were studied in relation to the subsite structure of the enzyme. Although both of these inhibitors are considered to bind at subsite 1 of the enzyme active site, 1-deoxynojirimycin showed competitive type inhibition but gluconolactone was a mixed type (or noncompetitive type) inhibitor for the hydrolysis of p-nitrophenyl α-D-glucoside. The former type of inhibition suggested that the main binding mode of the substrate was productive, but the latter, nonproductive. A possible way of explaining these apparent inconsistent results is to assume that the main binding mode of the substrate is productive and gluconolactone forms a nonproductive ternary complex with the enzyme and the substrate. © 1999, Taylor & Francis Group, LLC. All rights reserved.