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 inter-action was detected between the site N and the binding site of the competitive in-hibitors. 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 lo-cation 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 in-hibition type, and on previous results on subsite affinities (2).
