The effect of enzyme and substrate levels on the specific hydrolysis rate of pretreated poplar wood

Abstract

The hydrolysis of pretreated poplar wood was carried out with initial concentrations of 1.26, 2.52, 5.04 mg proteinJmL of GC123Trichoderma reesei. cellulase and substrate concentrations of 2.5% wJv, 5% w/v, and 10% wJv at pH 4.8 and 40°C. The concentration of enzyme protein remaining in solution, the glucose concentration, and the total potential glucose concentrations were measured as a function of time during the hydrolysis. The enzyme rapidly adsorbed initially, reaching a maximum in about 30 min. About 55–75% of the cellulase returned to solution as the remaining cellulose was hydrolyzed. Dilution of the unhydrolyzed residue, largely lignin, did not cause additional desorption of the cellulase. The specific hydrolysis rate (i.e., the rateJamount of adsorbed enzyme) declined significantly with increased conversion, even when corrected for glucose inhibition. At a given initial substrate concentration, the specific rate was found to be largely independent of the total enzyme concentration. However, at a given fractional conversion, the specific rate was found to be reduced by increased substrate concentration.