PURIFICATION AND CHARACTERIZATION OF ENDOGLUCANASE-SS FROM CLOSTRIDIUM-THERMOCELLUM

The extracellular cellulolytic enzymes of the thermophilic anaerobe Clostridium thermocellum occur as a protein complex or aggregate known as the cellulosome. By using a combination of ion-exchange, adsorption and hydrophobic-interaction chromatography, it was possible to isolate from extracellular broth a specific endoglucanase of interest without the use of denaturants. The endoglucanase was identified as the cellulosomal subunit S(S) by the use of specific antibodies. The enzyme has an M(r) of 83 000, an isoelectric point of 3.55, optimum pH of 6.6 and optimum temperature of 70-degrees-C. It hydrolyses CM-cellulose and, at a higher rate, the cellodextrins, cellotetraose and cellopentaose, but does not hydrolyse a crystalline cellulose such as Avicel. Cellobiose and cellotriose are also immune to attack. It differs from endoglucanases previously isolated by others and a 76 000-M(r) endoglucanase recently isolated in this laboratory.