(447c) On the Reactivity of Cellulose in Enzymatic Hydrolysis

The slow down in enzymatic hydrolysis of cellulose with conversion has often been attributed to declining reactivity of the substrate as the more easily reacted material is thought to be consumed preferentially. To better understand the cause of this phenomenon, the enzymatic reaction of Avicel cellulose was interrupted over the course of nearly complete hydrolysis. Our initial results showed that the rate of cellulose hydrolysis, expressed as the percentage of remaining substrate at the testing time, was approximately constant over a wide range of conversions for restart experiments but declined continually with conversion for uninterrupted hydrolysis. Furthermore, the cellulose hydrolysis rate per adsorbed enzyme was approximately constant for the restart procedure but declined with conversion when enzymes were left to react. Thus, the drop off in reaction rate for uninterrupted cellulose digestion by enzymes could not be attributed to changes in substrate reactivity, suggesting that other effects such as enzymes getting ?stuck? or otherwise slowing down may be responsible. A theory of enzymatic hydrolysis of cellulose to describe this behavior will be presented.