Properties of exoglucanase from Aspergillus niger.

Abstract

Exoglucanase (EC 3.2.1.91) was partially purified from Aspergillus niger. The enzyme was stable at room temperature in the pH range of 4.0-6.0 for 24h, with the optimum at 5.5. The enzyme had an optimum temperature of 50°C and a t112 at 65°C was 70 min. Km and Vmax values were found to be 55.5 mg/ml and 0.9 ,uM/min, respectively. Glycerol protected the enzyme from inactivation on storage and from denaturation due to freezing and thawing. The effect of the sulfhydryl group reagents tested suggested the presence of -SH on the active site of the enzyme. Mn2+ and Co2+ were good activators of the enzyme, whereas Hg2 + and Pb2 + were potent inhibitors. The enzyme was a metalloprotein, or it requires certain metal ions for activation.

Effect of adding cofactors to exogenous fibrolytic enzymes on preingestive hydrolysis, in vitro digestibility, and fermentation of bermudagrass haylage

“…Adding Mn 2+ to 2A, 11A, and 13D resulted in 1.05-, 1.38-, and 1.13-fold increases in release of WSC. This agrees with studies showing that adding Mn 2+ increased the activity of exoglucanases (Singh et al, 1990), endoglucanases (Saad and Fawzi, 2004), β-glucosidase (Riou et al, 1998), and β-xylosidase (John and Schmidt, 1988). That Mn 2+ increased the activity of several fibrolytic enzymes explains why its greatest effects were on 11C and 2A, which had among the greatest total cellulolytic activities and lowest manganese-to-protein ratios (0.004 and 0.003 vs. 0.005 mg of manganese/g of protein), respectively.…”

“…Adding Co 2+ also increased release of WSC by all EFE except 1A. This agrees with previous work that indicated adding Co 2+ increased exoglucanase (Singh et al, 1990) and endoglucanase activities (Saad and Fawzi, 2004), which determine the rate of cellulose digestion (Zhang and Lynd, 2004). The synergistic increase in release of WSC due to adding Co 2+ to EFE was greatest for 11C, probably because it had one of the lowest cobalt-to-protein ratios (0.0003 vs. 0.0006 mg of cobalt/g of protein).…”

“…Effects of adding metal ion cofactors (COF), to exogenous fibrolytic enzymes (EFE) on preingestive hydrolysis of a 4-wk regrowth of bermudagrass haylage (experiment 1) COF addition to EFE on release of WSC of forage cell walls, though others have investigated effects of COF addition to fibrolytic enzymes on hydrolysis of pure substrates (Tejirian and Xu, 2010) or steam-pretreated biofuel biomass (Bin and Hongzhang, 2010). Singh et al (1990) reported that activity of exoglucanase II (E.C. 3.2.1.91, which acts on the nonreducing end of cellulose) from Aspergillus niger was increased 1.82-, 1.51-, 1.40-, and 1.85-fold when undisclosed doses of Mn 2+ , Ca 2+ , Mg 2+ , or Co 2+ were added, respectively.…”

“…These results may indicate that cellulolytic activities were stimulated by adding Mn 2+ but xylanolytic activities were not. Manganese increases the activity of exoglucanases, endoglucanases, and β-glucosidases (Singh et al, 1990;Riou et al, 1998;Saad and Fawzi, 2004), which are all involved in cellulose depolymerization. In an early study by Chamberlain and Burroughs (1962), omission of manganese from an in vitro ruminal fluid medium reduced cellulose digestibility.…”

Polyploid Formation Between Aspergillus niger and Trichoderma viride For Enhanced Citric Acid Production From Cellulose

“…Exoglucanases release glucose from cellulose and glucooligosaccharides. The difference between exoglucanases and cellobiohydrolases is not always clear because of differences in the methods used to study these enzymes [11][12][13][14][15][16][17]. Enzymatic hydrolysis of cellulose is of major importance in both natural and engineered systems in which utilization of cellulosic biomass occurs.…”