Kinetic modeling of cellulose hydrolysis with first order inactivation of adsorbed cellulase.

Enzymatic hydrolysis involves complex interaction between enzyme, substrate, and the reaction environment, and the complete mechanism is still unknown. Further, glucose release slows significantly as the reaction proceeds. A model based on Langmuir binding kinetics that incorporates inactivation of adsorbed cellulase was developed that predicts product formation within 10% of experimental results for two substrates. A key premise of the model, with experimental validation, suggests that V(max) decreases as a function of time due to loss of total available enzyme as adsorbed cellulases become inactivated. Rate constants for product formation and enzyme inactivation were comparable to values reported elsewhere. A value of k(2)/K(m) that is several orders of magnitude lower than the rate constant for the diffusion-controlled encounter of enzyme and substrate, along with similar parameter values between substrates, implies a common but undefined rate-limiting step associated with loss of enzyme activity likely exists in the pathway of cellulose hydrolysis.