Two forms of α-glucosidase from sugar-beet seeds

Two forms of α-glucosidase (EC 3.2.1.20), designated as I and II, have been isolated from sugarbeet (Beta vulgaris L.) seeds by a procedure including fractionation with ammonium sulfate and ethanol, carboxymethyl-cellulose column chromatography, and preparative disc gel electrophoresis. The two enzymes were homogeneous by polyacrylamide disc gel electrophoresis. Their molecular weights were 98,000 (I) and 60,000 (II). α-Glucosidase I readily hydrolyzed maltose, isomaltose, kojibiose, maltotriose, panose, amylose, soluble starch, amylopectin and glycogen. α-Glucosidase II also hydrolyzed maltose, kojibiose and maltotriose but hydrolyzed the other substrates only very weakly or not at all. α-Glucosidase I hydrolyzed soluble starch at a faster rate than maltose. It produced isomaltose and panose as the main α-glucosyltransfer products from maltose, whereas maltotriose was the main product of α-glucosidase II. α-Glucosidase I hydrolyzed amylose liberating α-glucose. The neutral-sugar content was calculated to be 2.7% for α-glucosidase I and 8.8% for α-glucosidase II. The main neutral sugar was mannose in α-glucosidase I, and glucose in α-glucosidase II.