Purification and characterization of an endoglucanase from a newly isolated thermophilic anaerobic bacterium

An endoglucanase (1,4-beta-D-glucan glucanohydrolase, EC 3.2.1.4) from a new cellulolytic thermophilic bacterium was purified to apparent homogeneity after being separated from a xylanase. Little carbohydrate was associated with the endoglucanase. A molecular weight of 91,000 and 99,000 was determined by SDS-polyacrylamide gel electrophoresis and by gel filtration of the native enzyme on Ultrogel ACA 34. The optimal pH was approximately 6.4 and the enzyme was isoelectric at pH 3.85. The enzyme was found highly thermostable: it retained 50 per cent of its activity after 1 hour at 85 degrees C. Hydrolysis of CMC took place with a rapid decrease in viscosity but a slow liberation of reducing sugars, indicating endo-enzyme activity. It showed little capacity to hydrolyze highly ordered cellulose. Cellobiose inhibited the activity of the endoglucanase. None of the metal ions tested stimulated the activity. The enzyme was completely inactivated by 1 mM Hg2+ and was inhibited by thiol reagents.