Hydrolysis ofα-1,4- andα-l,6-Glucosidic Linkages in Trisaccharides by theThermoactinomyces vulgarisα-Amylase

The action of Thermoactinomyces vulgarisα-amylase was examined in order to elucidate whether this α-amylase catalyzes the hydrolysis of α-1, 4- and α-l, 6-glucosidic linkages in some oligosaccharides at the same catalytic site. The optimum pH for its action on maltotriose and isopanose (α-d-Glcp-(l→4)-α-d-Glcp-(1→6)-d-Glcp) was 4.5, which was the same as the value for starch and pullulan. Hydrolysis patterns of isopanose by this α-amylase were dependent on the substrate concentration. At a low substrate concentration (0.5%) equimolar maltose and glucose were produced from isopanose. At a high substrate concentration (4.0%) a small amount of isomaltose was found besides maltose and glucose, while the molar ratio of glucose to maltose plus isomaltose was unity at the early reaction stages. Hydrolysis patterns of reducing end-(14C)-labeled maltotriose was also dependent on substrate concentration. Increasing the substrate concentration from 0.5 to 4.0%, the molar ratio of labeled glucose to labeled maltose in the products was decreased from 6 to 1.5. Apparent formation of labeled glucose was depressed by the addition of isopanose to the labeled maltotriose-hydrolyzing mixture. The results above supported the view that this enzyme can hydrolyze α-l, 6-glucosidic linkage as well as α-l, 4-glucosidic linkage in isopanose or maltotriose at the same site.