title: QH*- ubisemiquinone radical in the bo3-type ubiquinol oxidase studied by pulsed electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy.
abstract: The high-affinity QH ubiquinone-binding site in the bo(3) ubiquinol oxidase from Escherichia coli has been characterized by an investigation of the native ubiquinone radical anion QH(*-) by pulsed electron paramagnetic resonance (EPR) spectroscopy. One- and two-dimensional electron spin-echo envelope modulation (ESEEM) spectra reveal strong interactions of the unpaired electron of QH(*-) with a nitrogen nucleus from the surrounding protein matrix. From analysis of the experimental data, the (14)N nuclear quadrupolar parameters have been determined: kappa = e(2)qQ/4h = 0.93 MHz and eta = 0.50. This assignment is confirmed by hyperfine sublevel correlation (HYSCORE) spectroscopy. On the basis of a comparison of these data with those obtained previously for other membrane-protein bound semiquinone radicals and model systems, this nucleus is assigned to a protein backbone nitrogen. This result is discussed with regard to the location and potential function of QH in the enzyme.
authors.affiliation: Institut für Physikalische und Theoretische Chemie and Institut für Biochemie, J. W. Goethe Universität Frankfurt, D-60439 Frankfurt am Main, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Grimaldi
authors.forename: F
authors.initials: F
authors.lastname: MacMillan
authors.forename: T
authors.initials: T
authors.lastname: Ostermann
authors.forename: B
authors.initials: B
authors.lastname: Ludwig
authors.forename: H
authors.initials: H
authors.lastname: Michel
authors.forename: T
authors.initials: T
authors.lastname: Prisner
mesh_terms: D000838:Anions; D003067:Coenzymes; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D005609:Free Radicals / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000737:chemistry*
chemical_list: D000838:Anions; D003067:Coenzymes; D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; D005609:Free Radicals; C083850:cytochrome bo3, E coli; D014451:Ubiquinone; C038862:cytochrome o oxidase; D003576:Electron Transport Complex IV; C024989:coenzyme Q10