This grant provides the remaining three years of funding for a Presidential Young Investigator Award. The research project is in the general area of bioinorganic chemistry and is concerned with the active site structures of metalloenzymes and with the factors which determine the rates of electron transfer between metalloproteins. To probe the effects of distance on rates of electron transfer, general reactions will be developed for the carbodiimide-assisted attachment of redox active transition metal complexes to lysine, glutamate, or aspartate residues of cytochrome c. This approach will generate a number of singly-modified derivatives with varying distances between the heme and the attached complex, so that measurement of intramolecular electron transfer rates will yield the distance dependence of that rate. This approach will be extended to other proteins such as myoglobin and other cytochromes. Another subproject will involve spectroscopic characterization of the Ni-containing prosthetic group of S-methyl coenzyme-M reductase, the enzyme which catalyzes the production of methane in the energy-producing cycle of methanogenic bacteria. The nature of the axial ligands bound to Ni in the enzyme will be determined using magnetic susceptibility, NMR, resonance Raman spectroscopy and x-ray absorption spectroscopy.
