This study will explore the oxygen binding site in cytochrome c oxidase and related respiratory proteins by X-ray absorption spectroscopy. Three specific objectives will be: 1) to refine the mathematical analysis of EXAFS spectra of iron porphyrins: 2) to apply the refined method of analysis to study chemically defined states of cytochrome c oxidase; and 3) to extend these results to characterize reactive intermediates in the reduction of dioxygen to water by the enzyme. X-ray absorption near edge spectroscopy and extended X-ray absorption fine structure spectroscopy will be directed initially toward the iron and copper binding centers for dioxygen in cytochrome c oxidase and toward related simpler iron and copper respiratory proteins. The work will focus on a small number of metal centers with detailed analyses of data obtained at high resolution and high signal/noise. Such high quality X-ray spectroscopic data will permit the evaluation of the mathematical models that have been used previously and extend them to include curved wave functions and multiple scattering effects. This is essential in order to relate chemical information to structural perturbations.
