Free-energy dependence of electron transfer in cytochrome c labeled with ruthenium(II)-polypyridine complexes

by Wright, J. L.; Wang, K.; Geren, L.; Saunders, A. J.; Pielak, G. J.; Durham, B.; Millett, F.

The free-energy dependence of the rate constants for intramol. electron transfer in yeast cytochrome c covalently bound to a series of ruthenium(II)-polypyridine complexes has been determined The H39C;C102T variant of yeast cytochrome c was attached to a series of ruthenium complexes through a thioether linkage involving the sulfur atom of Cys39 and a methylene carbon of 4,4'-dimethylbipyridine. The free energies of reaction cover a range from 0.75 to 1.26 V with intramol. rate constants of 4-9×105 s-1. The observed rate constants are consistent with reactions in which the free energies of reaction are nearly equal to the reorganization energy. In the present case, the reorganization energy for electron transfer between the ruthenium complex and the heme iron is 1 eV.