APPARENT SUBSTRATE-INHIBITION OF THE TRICHODERMA-REESEI CELLULASE SYSTEM

The apparent substrate inhibition properties of the cellulase enzyme system from Trichoderma reesei have been characterized. Rates of saccharification were measured by quantification of solubilized reducing sugars released from an insoluble, microcrystalline, cellulose substrate. The enzyme system does not obey classical saturation kinetics. Increasing substrate concentrations corresponded to increasing rates of solubilization of reducing sugar equivalents up to an optimum, above which the rate appeared to decrease asymptotically. Graded increases in the reaction mixture enzyme concentration caused approximately proportional increases in the apparent optimum substrate concentration. The maximum inhibition observed was approximately 70% relative to that rate observed at the optimum substrate concentration. A cellobiohydrolase, CBHI, representing approximately 25% of the total enzyme mass was purified and found to obey saturation kinetics under equivalent assay conditions. Addition of CBHI to the complete enzyme system resulted in corresponding increases in the rate of saccharification without noticeably affecting the optimum substrate concentration for the reaction mixture.