Effect of metal ions on the degradation and adsorption of two cellobiohydrolases on microcrystalline cellulose

To test the metal ion effect, hydrolysis experiments for two cellobiohydrolases (CBH I and CBH II) from Trichoderma reesei have been carried out in the presence of 10 mM metal ions, such as Cu++, Mn++, Ca++, Hg++, Ba++, Ph++, and Cd++. The addition of Mn++, Ba++, and Ca++ (10 mM) during the hydrolysis of Avicel PH 101 caused an increase in the total reducing sugar (TRS) for CBH I by 142, 135, and 114 percent, respectively. Those for CBH II increased by 177, 175, and 115 percent, respectively. The Mn++ was the most stimulatory metal ion, whereas Hg++ was the most inhibitory metal ion. The adsorption experiments were performed to investigate how the influence of Mn++ and Hg++ on the hydrolysis is related to the adsorption of cellobiohydrolases on cellulose. The increase in TRS during hydrolysis by adding Mn++ caused an increase in adsorption affinity (K-ad) and tightness (DeltaH(a)). While, the decrease of TRS during hydrolysis by adding Hg++ caused a decrease in the adsorption affinity (K-ad) and tightness (DeltaH(a)). These results indicate the changes in the tightness and affinity of adsorption by adding metal ions play a crucial role in the degradation of the microcrystalline cellulose.