Cellulose hydrolysis by a highly thermostable endo-1,4-β-glucanase (Avicelase I) from Clostridium stercorarium

Avicelase I was purified to homogeneity from culture supernatants of the cellulolytic thermophile Clostridium stercorarium and shown to be identical with a previously described endo-β-1,4-glucanase from this organism. Both Avicelase and carboxymethylcellulase (CMCase) activity were found to reside on a monomeric protein of 100 kDa. The enzyme acts on microcrystalline cellulose without requiring additional proteins or cofactors. Hydrolysis of Avicel occurs at a maximum rate at temperatures around 90°C. At 60°C the enzyme is completely stable and degrades Avicel at a constant rate for several days without loss of activity. Cellotriose and cellotetraose were identified as hydrolysis intermediates. Cellotetraose is preferentially cleaved into glucose and cellotriose, which is slowly hydrolysed to cellobiose and glucose. Due to its higher stability and catalytic efficiency, Avicelase I compares favorably with fungal enzymes considered for technical cellulose hydrolysis.