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Journal Article

Asymmetric binding of the high-affinity QH.- ubisemiquinone in quinol oxidase (bo3) from Escherichia coli studied by multifrequency electron paramagnetic resonance 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, 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., Ostermann, T., Weiden, N., Mogi, T., Miyoshi, H., Ludwig, B., et al. (2003). Asymmetric binding of the high-affinity QH.- ubisemiquinone in quinol oxidase (bo3) from Escherichia coli studied by multifrequency electron paramagnetic resonance spectroscopy. Biochemistry, 42(19), 5632-5639. doi:10.1021/bi034010z.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0024-DB61-9
Abstract
Ubiquinone-2 (UQ-2) selectively labeled with 13C (I =1/2) at either the position 1- or the 4-carbonyl carbon is incorporated into the ubiquinol oxidase bo3 from Escherichia coli in which the native quinone (UQ-8) has been previously removed. The resulting stabilized anion radical in the high-affinity quinone-binding site (QH•-) is investigated using multifrequency (9, 34, and 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. The corresponding spectra reveal dramatic differences in 13C hyperfine couplings indicating a strongly asymmetric spin density distribution over the quinone headgroup. By comparison with previous results on labeled ubisemiquinones in proteins as well as in organic solvents, it is concluded that QH•- is most probably bound to the protein via a one-sided hydrogen bond or a strongly asymmetric hydrogen-bonding network. This observation is discussed with regard to the function of QH in the enzyme and contrasted with the information available on other protein-bound semiquinone radicals.