THE RESPIRATORY SUBSTRATE RHODOQUINOL INDUCES Q-CYCLE BYPASS REACTIONS IN THE YEAST CYTOCHROME bc1 COMPLEX - MECHANISTIC AND PHYSIOLOGICAL IMPLICATIONS
Journal Article
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· Journal of Biological Chemistry
The mitochondrial cytochrome bc1 complex catalyzes the transfer of electrons from ubiquinol to cyt c, while generating a proton motive force for ATP synthesis, via the ''Qcycle'' mechanism. Under certain conditions, electron flow through the Q-cycle is blocked at the level of a reactive intermediate in the quinol oxidase site of the enzyme, resulting in ''bypass reactions'', some of which lead to superoxide production. Using analogs of the respiratory substrates, ubiquinol-3 and rhodoquinol-3, we show that the relative rates of Q-cycle bypass reactions in the Saccharomyces cerevisiae cyt bc1 complex are highly dependent, by a factor of up to one hundred-fold, on the properties of the substrate quinol. Our results suggest that the rate of Q-cycle bypass reactions is dependent on the steady state concentration of reactive intermediates produced at the quinol oxidase site of the enzyme. We conclude that normal operation of the Q-cycle requires a fairly narrow window of redox potentials, with respect to the quinol substrate, to allow normal turnover of the complex while preventing potentially damaging bypass reactions.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 876945
- Report Number(s):
- PNWD-SA-7040; 13297; 2358a; 2358
- Journal Information:
- Journal of Biological Chemistry, Journal Name: Journal of Biological Chemistry Journal Issue: 41 Vol. 280; ISSN 0021-9258; ISSN JBCHA3
- Country of Publication:
- United States
- Language:
- English
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