Purification and characterization of cellulolytic enzymes produced byAspergillus nidulans

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Abstract
Three exo-glucanases, two endo-glucanases and two .beta.-glucosidases were separated and purified from the culture medium of Aspergillus nidulans. The optimal assay conditions for all forms of cellulase components ranged from pH 5.0 to 6.0 and 50.degree. C and 65.degree. C for exo-glucanases and endo-glucanases but 35.degree. C and 65.degree. C for .beta.-glucosidases. A close relation of enzyme stability to their optimal pH range was observed. All the cellulase components were stable for 10 min at 40-50.degree. C. Exo-II and Exo-III (Km, 38.46 and 37.71 mg/ml) had greater affinity for the substrate than Exo-I (Km, 50.00 mg/ml). The Km values of Endo-I and Endo-II (5.0 and 4.0 mg/ml) and their maximum reaction velocities Vmax, 12.0 and 10.0 IU/mg protein) were comparable. .beta.-glucosidases exhibited Km values of 0.24 and 0.12 mmol and Vmax values of 8.00 and 0.67 IU/mg protein. The molecular weights recorded for various enzyme forms were: Exo-I, 29,000; Exo-II, 72,500; Exo-III, 138,000; Endo-I, 25,000; Endo-II, 32,500; .beta.-Gluco-I, 14,000 and .beta.-Gluco-II, 26,000. Exo- and endoglucanases were found to require some metal ions as co-factors for their catalytic activities whereas .beta.-glucosidases did not. Hg2+ inhibited the activity of all the cellulase components. The saccharification studies demonstrated a high degree of synergism among all the three cellulase components for hydrolysis of dewaxed cotton.