HYDROLYSIS OF LOW-MOLECULAR WEIGHT ISOMALTOSACCHARIDES BY A PARA-NITROPHENYL-ALPHA-D-GLUCOPYRANOSIDE-HYDROLYZING ALPHA-GLUCOSIDASE FROM A THERMOPHILE, BACILLUS-THERMOGLUCOSIDIUS-KP-1006

A p-nitrophenyl-α-d-glucopyranoside-hydrolyzing α-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 (k0) and the Km value at 60°C and pH 6.8 for p-nitrophenyl-α-d-glucopyranoside were 233 s-1 and 0.24 mM, respectively. The enzyme cleft the non-reducing terminal α-1,6-glucosidic bonds of isomaltose, panose, isomaltotriose, isomaltotetraose, and isomaltopentaose. The k0 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 non-reducing end. The present study suggests that the enzyme is an oligo-1,6-glucosidase (dextrin 6-α-glucanohydrolase, EC 3.2.1.10) and an exo-glucosidase. © 1979.