Microcrystalline cellulose (10 mg of Avicel/ml) was hydrolysed to glucose by different concentrations of the purified cellulase components endoglucanase (EG) II and cellobiohydrolases (CBH) I and II, alone and in combination with each other, in the presence of excess beta-glucosidase. At a concentration of 360 micrograms/ml (160 micrograms of EG II/ml, 100 micrograms of CBH I/ml and 100 micrograms of CBH II/ml) the degree of synergism among them was negligible. As the concentration of cellulase decreased, the degree of synergism increased, reaching an optimum at 20 micrograms/ml (5 micrograms of EG II/ml, 10 micrograms of CBH I/ml and 5 micrograms of CBH II/ml). There was no apparent relationship between the ratio of the components and the degree of synergism. The latter is probably due, though it could not be proved, to the level of saturation of the substrate with each component. Inhibition of Avicel hydrolysis was observed when the substrate was incubated with saturating and nonsaturating concentrations of a mixture of EG II and CBH I respectively. A similar result was also observed with a combination of EG I and EG II.

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