Purification and characterization of an α-glucosidase from germinating millet seeds

An of-glucosidase (alpha-(D)-glucoside glucohydrolase, EC 3.2.1.20) was isolated from germinating millet (Panicum miliaceum L.) seeds by a procedure that included ammonium sulfate fractionation, chromatography on CM-cellulofine/Fractogel EMD SO3, Sephacryl S-200 HR and TSK gel Phenyl-5 PW, and preparative isoelectric focusing. The enzyme was homogenous by SDS-PAGE. Tile molecular weight of the enzyme was estimated to be 86,000 based oil its mobility in SDS-PAGE and 80,000 based on gel filtration with TSKgel super SW 3000, which showed that it was composed of a single unit. The isoelectric point of the enzyme was 8.3. Tile enzyme readily hydrolyzed rnaitose, malto-oligosaccharides, and alpha-1,4-glucan, but hydrolyzed polysaccharides more rapidly than maltose. The K. value decreased with an increase in the molecular weight of the substrate. The value for maltoheptaose was about 4-fold lower than that for maltose. The enzyme preferably hydrolyzed amylopectin in starch, but also readily hydrolyzed nigerose, which has an alpha-1,3-glucosidic linkage and exists as an abnormal linkage in the structure of starch. In particular, the enzyme readily hydrolyzed millet starch from germinating seeds that had been degraded to some extent. (c) 2005 Elsevier Ltd. All rights reserved.