Studies on the Subsite Structure of Amylases. III. Inhibition by Gluconolactone of the Hydrolysis of Maltodextrin Catalyzed by Glucoamylase1 from Rhizopus niveus2

Abstract

Inhibition by gluconic acid-1: 5-lactone (gluconolactone) and phenyl α-glucoside of the hydrolysis of maltodextrin catalyzed by glucoamylase [EC 3. 2.1. 3] from Rhizopus niveus was investigated in relation to the subsite structure of the enzyme. Inhibition by gluconolactone was of the mixed type, whereas that by phenyl α-glucoside was purely competitive. These inhibition types were consistent with a theoretical prediction based on the assumption that gluconolactone and phenyl α-glucoside bind mainly to Subsites 1 and 2, respectively. The inhibitor constant of gluconolactone was determined to be 1.5 mM, which is in good agreement with the dissociation constant estimated by difference spectro-photometry (1.5 mM) (Ohnishi, M. et al, (1975) J. Biochem. 77, 695–703).