The overall goal of this project is to determine important aspects of the role of intramolecular and intermolecular structure in biological energy conversion. The structural studies proposed here concern the determination of the cylindrically-averaged profile structures of the membrane molecular components within specific bimolecular complexes involved in energy conversion at moderate resolution (approximately 10 angstroms); the spatial relationships between these components, relative to each other and to the overall profile structure of the membrane; and the spatial relationships among the redox centers associated with these components, relative to each other within these complexes and relative to the overall profile structure of the membrane, with an accuracy of +/-l-2 Angstroms. Through a correlation of such structural parameters with the capabilities of these components and/or complexes thereof to exhibit efficient electron transport and the generation of transmembrane electrochemical potentials (and ultimately the synthesis of ATP) in reconstituted,vectorially oriented single membrane systems, we hope to gain substantial insight into the mechanism of energy coupling in biological membranes. The techniques of nonresonance and resonance x-ray diffraction, neutron diffraction, EXAFS (Extended X-ray Absorption Fine Structure) and polarized EXAFS spectroscopy and optical linear dichroism will be utilized to study the relevant membrane proteins, including photosynthetic reaction centers, cytochrome oxidase, cytochrome c and cytochrome b/c1 and various bimolecular complexes thereof in the form of vectorially oriented, single membrane systems. The reaction center-cytochrome b/c1-cytochrome c complexes exhibit an efficient light-driven cyclic series of electron transfer reactions.
