General Biochemical Characterization of Thermostable Pullulanase and Glucoamylase from Clostridium thermohydrosulfuricum

Abstract

Cell extracts of Clostridium thermohydrosulfuricum, an anaerobic bacterium which ferments starch into ethanol at 65 degrees C, contained both pullulanase and glucoamylase activities. The general physiochemical and catalytic properties of these enzyme activities were compared. Pullulanase and glucoamylase activities were stable and optimally active at 85 and 75 degrees C, respectively. The pH optima for activity and pH stability ranges were, respectively, 5.5 to 6 and 4.5 to 5.5 for pullulanase and 4 to 6 and 5 to 6 for glucoamylase. The apparent [S](0.5v) and V(max) for pullulanase activity on pullulan were 0.33 mg/ml and 2.6 U/mg of protein. The apparent [S](0.5v) and V(max) for glucoamylase activity on starch were of 0.41 mg/ml and 0.31 U/mg of protein. These enzymes were active and stable in the presence of air or 10% (vol/vol) ethanol. These enzyme activities allowed the organism to actively degrade raw starch into glucose in the absence of significant alpha-amylase activity.