Abstract
Hydrolysis of crystalline cellulose is a crucial step in utilization of cellulosic biomass and is generally the bottleneck in the biochemical process. The combination of pre-treatment and the use of suitable enzymes is the key to effective saccharification, and ammonia pretreatment is a promising technique to enhance the velocity and yield in saccharification of crystalline cellulose. In the present study, we heterologously expressed recombinant cellobiohydrolase II from Phanerochaete chrysosporium (PcCel6A) in Pichia pastoris. We then employed surface density analysis to compare the velocities of degradation of crystalline cellulose IIII, which was prepared from algal cellulose I by supercritical ammonia treatment, by the recombinant enzyme and Trichoderma reesei cellobiohydrolase I (TrCel7A). The hydrolytic velocity of crystalline cellulose IIII by PcCel6A was approximately 4 times faster than that by TrCel7A, though velocity of cellulose I degradation by PcCel6A was almost half of that by TrCel7A. Since adsorption of both enzymes on cellulose IIII is no more than twice that on cellulose I, we speculate that the enhanced hydrolysis of cellulose IIII by PcCel6A than TrCel7A is not simply due to the increased surface area, but also reflects higher accessibility of cellulose IIII to PcCel6A.
