Tuesday, April 20, 2010
8-25

Inhibition of cellulose hydrolysis by xylooligomers of different chain length: Data and kinetics

Qing Qing and Charles E. Wyman. University of California, Center for Environmental Research and Technology, 1084 Columbia Avenue, Riverside, CA 92507

The high cost of cellulase impedes commercialization of cellulosic ethanol production, and the slowdown in enzymatic hydrolysis of lignocellulosic biomass with conversion results in low yields for low enzyme loadings.  Inhibition by glucose and cellobiose, loss of enzyme activity, drop in substrate reactivity, and nonproductive binding of enzyme to lignin are among the factors that could account for this loss of effectiveness.  However, our recent results suggest that xylooligomers that are released from pretreated biomass during enzymatic hydrolysis are stronger inhibitors than established for glucose and cellobiose.  Furthermore, mixed xylooligomers containing a range of chain lengths dramatically decreased enzymatic conversion rates and yields of both pure cellulose and pretreated biomass. To clarify the relative importance of different xylooligomers, Gel Permeation Chromatography (GPC) was applied to separate xylooligomers according to their chain length, and selected fractions were added to hydrolysis of pure cellulose to determine their relative influence on hydrolysis rates.  Furthermore, comparisons were made to inhibition by glucan derivatives. Kinetic models were then developed based on this data to characterize the inhibition constants of the different xylooligomers and clarify their relative importance in slowing conversion rates.

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