Electron Transfer in Structurally Engineered Metalloproteins

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This project, supported by the Inorganic, Bioinorganic and Organometallic Program, is for continuation of studies of the factors that affect long-range electron transfer in biological systems. Genetically engineered mutants of yeast iso-1-cytochrome c, which have histidine residues substituted for the native amino acid at various sites on the periphery of the protein, will be used for these studies. Introduction of redox active, luminescent ruthenium complexes, by complexation at these histidine sites, allows for the spectroscopic monitoring of electron-transfer to, or from, the metalloenzyme over well-known, fixed distances. A recently developed laser flash-quench technique will be used to determine the electron-transfer rates. This technique has two major advantages for these studies over previous methods. First, it allows for study of the protein with the native iron, rather than a metal substituted version, and second, it permits the study of a much wider range of transfer rates. In a second phase of the research, similarly modified human myoglobins will be used for the study of the coupling of single electron transfers to multielectron events such as generation of a ferryl (Fe=O) species. The overall objective of these studies is to determine the mechanism by which the electron moves from the donor to the acceptor over distances of 10 angstroms and greater. %%% Electron transfer is one of the most important processes in biological systems. An intriguing aspects of these electron transfers is that the electron donor and acceptor are frequently separated by large distances. Whereas theories of electron transfer over short distances, where overlap of donor and acceptor orbitals can occur, is well developed, the mechanism by which the electron moves over long distances is not well understood. Studies such as these may ultimately result in better treatment of certain physiological disorders and in new methods of solar energy conversion.