Asymmetric binding of the high-affinity Q(H)(center dot-) ubisemiquinone in quinol oxidase (bo(3)) from Escherichia coli studied by multifrequency electron paramagnetic resonance spectroscopy

S. Grimaldi, T. Ostermann, N. Weiden, T. Mogi, H. Miyoshi, B. Ludwig, H. Michel, T.F. Prisner, F. MacMillan

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Ubiquinone-2 (UQ-2) selectively labeled with C (I = 1/2) at either the position 1- or the 4-carbonyl carbon is incorporated into the ubiquinol oxidase bo 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 (Q) is investigated using multifrequency (9, 34, and 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. The corresponding spectra reveal dramatic differences in C 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 Q 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 Q in the enzyme and contrasted with the information available on other protein-bound semiquinone radicals.
Original languageEnglish
Pages (from-to)5632–5639
Number of pages8
Issue number19
Publication statusPublished - 24 Apr 2003

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