抄録
The action of Thermoactinomyces vulgaris α-amylase was examined in order to elucidate whether this α-amylase catalyzes the hydrolysis of α-1, 4-and α-1, 6-glucosidic linkages in some oligosaccharides at one catalytic site. Polyacrylamide gel electrophoresis of this amylase showed that the activities on starch and isopanose migrated exactly the same position as the enzyme protein band. The optimum pH for its action on maltotriose and isopanose was 4.5, while was almost the same as the values for starch and pullulan. Action patterns on isopanose were dependent on the substrate concentration. At low substrate concentration (0.5%) equimolar maltose and glucose were produced from isopanose. At high substrate concentration (4.0%) small amount of isomaltose was found besides maltose and glucose, equimolar glucose and sum of maltose and isomaltose were pro-duced at the early reaction stages. Action patterns on 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-1, 6-glucosidic linkages as well as α-1, 4-glucosidic linkages in isopanose or maltotriose at the same catalytic site. Moreover the action of this enzyme on IP6 (a-D-Glcp-(1→4)-α-D-Glcp-(1→6)-α-D-Glcp- (1→4) -α-D-Glcp- (1→4) -α-D-Glcp- (1→6) -D-Glcp), TV6 (α-D-Glcp- (1→6) -α-D-Glcp- (1→4) -α-D-Glcp- (1→4) -α-D-Glcp- (1→6) -α-D-Glcp- (1→4) -D-Glcp) and P6 (α-D-Glcp- (1→4) -α-D-Glcp- (1→4) -α-D-Glcp-(1→6)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-D-Glcp)was examined by using paper chromatography. Other four kinds of α-amylases tested cleaved isopanose to produce glucose, maltose and isomaltose; especially Bacillus subtilis saccharifying a-amylase and Taka amylase A produced larger amounts of isomaltose than others.
