Hydrolysis of low molecular weight isomaltosaccharides by a p-nitrophenyl-alpha-D-glucopyranoside-hydrolyzing alpha-glucosidase from a thermophile, Bacillus thermoglucosidius KP 1006.

A p-nitrophenyl-alpha-D-glucopyranoside-hydrolyzing alpha-glucosidase of a thermophile, Bacillus thermoglucosidius KP 1006, was purified to an electrophoretically-homogeneous state. Its molecular weight was estimated as 60 000 by gel electrophoresis. The molecular activity (ko) and the Km value at 60 degrees C and pH 6.8 for p-nitrophenyl-alpha-D-glucopyranoside were 233 s-1 and 0.24 mM, respectively. The enzyme cleft the non-reducing terminal alpha-1,6-glucosidic bonds of isomaltose, panose, isomaltotriose, isomaltotetraose, and isomaltopentaose. The ko values were 72.4, 194, 208, 233 and 167 s-1, and the Km values were 3.3, 9.5, 11, 13 and 21 mM, respectively. Each isomaltosaccharide was hydrolyzed to glucose by the cleavage of single glucose units from its nonreducing end. The present study suggests that the enzyme is an oligo-1,6-glucosidase (dextrin 6-alpha-glucanohydrolase, EC 3.2.1.10) and an exo-glucosidase.