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Journal Article

QH*- Ubisemiquinone Radical in the bo3-Type Ubiquinol Oxidase Studied by Pulsed Electron Paramagnetic Resonance and Hyperfine Sublevel Correlation Spectroscopy

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Ostermann,  Thomas
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;
Institut für Biochemie, J. W. Goethe Universität Frankfurt, 60439 Frankfurt am Main, Germany;

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Michel,  Hartmut       
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Grimaldi, S., MacMillan, F., Ostermann, T., Ludwig, B., Michel, H., & Prisner, T. (2001). QH*- Ubisemiquinone Radical in the bo3-Type Ubiquinol Oxidase Studied by Pulsed Electron Paramagnetic Resonance and Hyperfine Sublevel Correlation Spectroscopy. Biochemistry, 40(4), 1037-1043. doi:10.1021/bi001641+.


Cite as: https://hdl.handle.net/21.11116/0000-0006-F8BF-C
Abstract
The high-affinity QH ubiquinone-binding site in the bo3 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 14N nuclear quadrupolar parameters have been determined:  κ = e2qQ/4h = 0.93 MHz and η = 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.