Multiple Forms of α-Glucosidase from Pig Duodenum

Abstract

Multiple forms of neutral α-glucosidase (pH optima, 6.0-6.5) were purified from pig duodenal mucosa by a procedure including Triton X-100 treatment, fractionation with ammonium sulfate, fractionation with ethyl alcohol, DEAE-cellulose column chromatography and preparative polyacrylamide disc gel electrophoresis. All of the α-glucosidases, I_a, II_a, I_b and II_b, were found to be homogeneous on polyacrylamide disc gel electrophoresis. The molecular weights, isoelectric points and optimum temperatures of α-glucosidases I_a and II_a were 145, 000-150, 000, pH 3.5-3.7 and 55°C, respectively, and both enzymes were stable up to 55-16 on treatment at pH 6.0 for 15min; whereas those of the other two α-glucosidases, I_b and II_b, were 80, 000, pH 4.0 - 4.1 and 65°C, respectively, and both enzymes were stable up to 70°C on the same treatment. The Km values of enzyme II_a for maltose, maltotriose and amylose were 1.72mM, 0.37mM and 1.67mg/ml, while those of enzyme II_b were 3.33 mM, 2.61 mM and 11.8mg/ml, respectively. All enzyme hydrolyzed α-, 1-4- α-1, 3- and α-1, 2-glucosidic linkages in substrates, but showed no activity on sucrose or isomaltose. Enzymes II_a and II_b hydrolyzed phenyl α-maltoside to glucose and phenyl α-glucoside, and maltotriose was formed as the main α-glucosyltransfer product from maltose. It was revealed that two types of neutral α-glucosidases having no activity toward sucrose or isomaltose existed in pig duodenal mucosa, and that one type comprised α-glucosidase having both maltose- and amylaceous α-glucan-hydrolyzing activities and the other type heat-stable maltooligosaccharidases which hydrolyzed amylaceous α-glucan weakly.