Monday, May 4, 2009
5-20
The Effect of Xylooligomers on Enzymatic Hydrolysis of Cellulose and Pretreated Corn Stover
Qing Qing, Bin Yang, and Charles Wyman. University of California, Center for Environmental Research and Technology, 1084 Columbia Avenue, Riverside, CA 92507
High doses of expensive cellulase are required to obtain satisfactory yields from biological conversion of cellulosic biomass, and enzyme costs must be reduced if cellulosic ethanol is to become a reality. Typically, the rate of hydrolysis is fast initially but then slows down more rapidly than can be explained by just consumption of substrate. Thus, factors such as enzyme inhibition, loss of activity, a drop in substrate reactivity, or nonproductive binding of enzyme to lignin could be responsible for this loss of effectiveness. Although glucose and cellobiose are known to inhibit enzymatic hydrolysis, we recently reported that xylose, xylan, and xylooligomers also appear to dramatically decrease conversion rates and yields. In this study, addition of xylan and various xylooligomers dramatically reduced the rates and yields for Avicel hydrolysis at low enzyme loadings and had a greater effect than adding equal amounts of xylose derived from these materials or when added separately. In addition, the effectiveness of combinations of cellulase, beta-glucosidase, xylanase, and beta-xylosidase in relieving inhibition of hydrolysis for Avicel and pretreated corn stover was evaluated. Kinetic models were then developed based on this data to characterize the inhibition constants of the different inhibitors and clarify their relative importance in slowing conversion rates.