A NOVEL TYPE OF THERMOSTABLE ALPHA-D-GLUCOSIDASE FROM THERMOANAEROBACTER-THERMOHYDROSULFURICUS EXHIBITING MALTODEXTRINOHYDROLASE ACTIVITY

An alpha-glucosidase with the ability to attack polymeric substrates w as purified to homogeneity from culture supernatants of Thermoanaeroba cter thermohydrosulfricus DSM 567. The enzyme is apparently a glycopro tein with a molecular mass of 160 kDa. Maximal activity is observed be tween pH 5 and 7 at 75 degrees C. The alpha-glucosidase is active towa rds p-nitrophenyl-alpha-D-glucoside, maltose, malto-oligosaccharides, starch and pullulan. Highest activity is displayed towards the disacch aride maltose. In addition to glucose, maltohexaose and maltoheptaose can be detected as the initial products of starch hydrolysis. After sh ort incubations of pullulan, glucose is found as the only product. At high substrate concentrations, maltose and malto-oligosaccharide, but not glucose, are used as accepters for glucosyltransfer. These finding s indicate that the T. thermohydrosulfricus enzyme represents a novel type of alpha-glucosidase exhibiting maltase, glucohydrolase and 'malt odextrinohydrolase' activity.