General Biochemical Characterization of Thermostable Extracellular beta-Amylase from Clostridium thermosulfurogenes

Abstract

Clostridium thermosulfurogenes, an anaerobic bacterium which ferments starch into ethanol at 62 degrees C, produced an active extracellular amylase and contained intracellular glucoamylase but not pullulanase activity. The extracellular amylase was purified 2.4-fold, and its general physicochemical and catalytic properties were examined. The extracellular amylase was characterized as a beta-amylase (1,4-alpha-d-glucan maltohydrolase) based on demonstration of exocleavage activity and the production of maltose with a beta-anomeric configuration from starch. The beta-amylase activity was stable and optimally active at 80 and 75 degrees C, respectively. The pH optimum for activity and the pH stability range was 5.5 to 6 and 3.5 to 6.5, respectively. The apparent [S](0.5V) and V(max) for beta-amylase activity on starch was 1 mg/ml and 60 U/mg of protein. Similar to described beta-amylase, the enzyme was inhibited by p-chloromercuribenzoate, Cu, and Hg; however, alpha- and beta-cyclodextrins were not competitive inhibitors. The beta-amylase was active and stable in the presence of air or 10% (vol/vol) ethanol. The beta-amylase and glucoamylase activities enabled the organism to actively ferment raw starch in the absence of significant pullulanase or alpha-amylase activity.