Purification and Substrate Specificity of Brewer’s Yeast α-Glucosidase

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Abstract
Three kinds of α-glucosidase (I, II and III) were isolated from brewer’s yeast, α-Glucosidases I and II were homogeneous in disc electrophoresis, but α-glucosidase III was not. Their pH-optima were found to be in the range of 6.3 to 7.1. Each of them was a typical α-glucosidase showing a preferential activity on phenyl-α-glucoside. α-Glucosidase I was so-called isomaltase which could hydrolyze isomaltose but not maltose. α-Glucosidases II and III showed no activity on isomaltose. The ratio of velocity of hydrolysis for phenyl-α-glucoside (Km, 2.9 mm) and isomaltose (Km, 28.6 mm) of α-glucosidase I was calculated to be 100:9 in that order, and those for phenyl-α-glucoside (Km’s, 0.8 mm and 3.6 mm) and maltose (Km’s, 14.3 mm and 71.4 mm) of α-glucosidases II and III were calculated to be 100: 17 and 100: 18, respectively.