THE INITIAL KINETICS OF HYDROLYSIS BY CELLOBIOHYDROLASE-I AND CELLOBIOHYDROLASE-II IS CONSISTENT WITH A CELLULOSE SURFACE - EROSION MODEL

Introduction of a novel method for the quantification of the cellobios e released made it possible to follow the initial stage of hydrolysis of bacterial microcrystalline cellulose (BMCC) by cellobiohydrolases 1 ,4-beta-D-glucan-cellobiohydrolase I (CBH I) and 1,4-beta-D-glucan-cel lobiohydrolase II (CBH II) from Trichoderma reesei. A drastic retardat ion of the rate of the hydrolysis was observed already at a very low d egree of conversion. Earlier-suggested retardation factors, such as pr oduct inhibition by cellobiose or enzyme inactivation, could be discou nted as primary causes for the pattern. A model including steric hindr ance by non-productive binding and erosion of the cellulose surface du ring the processive action of exoenzymes was proposed to describe the rate retardation observed. Simultaneous action of CBH I and CBH II on cellulose was not a prerequisite for synergy between them.