TAILIEUCHUNG - Báo cáo khoa học: A kinetic model for the burst phase of processive cellulases

Cellobiohydrolases (exocellulases) hydrolyze cellulose processively, . by sequential cleaving of soluble sugars from one end of a cellulose strand. Their activity generally shows an initial burst, followed by a pronounced slowdown, even when substrate is abundant and product accumulation is negligible. | IFEBS Journal A kinetic model for the burst phase of processive cellulases Eigil Praestgaard1 Jens Elmerdahl1 Leigh Murphy1 S0ren Nymand1 K. C. McFarland2 Kim Borch3 and Peter Westh1 1 Roskilde University NSM Research Unit for Biomaterials Roskilde Denmark 2 Novozymes Inc. Davis CA USA 3 Novozymes A S Bagsvmrd Denmark Keywords burst phase calorimetry cellulase kinetic equations slowdown of cellulolysis Correspondence P. Westh Roskilde University Building PO Box 260 1 Universitetsvej DK-4000 Roskilde Denmark Fax 45 4674 3011 Tel 45 4674 2879 E-mail pwesth@ Received 30 October 2010 revised 21 February 2011 accepted 25 February 2011 doi Cellobiohydrolases exocellulases hydrolyze cellulose processively . by sequential cleaving of soluble sugars from one end of a cellulose strand. Their activity generally shows an initial burst followed by a pronounced slowdown even when substrate is abundant and product accumulation is negligible. Here we propose an explicit kinetic model for this behavior which uses classical burst phase theory as the starting point. The model is tested against calorimetric measurements of the activity of the cellobiohy-drolase Cel7A from Trichoderma reesei on amorphous cellulose. A simple version of the model which can be solved analytically shows that the burst and slowdown can be explained by the relative rates of the sequential reactions in the hydrolysis process and the occurrence of obstacles for the pro-cessive movement along the cellulose strand. More specifically the maximum enzyme activity reflects a balance between a rapid processive movement on the one hand and a slow release of enzyme which is stalled by obstacles on the other. This model only partially accounts for the experimental data and we therefore also test a modified version that takes into account random enzyme inactivation. This approach generally accounts well for the initial time course approximately 1 h of the hydrolysis. We .

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