Q-Band ENDOR (Electron Nuclear Double Resonance) of the High-Affinity Ubisemiquinone Center in Cytochrome bo3 from Escherichia coli

• Published in: Biochemistry (Easton) Vol. 39; no. 11; pp. 3169 - 3175
• Main Authors: VESELOV, Andrei V., OSBORNE, Jeffrey P., GENNIS, Robert B., SCHOLES, Charles P.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.03.2000
• Subjects: Benzoquinones - chemistry; Coenzymes; Cytochromes - chemistry; Deuterium; Electron Spin Resonance Spectroscopy - methods; Escherichia coli - enzymology; Escherichia coli Proteins; Protons; Ubiquinone - analogs & derivatives; Ubiquinone - chemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi9926835

Electron nuclear double resonance (ENDOR) was performed on the protein-bound, stabilized, high-affinity ubisemiquinone radical, QH*-, of bo3 quinol oxidase to determine its electronic spin distribution and to probe its interaction with its surroundings. Until this present work, such ENDOR studies of protein-stabilized ubisemiquinone centers have only been done on photosynthetic reaction centers whose function is to reduce a ubiquinol pool. In contrast, QH*- serves to oxidize a ubiquinol pool in the course of electron transfer from the ubiquinol pool to the oxygen-consuming center of terminal bo3 oxidase. As documented by large hyperfine couplings (>10 MHz) to nonexchangeable protons on the QH*- ubisemiquinone ring, we provide evidence for an electronic distribution on QH*- that is different from that of the semiquinones of reaction centers. Since the ubisemiquinone itself is physically nearly identical in both QH*- and the bacterial photosynthetic reaction centers, this electronic difference is evidently a function of the local protein environment. Interaction of QH*- with this local protein environment was explicitly shown by exchangeable deuteron ENDOR that implied hydrogen bonding to the quinone and by weak proton hyperfine couplings to the local protein matrix.