Improved Method for Purification of Buckwheat α-Glucosidase and Some Kinetic Properties

Abstract

An α-glucosidase which was homogeneous in disc electrophoretic and ultracentrifugal analysis was obtained from buckwheat seeds by fractionation with ammonium sulfate, chromatography on CM-cellulose and gel filtration on Bio-Gel P-150. The sedimentation coefficient (s_{20, w}) was estimated to be 6.2 S, and the molecular weight, 80,000~88,000. The ratio of initial velocity of hydrolysis for maltose (Km = 2.13 mg/ml) and soluble starch (Km = 7.46 mg/ml) was calculated to be 100:86. Both activities were competitively inhibited by Tris and erythritol, and stimulated approximately 1.5-fold in the presence of 25 mm-K⁺ or Na⁺. The Ki values for Tris on hydrolysis of maltose and soluble starch were 0.78 mm and 1.07 mm, and those for erythritol, 77.7 mm and 64 mm, respectively.