alpha-Glucosidase, a membrane-bound enzyme of alpha-glucan metabolism in Bacillus amyloliquefaciens. Purification and partial characterization.

The organism Bacillus amyloliquefaciens is capable of producing alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) and isoamylase (glycogen 6-glucanohydrolase, EC 3.2.1.68) extracellurlarly and a membrane-bound, intracellular alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20). The amounts of alpha-glucosidase in cells of B. amyloliquefaciens grown on amylaceous polysaccharides were significantly higher then in cells grown on non-carbohydrate carbon sources. alpha-Glucosidase was exclusively found associated with membranes from ruptured spheroplasts by subcellular fractionation and solubilization studies. Salt solutions and chelating agents alone did not dislodge alpha-glucosidase from membranes, but in combination with detergents were most effective in solubilizing active enzyme (0.1% sodium cholate (pH 8.0)/0.4 M sodium chloride). Purified alpha-glucosidase very rapidly hydrolized p-nitrophenyl alpha-D-glucopyranoside and sucrose. Maltose, maltotriose, isomaltose and isomaltotriose were hydrolized at slower rates, whereas beta-glucosides and polymeric alpha-glucans were not attacked. Other properties of the purified enzyme were as follows: Temperature optimum for catalysis = 39 +/- 1 degrees C; pH optimum = 6.8; molecular weight = 27,000 +/- 1000. alpha-Glucosidase is proposed to function in the endogenous metabolism of alpha-glucans provided extracellularly as carbon sources for growth of B. amyloliquefaciens.