Purification and Some Properties of Two α-Glucosidases in Glutinous Rice Seed

Two α-glucosidases were highly purified from glutinous rice seed by fractionation with am monium sulfate, CM-Sepharose CL-6B ion-exchange column chromatography, gel filtration, and preparative disc electrophoresis. The molecular weights were estimated to be 9.3×104 for α-glucosidase I and 8.6×104 for α-glucosidase II by SDS disc electrophoresis. The pH optima were 4.5 for α-glucosidase I and 4.3 for α-glucosidase II, and the pH stabilities of both enzymes were in the range of pH 3.5-10. α-Glucosidase I and α-glucosidase II were stable up to 40 and 50°C, respectively. The both α-glucosidases attacked not only maltose but also soluble starch. The Km values for maltose were 4.8 mM for α-glucosidase I and 2.0 mM for α-glucosidase II, and those for soluble starch were 1.7 mM for α-glucosidase I and 1.1 mM for α-glucosidase II, in the concentration of non-reducing terminal glucose. The ratios of the V values of hydrolyses of maltose to those of soluble starch were 100 : 118 for α-glucosidase I and 100 : 148 for α-glucosidase II.