The Mechanism of Enzymatic Cellulose Degradation

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Abstract
A cellulolytic enzyme (“C1” enzyme) has been isolated from a commercial cellulase preparation derived from culture filtrates of the fungus Trichoderma viride. The purification method is a four‐step procedure including chromatography on Bio‐Gel P‐10, DEAE‐Sephadex chromatography, isoelectric focusing and chromatography on Bio‐Gel P‐60. A yield of 144 mg enzyme was obtained per 100 g commercial cellulase. The isolated enzyme was homogeneous in polyacrylamide gel electrophoresis at pH 5.0 and at pH 8.0 by isoelectric focusing in a polyacrylamide gel and also in the ultracentrifuge. No enzyme activity towards carboxymethylcellulose could be detected in the purified material under the assay conditions used. Similarly, there was no β‐glucosidase activity. The purified enzyme was associated with 3.3% carbohydrate and is assumed to be a glycoprotein. The enzyme was isoelectric at pH 3.79 (10°C). A molecular weight of 46000 was determined by chromatography of the reduced and alkylated enzyme on a calibrated column of Sepharose 6B in 6 M guanidine‐HCl. Crystalline cellulose (Avicel), phosphoric acid‐swollen Avicel and cellotetraose were degraded by the enzyme and in each case the principle reaction product was cellobiose. Evidence indicates that the purified enzyme is a β‐1,4‐glucan cellobiohydrolase.

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