A diffusion Michaelis-Menten mechanism: continuous conformational change in enzymatic kinetics.

We present a simple model which extends the Michaelis-Menten mechanism by incorporating a continuous protein conformational change in enzymatic catalysis. This model can represent a quantitative version for "rack" or "induced fit" mechanisms. In the steady-state it leads to an equation of the Michaelis-Menten form, but with the catalytic step at the active site showing strong dependence on solvent viscosity. We suggest that a careful examination of solvent viscosity effects on enzymatic activity may serve as a test for the conformational change hypothesis.