Kinetics of Hydrolytic Reaction Catalyzed by Crystalline Bacterial α-Amylase. I. The Influence of pH

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  • Ono Sôzaburo
    Laboratory of Biophysical Chemistry College of Agriculture University of Osaka Prefecture
  • Hiromi Keitaro
    Laboratory of Biophysical Chemistry College of Agriculture University of Osaka Prefecture
  • Yoshikawa Yoshiko
    Laboratory of Biophysical Chemistry College of Agriculture University of Osaka Prefecture

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The influence of pH on the rate of the hydrolytic reactions of amylose catalyzed by the crystalline bacterial α-amylase of Bac. amyloliquefaciens Fukumoto has been examined at various substrate concentrations and temperatures.<BR>The apparent Michaelis constant \={K}m is constant over the pH range examined (3.6∼8.4), whereas the apparent rate constant k2 for the breakdown of the enzymesubstrate complex into the reaction products and free enzyme decreases on both the acid and the alkaline side of the optimum pH 5.85. The relative rate - pH curves are not affected by the substrate concentration. From these facts, it is concluded that at least two ionizable groups in the enzyme are involved in the breakdown of the complex, although these groups are not directly responsible for the formation of the enzyme-substrate complex.<BR>The ionization constants and the heats of ionization of the two groups involved in the reaction have been determined. From these values, the ionizing groups are inferred to be the carboxyl and imidazole (or amino) groups. The ionized form of the former and the positively charged form of the latter are considered to be essential for the breakdown process.<BR>Tentative mechanisms of the reaction are proposed.

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