Metalloprotein Electron Transfer Mechanisms

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In this project supported by the Inorganic, Bioinorganic and Organometallic Chemistry Program, Harry B. Gray of the California Institute of Technology will investigate the factors that control long-range electron transfer in biological systems. The studies will lead to a better understanding of the biochemical oxidation-reduction mechanisms in life processes. The dependence of the rate of electron transfer on donor- acceptor separation and reaction driving force (Gibbs free energy) will be studied in several derivatives of sperm whale myoglobin and horse heart cytochrome c. A methodology will be developed to modify surface histidines with tetraammine- ruthenium pyridinium complexes which will allow introduction of organic acceptor moieties in four well-defined positions on the surface of myoglobin. Semisynthetic procedures will be used to place organic acceptors at position-82 inside cytochrome c (phenylalanine-82 will be replaced by fluoro- and cyano-phenyl- alanines). Combined driving force/distance-variation electron transfer experiments will be carried out on the modified myoglobins. Photoinduced charge separation and charge recombination reactions in zinc porphyrin/position-82-acceptor cytochrome c derivatives will be investigated.