Influence of Molecular Structures of Substrates and Analogues on Taka-amylase A Catalyzed Hydrolyses: III. Inhibition by 2-Deoxy-D-glucose and Methyl α-D-Glucoside: Change in Inhibition Type with Substrate Chain Length*

Abstract

1. The inhibitory effects of 2-deoxy-D-glucose, methyl α-D-glucoside and D-gluco-samine on the hydrolytic reaction catalyzed by Taka-amylase A [EC 3.2.1.1] were studied at 25°C and pH 5.3 using phenyl-α-maltoside and linear oligosaccharides as substrates. These analogues were previously reported to inhibit the hydrolysis of phenyl α-maltoside noncompetitively (1). 2. In inhibition studies, with a mixture of the analogues which inhibited hydrolysis of phenyl α-maltoside noncompetitively these analogues were found to compete with each other for the same site (termed the site N) on the enzyme. 3. In similar studies with a mixture of a noncompetitive inhibitor (2-deoxy-D-glucose or methyl α-D-glucoside) and a competitive inhibitor (D-glucose or D-xylose) no interaction was detected between the site N and the binding site of the competitive inhibitors. 4. However, when the naturel linear oligosaccharides, maltotetraose and malto-heptaose are used as substrates, the analogues which inhibited hydrolysis of phenyl α-maltoside noncompetitively were found to exhibit competitive inhibition. The location of the site N in the specificity region of this enzyme was proposed on the basis of the effect of the chain length of linear substrates on this alteration of inhibition type, and on previous results on subsite affinities (2).