Proton Pumping of Mitochondrial Complex I: Differential Activation by Analogs of Ubiquinone |
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Authors: | Leon Helfenbaum Anna Ngo Anna Ghelli Anthony W Linnane Mauro Degli Esposti |
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Affiliation: | (1) Centre for Molecular Biology and Medicine, Monash University, Clayton, 3168 Victoria, Australia;(2) Department of Biology, University of Bologna, Bologna, Italy;(3) Present address: Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, 3052, Victoria, Australia |
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Abstract: | As part of the ongoing studies aimed at elucidating the mechanism of the energy conserving function of mitochondrial complex I, NADH: ubiquinone (Q) reductase, we have investigated how short-chain Q analogs activate the proton pumping function of this complex. Using a pH-sensitive fluorescent dye we have monitored both the extent and initial velocity of proton pumping of complex I in submitochondrial particles. The results are consistent with two sites of interaction of Q analogs with complex I, each having different proton pumping capacity. One is the physiological site which leads to a rapid proton pumping and a stoichiometric consumption of NADH associated with the reduction of the most hydrophobic Q analogs. Of these, heptyl-Q appears to be the most efficient substrate in the assay of proton pumping. Q analogs with a short-chain of less than six carbons interact with a second site which drives a slow proton pumping activity associated with NADH oxidation that is overstoichiometric to the reduced quinone acceptor. This activity is also nonphysiological, since hydrophilic Q analogs show little or no respiratory control ratio of their NADH:Q reductase activity, contrary to hydrophobic Q analogs. |
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Keywords: | NADH: ubiquinone reductase ubiquinone proton pumping mitochondria |
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