Abstract
Enzymatic hydrolysis of cellulosic biomass is a complex process involving many factors, including multiple enzymes, heterogeneous substrates, and multi-step enzyme reactions. Cellulase researchers have conventionally used a double-exponential equation to fit the experimental time course of product formation, but no theoretical basis for this has been established. Here we present a mechanism-based equation that fits well the progress curves of cellulase reaction, incorporating the concepts of non-productive and productive binding on the cellulose surface and processivity. The derived equation is double exponential. Our findings indicate that the reaction mechanism of cellulase itself can account for the double-exponential nature of the progress curve independently of other factors that may contribute, such as substrate heterogeneity and involvement of other enzymes.