title: Proton pumping of mitochondrial complex I: differential activation by analogs of ubiquinone.
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.
authors.affiliation: Centre for Molecular Biology and Medicine, Monash University, Clayton, Victoria, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Helfenbaum
authors.forename: A
authors.initials: A
authors.lastname: Ngo
authors.forename: A
authors.initials: A
authors.lastname: Ghelli
authors.forename: A W
authors.initials: AW
authors.lastname: Linnane
authors.forename: M
authors.initials: M
authors.lastname: Degli Esposti
mesh_terms: D000609:Aminoacridines / Q000737:chemistry; D004789:Enzyme Activation; D005456:Fluorescent Dyes / Q000737:chemistry; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000187:drug effects / Q000378:metabolism*; D017494:Proton Pumps / Q000187:drug effects*; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000609:Aminoacridines; D005456:Fluorescent Dyes; D017494:Proton Pumps; D014451:Ubiquinone; C010847:9-amino-6-chloro-2-methoxyacridine; D016660:NAD(P)H Dehydrogenase (Quinone)