Evolution of enzyme activity: Is diffusion control important? Activation parameters in the reactions of ferric heme species with hydrogen peroxide

Abstract

There is a finite energy of activation for a diffusion-controlled reaction. It can be calculated by comparing a combination of the Stokes-Einstein relation between the diffusion coefficient of a solute molecule and the viscosity of a solvent and the Smoluchowski equation for a diffusion-controlled rate constant to the rate equation of simple transition state theory. The entropy of activation for a diffusion-controlled reaction can also be obtained. Comparison is made of the enthalpy and entropy of activation for a diffusion-controlled reaction to the enthalpies and entropies of reaction of a series of heme-containing proteins and a simple heme with hydrogen peroxide