Kinetics of Hydrolytic Reaction Catalyzed by Crystalline Bacterial α-Amylase. II. The Influence of Solvent

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The influence of methanol on the rate of the hydrolytic reaction of soluble starch catalyzed by crystalline bacterial amyloclastic α-amylase has been studied at 25°C and pH 6.0, over the methanol concentration of 0∼22.6% by weight. The apparent Michaelis constant, Km, is independent of the methanol concentration, while the breakdown rate constant of the ES complex, k3, decreases with an increase in the methanol concentration. The plot of logk3 versus the reciprocal dielectric constant of the solvent gives a straight line with a negative slope. Various possible effects on the reaction rates caused by the addition of methanol have been examind, and it has been concluded that the dielectric constant effect is predominantly operative. The results have been interpreted quantitatively on the basis of the electrostatic theory previously developed by one of the present authors. The results of calculation have been found to be consistent with the hypothesis that charge separation occurs in the glucosidic linkage to be hydrolyzed in the activated state of the ES complex. The electrostatic entropy of activation in the breakdown of the ES complex has also been estimated.
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