Monday, April 19, 2010 - 4:00 PM
2-06

Cellulose hydrolysis kinetics is closely related to its crystalline structure

Shishir Chundawat1, Albert Cheh2, Leonardo Sousa1, Nirmal Uppugundla1, Dahai Gao1, Paul Langan3, S. Gnanakaran4, Giovanni Bellesia4, Umesh Agarwal5, Chris Bianchetti6, George Phillips Jr.6, Venkatesh Balan1, and Bruce Dale1. (1) Chemical Engineering and Materials Science, Michigan State University, Great Lakes Bioenergy Research Center (GLBRC), 3900 Collins Rd, Lansing, MI 48910, (2) Environmental Science and Chemistry, American University, Washington, DC 20016, (3) Biosciences Division, Los Alamos National Laboratory, M888 Bioscience Division Los Alamos National Lab, Los Alamos, NM 87545, (4) Theoretical Biology and Biophysics Division, Los Alamos National Laboratory, Los Alamos, NM 87545, (5) USDA-Forest Products Laboratory, Madison, WI, (6) Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706

Cellulose is known to exist in various polymorphic states (I, II, III) that vary in susceptibility to enzymatic hydrolysis. The effect of cellulose crystal structure on cellulase digestibility was explored using various cellulosic substrates (e.g. Avicel, linters, cotton, and corn stover). Native cellulose I was transformed to cellulose IIII and III by treatment with anhydrous liquid ammonia and sodium hydroxide, respectively. On the contrary, there was no formation of cellulose II or III upon treatment with ammonium hydroxide. The effect of ammonia pretreatment parameters (ammonia/water loading, residence time, temperature) on the extent of conversion of cellulose I to IIII was quantified by X-ray diffraction and Raman spectroscopy. The differential hydrolysis kinetics for cellulose depended on its crystalline form, which proceeded in the following order; Amorphous cellulose > Cellulose IIII > Cellulose II > Cellulose I. Interestingly, the enzymatic hydrolysis rate for cellulose IIII was found to be at least 2 folds greater than native cellulose I. Improvement in hydrolysis rate for cellulose III was found to be largely attributable to enhanced endoglucanase activity. Theoretical studies are being utilized to elucidate the differences in glucan chain packing (via modification of hydrogen bonding and hydrophobic interactions) for cellulose III versus native cellulose that may be responsible for the remarkable increase in the hydrolysis rate.


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