Hydrolysis of steam-pretreated lignocellulose
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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.
Index EntriesTrichoderma reesei cellulase cellulose hydrolysis lignocellulose cellobiohydrolase endoglucanase synergism adsorption
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- 2.Teeri, T. T. and Koivula, A. (1995), Carbohydr. Europe 12, 28–33.Google Scholar
- 8.Kleman-Leyer, K. M., Siika-aho, M., Teeri, T. T., and Kirk, T. K. (1996), Appl. Environ. Microbiol. 62, 2883–2887.Google Scholar
- 18.Ståhlberg, J., Johansson, G., and Pettersson, G. (1993), Biochim. Biophys. Acta 1157, 107–113.Google Scholar
- 21.Medve, J. (1997), PhD thesis, Lund University, Lund, Sweden.Google Scholar
- 25.Nidetzky, B., Steiner, W., and Claeyssens, M. (1994), Biochem. J. 303, 817–823.Google Scholar
- 27.Woodward, J., Lima, M., and Lee, N. E. (1988), Biochem. J. 255, 895–899.Google Scholar
- 28.Nidetzky, B., Steiner, W., Hayn, M., and Claeyssens, M. (1994), Biochem. J. 298, 705–710.Google Scholar