Mechanisms of Electron Transfer in Cytochromes and Blue Copper Proteins

The mechanisms of electron transfer in cytochromes and bluecopper proteins are investigated by examining the oxidation and reduction of horse heart cytochrome c, Pseudomonas aeruginosa cytochrome c551, Rhus vernicifera stellacyanin, Phaseolus vulgaris plastocyanin and Pseudomonas aeruginosa azurin by inorganic redox agents. The rates of electron transfer in these systems have been analyzed within the framework of the relative Marcus theory of outer sphere electron transfer. The activation parameters for these processes have also been examined. The reduction of Pseudomonas aeruginosa cytochrome c551, by Fe(EDTA)2- has been investigated. The electrostatics-corrected self-exchange rate constant is similar to that obtained for horse heart cytochrome c. The close correspondence indicates that the two proteins employ similar electron transfer mechanisms. It is proposed that this mechanism. involves reagent contact and little protein conformational change at the partially exposed heme edge.