Studies on the Substrate Specificity of Taka-Amylase A1

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Abstract
1. O-6-Deoxy-αD-glucopyranosyl-(l→4)-O-α-D-glucopyranosyl-(l→4)-D-glucopyranose, 0-6-chloro-6-deoxyαD-glucopyranosyl-(l→4)-Oα-D-glucopyranosyl-(l→4)-O-D-glucopyranose, 0-6-brom-O-6-deoxy-α-D-glucopyranosyl-(l→4)Oα-D-glucopyranosyl-(l→4)-D-glucopyranose, and O-6-deoxy-6-iodo-O-α-D-glucopyranosyl-(l→4)Oα-D-glucopyranosyl-(l→4)-D-glucopyra-nose 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. 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 ko 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. 3. All halogenomaltotrioses examined showed substrate inhibition at high substrate concentrations.

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