Investigation of the Mechanism of Proton Translocation by Nadh:ubiquinone Oxidoreductase (Complex I) from Bovine Heart Mitochondria: Does the Enzyme Operate by a Q-cycle Mechanism?
From: Medical Research Council Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 2XY, UK.
The Biochemical journal
- Publish Date: Dec 2006
- ISSN: 1470-8728
- Volume: 400
- Issue: 3
- Pages: 541-50
- Medium: Internet
- Language: English
- Citation (JAMA): Sherwood Steven, Hirst Judy, et al. Investigation of the Mechanism of Proton Translocation by Nadh:ubiquinone Oxidoreductase (Complex I) from Bovine Heart Mitochondria: Does the Enzyme Operate by a Q-cycle Mechanism?. Biochem. J. Dec 2006;400:541-50
Abstract
Complex I (NADH:ubiquinone oxidoreductase) is the first enzyme of the membrane-bound electron transport chain in mitochondria. It conserves energy, from the reduction of ubiquinone by NADH, as a protonmotive force across the inner membrane, but the mechanism of energy transduction is not known. The structure of the hydrophilic arm of thermophilic complex I supports the idea that proton translocation is driven at (or close to) the point of quinone reduction, rather than at the point of NADH oxidation, with a chain of iron-sulfur clusters transferring electrons between the two active sites. Here, we describe experiments to determine whether complex I, isolated from bovine heart mitochondria, operates via a Q-cycle mechanism analogous to that observed in the cytochrome bc1 complex. No evidence for the ‘reductant-induced oxidation’ of ubiquinol could be detected; therefore no support for a Q-cycle mechanism was obtained. Unexpectedly, in the presence of NADH, complex I inhibited by either rotenone or piericidin A was found to catalyse the exchange of redox states between different quinone and quinol species, providing a possible route for future investigations into the mechanism of energy transduction.
Mesh Headings (Keywords): Animals, Cattle, Electron Transport Complex I, Energy Metabolism, Mitochondria, Heart, Models, Biological, Protons, Quinones, Ubiquinone
Check for Full Text / PubMed Unique Identifier (PMID): 16895522
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