Clostridium thermocellum Endoglucanase Produced in Escherichia coli

was purified from extracts of plasmid-bearing E. coli cells by heat treatment and chromatography on DEAE-Trisacryl. It was characterized as a thermophilic endo-4-1,4-glucanase, the properties of which closely resemble those of endoglucanase A previously isolated from C. thermocellum supernatants. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis the enzyme purified from E. coli exhibited two protein bands with molecular weights of 49,000 and 52,000. It had a temperature optimum at 75°C and was stable for several hours at 60°C. Endoglucanase activity was optimal between pH 5.5 and 6.5. The enzyme was insensitive against end product inhibition by glucose and celiobiose and remarkably resistant to the denaturing effects of detergents and organic solvents. It was capable of degrading, in addition to cellulosic substrates, glucans with alternating 0-1,4 and 0-1,3 linkages such as barley I8-glucan and lichenan.