カツオ肝臓α-グルコシダーゼの二,三の性質

概要

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The α-glucosidase was extracted from the skipjack liver and purified partially by the gel filtration on a Sephadex G-100 column. The molecular weight of the enzyme estimated by the gel filtration was about 100, 000. The ARRHENIUS plots showed a downward bend at 38°. The activation energy calculated for the skipjack α-glucosidase was 6, 700 cal./mole below the transition temperature and 3, 800 above that temperature. The optimum pH of the enzyme reaction was found at about pH 4.8, and the enzyme seemed to be an acid α-glucosidase. The Michaelis constant of p-nitrophenyl-α-D-glucoside for the skipjack a-glucosidase was about 10-3M at pH 4.0, 4.3, 4.6 and 4.8, and about 6×10-5 M at pH 5.2 and 5.5. NaCI and KCI were the activators of the enzyme. Turanose, glucose, gluconolactone, and erythritol inhibited the enzyme competitively, but the Ki values of these compounds were greater than the Km value of p-nitrophenyl-α-D-glucoside for the enzyme. The enzyme was inhibited noncompetitively by the heavy metal ions, and the Ki values of Ag+ and Hg2+ were much smaller than the Km value of the substrate.
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