Studies on the substrate specificity of taka-amylase A. XIV. Preparation of 6-deoxy-6-halogenomaltotrioses and their hydrolysis by taka-amylase A.:XIV. Preparation of 6-Deoxy-6-Halogenomaltotrioses and Their Hydrolysis by Taka-Amylase A

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1. O-6-Deoxy-α-D-glucopyranosyl-(1→4)- O-α-D-glucopyranosyl-(1→4)-D-glucopyranose, O-6-chloro-6-deoxy-α-D-glucopyranosyl-(1→4)-O-α-D-glucopyranosyl-(l→4)-D-glucopyranose, O-6-bromo-6-deoxy-α-D-glucopyranosyl-(1→4)-O-α-D-glucopyrano syl-(1→4)-D-glucopyranose, and O-6-deoxy-6-iodo-α-D-glucopyranosyl-(1→4)-O-α-D-glucopyranosyl-(1→4)-D-glucopyranose were prepared, taking advantage of the substrate specificities of Taka-amylase A and glucoamylase, and the action of Taka-amylase A on these substrates was investigated.<br> 2. The Michaelis constant Km and the molecular activity k0 were determined at 37°C and pH 5.2 using the modified maltotrioses. The values of Km and k0 decreased upon modification of maltotriose and those of k0/Km were in agreement with the comparative initial rates for the corresponding derivatives of phenyl α-maltoside at low substrate concentrations. This result suggested that a subsite of the enzyme may have a specific interaction with halogen atoms in the substrate.<br> 3. All halogenomaltotrioses examined showed substrate inhibition at high substrate con-centrations.

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