QH*- ubisemiquinone radical in the bo3-type ubiquinol oxidase studied by pulsed electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy.
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.
Grimaldi
S
S
Institut für Physikalische und Theoretische Chemie and Institut für Biochemie, J. W. Goethe Universität Frankfurt, D-60439 Frankfurt am Main, Germany.
MacMillan
F
F
Ostermann
T
T
Ludwig
B
B
Michel
H
H
Prisner
T
T
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*
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