A cell-bound β-glucosidase (β-d-glucoside glucohydrolase; EC 3.2.1.21) from Clostridium thermocellum was purified to apparent homogeneity. A molecular weight of about 43000 gel fluration of the native enzyme on Ultrogel AcA34. A constant ratio of aryl-β-glucosidase and cellcouse throughout purification, similar heat stabilities, pH profiles and sensitivity to different hiibitor and competitive inhibition of the aryl-β-gluosidase and the β suggest that the same enzyme accounts for the aryl-β-glucosidase and the cellobiase activities. However, the affinity for cellobiose was very much lower than for p-β-d-glucoside. The β-glucosidase had maximum rates at pH 6·0 to 6·5 for both activities. The enzyme was specific for substrates with the both activities. β-configuration. particulary and β-1,3 and β-1,2 linkages. The enzyme did not hydrolyse carboxymethylcellulose or cellulose, but hydrolysed cello-oligosaccharides. It was strongly inhibited by d-glucono-δ-lactone was sensitive to thiol reagents. When preparations of C. thermocellm cellulase were supplemented with purified β-glucosidase, glucose was the predominant product of cellulose and the rate of saccharification was increased.

Summary: The cellulolytic system from culture filtrates of Clostridium thermocellum, when partially purified by preparative electrophoresis, showed a single protein band on analytical polyacrylamide gel electrophoresis; however, sodium dodecyl sulphate-polyacrylamide gel electrophoresis indicated that at least five proteins were present. Carbohydrate was present in the purified fraction and it is suggested that the cellulase was present as a complex.

A β-glucosidase was isolated from Clostridium thermocellum; the enzyme was localized in the periplasmic space.