Hydrolysis of steam-pretreated lignocellulose - Synergism and adsorption for cellobiohydrolase I and endoglucanase II of Trichoderma reesei

The mechanism of hydrolysis of cellulose is important for improving the enz ymatic conversion in bioprocesses based on lignocellulose, Adsorption and h ydrolysis experiments were performed with cellobiohydrolase I (CBH I) and e ndoglucanase II (EG II) from Trichoderma reesei on a realistic lignocellulo se substrates.. steam-pretreated willow. The enzymes were studied both alon e and in equimolar mixtures. Adsorption isotherms were determined at 4 and 40 degrees C during 90-min reaction times. Both CBH I and EG II adsorbed st ronger at 40 than at 4 degrees C. The time course of adsorption and hydroly sis, 3 min to 48 h, was studied at 40 degrees C. About 90% of the cellulase s were adsorbed within 2 h. The hydrolysis rate was high in the beginning b ut decreased during the time course. Based on adsorption data, the hydrolys is and synergism were analyzed as function of adsorbed enzyme. CBH I showed a linear correlation between hydrolysis and adsorbed enzyme, whereas for E G II the corresponding curve leveled off at both 4 and 40 degrees C. At low conversion, below 1%, EG II produced as much soluble sugars as CBH I. At h igher conversion, CBH I was more efficient than EG II. The synergism as fun ction of adsorbed enzyme increased with bound enzyme before reaching a stab le value of about 2. The effect of varying the ratio of CBH I:EG II was stu died at fixed total enzyme loading and by changing the ratio between the en zymes. 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 CB H I was not critical. The ratio 40% EG II:60% CBH I showed similar conversi on to 5% EG II:95% CBH I. Modifications of the conventional endo-exo synerg ism model are proposed.