Ionic strength dismutase reactions

Another illustration of the power of molecular dynamics simulation can be drawn from the sphere of enzyme catalysis. Many enzyme-catalyzed reactions proceed at a rate that depends on the diffusion-limited association of the substrate with the active site. Sharp et al. [28] have carried out Brownian dynamics simulations of the association of superoxide anions with superoxide dismutase (SOD). The active center in SOD is a positively charged copper atom. The distribution of charge over the enzyme is not uniform, and so an electric field is produced. Using their model, Sharp et al. [28] have shown that the electric field enhances the association of the substrate with the enzyme by a factor of 30 or more. Their calculations also predict correctly the response of the association rate to changes in ionic strength and amino... 

In aprotic media, (O2) behaves like a strong nucleophile but in protic media, it is only weakly nucleophilic, due to the presence of protons. Thus, reactions of (02) in protic media are determined by kinetic rather than by thermodynamic parameters (concentrations, pH, ionic strength). The most important reaction in terms of biological effects is the dismutation of (02) (Eqs. (4) and (5)), which proceeds rather slowly in physiological conditions (ATdis-S X 10 M s at pH 7.4 Halliwell and Gutteridge, 1989), but can be considerably favoured by superoxide dismutases (SOD) (EC 1.15.1.1) (Chance et al., 1979 1.6 x 10 M-> s" ). 

BELLONI - You mentioned the examples of the superoxyde anion dismutation catalyzed by the superoxyde dismutase and of the aggregation of colloids which are both multisteps processes. I wonder how, without sufficient knowledge of the slowest reaction governing the mechanism, the ionic strength effects found can be explained by your predictions ... 

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