PURIFICATION AND CHARACTERIZATION OF CELLULOLYTIC ENZYMES PRODUCED BY ASPERGILLUS-NIDULANS

Three exo‐glucanases, two endo‐glucanases and two β‐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°C and 65°C for exo‐glucanases and endo‐glucanases but 35°C and 65°C for β‐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°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. β‐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, 29000; Exo‐II, 72500; Exo‐III, 138000; Endo‐I, 25000; Endo‐II, 32500; β‐Gluco‐I, 14000 and β‐Gluco‐II, 26000. Exo‐ and endo‐glucanases were found to require some metal ions as co‐factors for their catalytic activities whereas β‐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. Copyright © 1990, Wiley Blackwell. All rights reserved