The molecular mechanisms by which two energy-transducing enzyme systems, mitochondrial cytochrome oxidase and the photosynthetic reaction center, operate will be studied. Cytochrome oxidase maintains electron transfer activity in the mitochondrion by catalyzing the four electron reduction of dioxygen to water according to the following reaction 4cty c2+ +O2 +4H+->4 cyt c3+ +2H2O It is also the locus of site III respiratory control and contributes directly to the transmembrane proton gradient by pumping protons stoichiometrically with electrons transported. By using a variety of spectroscopic techniques, including EPR and static and time-resolved resonance Raman spectroscopies, we intend to test various models for the proton pumping mechanism, including one that we developed earlier. We will use the same assortment of techniques to continue our efforts to measure vibrational spectra for partially metabolized intermediates in dioxygen and hydrogen peroxide reduction and to assess conformation restrictions imposed by the enzyme active site. Oxidases from both plant and animal sources will be used in these studies. In photosynthetic reaction centers, photon absorption produces a series of electron transfer reactions that lead to a charge separated state in the sub-ns time regime. This process provides an excellent system by which to study fast electron transfer reactions and we intend to employ ps time-resolved optical and Raman techniques to characterize electronic and vibrational changes that accompany the charge separation. Model compound studies of neutral porphyrin and chlorin species, of their pi-pi* excited states, and of their one-electron oxidized cation radicals will be carried out in order to facilitate data interpretation for the biological systems. Our initial work will be done with photosynthetic bacterial reaction centers and will proceed to Photosystem II reaction center from oxygen-evolving higher plant species.
Showing the most recent 10 out of 50 publications
