TAILIEUCHUNG - Báo cáo khoa học: Cellulose crystallinity – a key predictor of the enzymatic hydrolysis rate

The enzymatic hydrolysis of cellulose encounters various limitations that are both substrate- and enzyme-related. Although the crystallinity of pure cellulosic Avicel plays a major role in determining the rate of hydrolysis by cellulases from Trichoderma reesei, we show that it stays constant during enzymatic conversion. The mode of action of cellulases was investigated by studying their kinetics on cellulose samples. | ỊFEBS Journal Cellulose crystallinity - a key predictor of the enzymatic hydrolysis rate Melanie Hall Prabuddha Bansal Jay H. Lee Matthew J. Realff and Andreas S. Bommarius Schoolof Chemicaland Biomolecular Engineering Georgia Institute of Technology Atlanta GA USA Keywords Cel7A cellulases cellulose crystallinity hydrolysis Trichoderma reesei Correspondence A. Bommarius Schoolof Chemicaland Biomolecular Engineering Georgia Institute of Technology 311 Ferst Drive Atlanta GA 30332-0100 USA Fax 1 404 894 2291 Tel 1 404 385 1334 E-mail Received 13 December 2009 revised 16 January 2010 accepted 18 January 2010 doi The enzymatic hydrolysis of cellulose encounters various limitations that are both substrate- and enzyme-related. Although the crystallinity of pure cellulosic Avicel plays a major role in determining the rate of hydrolysis by cellulases from Trichoderma reesei we show that it stays constant during enzymatic conversion. The mode of action of cellulases was investigated by studying their kinetics on cellulose samples. A convenient method for reaching intermediate degrees of crystallinity with Avicel was therefore developed and the initial rate of the cellulase-catalyzed hydrolysis of cellulose was demonstrated to be linearly proportional to the crystallinity index of Avicel. Despite correlation with the adsorption capacity of cellulases onto cellulose at a given enzyme loading the initial enzymatic rate continued to increase with a decreasing crystallinity index even though the bound enzyme concentration stayed constant. This finding supports the determinant role of crystallinity rather than adsorption on the enzymatic rate. Thus the cellulase activity and initial rate data obtained from various samples may provide valuable information about the details of the mechanistic action of cellulase and the hydrolysable reactive fractions of cellulose chains. X-ray diffraction provides insight into the

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