Purification and characterization of cellulolytic enzymes produced by Aspergillus nidulans

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 degrees C and 65 degrees C for exo-glucanases and endo-glucanases but 35 degrees C and 65 degrees 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 degrees 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 endo-glucanases 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.

Properties of exoglucanase from Aspergillus niger.

“…The Km and Vmax for partially purified exoglucanase, as calculated from double reciprocal plot, were found to be 55.5 mg/ml and 0.9 pM/min, respectively. The values were similar to that reported for exoglucanase from A. terreus GN-1(8), S. rolfsii (6) and A. nidulans (4).…”

Production and Characterization of Cellulolytic Enzymes by Aspergillus Niger and Rhizopus Sp. By Solid State Fermentation of Prickly Pear

“…After this time, a The optimal pH for endoglucanase and total cellulases activity was 5.0 or 6.0, similar for other Aspergillus species. The presence of endoglucanase with an optimal pH of 5.0 and 6.0 in total cellulases was reported for A. nidulans (BAGGA et al, 1990). Melanocarpus sp.…”

AspergillusEnzymes Involved in Degradation of Plant Cell Wall Polysaccharides

“…For nearly all combinations, higher faeA expression was detected in a CreA-derepressed mutant than in a wild-type strain, indicating that CreA-mediated repression occurred in the presence of all these carbon sources. Similarly, the addition of glycerol and glucose reduced the production of cellulolytic enzymes in A. nidulans (24) and A. japonicus (323), respectively. Addition of cyclic AMP relieved catabolite expression of cellulase production in glycerol-repressed A. nidulans, indicating a role for this compound in carbon catabolite repression (23).…”