Long-range electron transfer in ruthenium-modified cytochrome c: evaluation of porphyrin-ruthenium electronic couplings in the Candida krusei and horse heart proteins

Abstract

Experiments in several laboratories have shown that electron transfer (ET) can take place at appreciable rates over long distances (> 10 {angstrom}) in organic and inorganic molecules and in proteins. There is a bewildering array of potential ET pathways in proteins; interestingly, the through-peptide routes (if there are any) generally involve so many bonds that they cannot possibly account for the observed rates. In searching for good pathways through cytochrome c, the authors discovered a relatively short route from His-39 to the heme in the Candida krusei (C.k.) protein. Along this route, the crucial shortcut is a hydrogen bond that bridges Gly-41 and the heme. Since experimental information relevant to protein pathway models is lacking, they have extracted donor-acceptor electronic coupling constants from an analysis of the driving-force dependence of ET rates in Ru(His-39)-modified C.k. zinc cytochrome c.