title: Q-band ENDOR (electron nuclear double resonance) of the high-affinity ubisemiquinone center in cytochrome bo3 from Escherichia coli.
abstract: Electron nuclear double resonance (ENDOR) was performed on the protein-bound, stabilized, high-affinity ubisemiquinone radical, QH*-, of bo3 quinol oxidase to determine its electronic spin distribution and to probe its interaction with its surroundings. Until this present work, such ENDOR studies of protein-stabilized ubisemiquinone centers have only been done on photosynthetic reaction centers whose function is to reduce a ubiquinol pool. In contrast, QH*- serves to oxidize a ubiquinol pool in the course of electron transfer from the ubiquinol pool to the oxygen-consuming center of terminal bo3 oxidase. As documented by large hyperfine couplings (>10 MHz) to nonexchangeable protons on the QH*- ubisemiquinone ring, we provide evidence for an electronic distribution on QH*- that is different from that of the semiquinones of reaction centers. Since the ubisemiquinone itself is physically nearly identical in both QH*- and the bacterial photosynthetic reaction centers, this electronic difference is evidently a function of the local protein environment. Interaction of QH*- with this local protein environment was explicitly shown by exchangeable deuteron ENDOR that implied hydrogen bonding to the quinone and by weak proton hyperfine couplings to the local protein matrix.
authors.affiliation: Department of Chemistry, University at Albany, SUNY, Albany, New York 12222, USA.
authors.forename: A V
authors.initials: AV
authors.lastname: Veselov
authors.forename: J P
authors.initials: JP
authors.lastname: Osborne
authors.forename: R B
authors.initials: RB
authors.lastname: Gennis
authors.forename: C P
authors.initials: CP
authors.lastname: Scholes
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D003067:Coenzymes; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry*; D003903:Deuterium; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D011522:Protons; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D016227:Benzoquinones; D003067:Coenzymes; D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; D011522:Protons; C083850:cytochrome bo3, E coli; D014451:Ubiquinone; C025232:semiquinone radicals; D003903:Deuterium; C024989:coenzyme Q10