Extending the Michaelis-Menten kinetic scheme, we consider a three-state diffusion-controlled reaction model to investigate the effects of fluctuating reaction rate on the blinking statistics of single-enzyme catalytic reactions. As a result of conformational changes, the barrier-height and the reaction rate for the bottleneck enzymatic reaction could fluctuate in time, leading to non-exponential blinking statistics. To illustrate model applications, some reported experimental data for single beta-galactosidase molecules were reanalyzed here to extract useful kinetic parameters. (c) 2008 Elsevier B. V. All rights reserved.