Hydrolysis of steam-pretreated lignocellulose: Synergism and adsorption for cellobiohydrolase I and endogulcanase II of trichoderma reesei
Source: Applied Biochemistry and Biotechnology, Volume 82, Number 3, December 1999 , pp. 243-258(16)
Publisher: Humana Press
Abstract:The mechanism of hydrolysis of cellulose is important for improving the enzymatic conversion in bioprocesses based on lignocellulose. Adsorption and hydrolysis experiments were performed with cellobiohydrolase I (CBH I) and endoglucanase II (EG II) from Trichoderma reesei on a realistic lignocellulose substrates: steam-pretreated willow. The enzymes were studied both alone and in equimolar mixtures. Adsorption isotherms were determined at 4 and 40°C during 90-min reaction times. Both CBH I and EG II adsorbed stronger at 40 than at 4°C. The time course of adsorption and hydrolysis, 3 min to 48 h, was studied at 40°C. About 90% of the cellulases were adsorbed within 2 h. The hydrolysis rate was high in the beginning but decreased during the time course. Based on adsorption data, the hydrolysis and synergism were analyzed as function of adsorbed enzyme. CBH I showed a linear correlation between hydrolysis and adsorbed enzyme, whereas for EG II the corresponding curve leveled off at both 4 and 40°C. At low conversion, below 1%, EG II produced as much soluble sugars as CBH I. At higher conversion, CBH I was more efficient than EG II. The synergism as function of adsorbed enzyme increased with bound enzyme before reaching a stable value of about 2. The effect of varying the ratio of CBH I:EG II was studied at fixed total enzyme loading and by changing the ratio between the enzymes. Only a small addition (5%) of EG II to a CBH I solution was shown to be sufficient for nearly maximal synergism. The ratio between EG II and CBH I was not critical. The ratio 40% EG II:60% CBH I showed similar conversion to 5% EG II:95% CBH I. Modifications of the conventional endo-exo synergism model are proposed.
Document Type: Research Article
Affiliations: 1: Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, PO Box 124, S-221 00, Lund, Sweden, 2: Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, PO Box 124, S-221 00, Lund, Sweden, Email: firstname.lastname@example.org
Publication date: December 1, 1999