QH.- ubisemiquinone radical in the bo3-type ubiquinol oxidase studied by pulsed electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy

Stéphane Grimaldi, Fraser Macmillan, Thomas Ostermann, Bernd Ludwig, Hartmut Michel, Thomas Prisner

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The high-affinity Q(H) ubiquinone-binding site in the bo(3) ubiquinol oxidase from Escherichia coli has been characterized by an investigation of the native ubiquinone radical anion Q(H)(.-) 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 Q(H)(.-) with a nitrogen nucleus from the surrounding protein matrix. From analysis of the experimental data, the N-14 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 tu a protein backbone nitrogen. This result is discussed with regard to the location and potential function of Q(H) in the enzyme.
Original languageEnglish
Pages (from-to)1037-1043
Number of pages7
Issue number4
Publication statusPublished - 2001

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