Intramolecular electron transfer between Ru(I) and Ru(III) and the heme iron of cytochrome c labeled with ruthenium(II) polypyridine complexes

Abstract

The rates of intramolecular electron transfer between Ru(III) and Fe(II) of three derivatives of cytochrome c labeled at lysines 86, 8 and 7 with Ru(4,4′-dicarboxybipyridine)(bipyridine) 2 2+ have been measured. The respective rate constants are 1.1×10 5, 1.3×10 5 and 6×10 5 s −1. Corresponding rates of electron transfer between Ru(I) and Fe(III) of these derivatives have also been measured. The respective rate constants are 3.3×10 5, 5.7×10 5 and 1×10 6 s −1. In addition the rate constant for a derivative labeled at lysine 87 was determined to be 2.7×10 5 s −1. The two sets of rate constants appeared to be correlated with each other with respect to the location of the ruthenium label. The Ru(I) rate constants are 2–3 times larger than the corresponding Ru(III) rate constants. Preliminary analysis suggests that the observed rate constants are not consistent with the large free energy of reaction expected for Ru(I).