title: Energy-dependent Complex I-associated ubisemiquinones in submitochondrial particles.
abstract: Two distinct species of Complex I-associated ubisemiquinones (SQNf and SQNs) were detected by cryogenic EPR analysis of tightly coupled submitochondrial particles oxidizing NADH or succinate under steady-state conditions. The g = 2.00 signals from both fast-relaxing SQNf (P1/2 = 170 mW at 40 K) and slow-relaxing SQNs (P1/2 = 0.7 mW) are sensitive to uncouplers, rotenone and thermally induced deactivation of Complex I. At higher temperatures the SQNf signal is broadened and only the SQNs signal is seen (P1/2 = 7 mW at 105 K). The spin-spin interaction between SQNf and the iron-sulfur cluster N2 was detected as split peaks of the g parallel 2.5 signal with a coupling constant of 1.65 mT, revealing their mutual distance of 8-11 A. The data obtained are consistent with a model in which N2 and two interacting bound ubisemiquinone species are spatially arranged within the hydrophobic domain of Complex I, participating in the vectorial proton translocation.
authors.affiliation: Department of Biochemistry, School of Biology, Moscow State University, Russian Federation.
authors.forename: A D
authors.initials: AD
authors.lastname: Vinogradov
authors.forename: V D
authors.initials: VD
authors.lastname: Sled
authors.forename: D S
authors.initials: DS
authors.lastname: Burbaev
authors.forename: V G
authors.initials: VG
authors.lastname: Grivennikova
authors.forename: I A
authors.initials: IA
authors.lastname: Moroz
authors.forename: T
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D000818:Animals; D002417:Cattle; D003067:Coenzymes; D004578:Electron Spin Resonance Spectroscopy; D006358:Hot Temperature; D007506:Iron-Sulfur Proteins / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000302:isolation & purification* / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012402:Rotenone / Q000494:pharmacology; D013367:Submitochondrial Particles / Q000201:enzymology*; D013816:Thermodynamics; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D003067:Coenzymes; D007506:Iron-Sulfur Proteins; D012402:Rotenone; D014451:Ubiquinone; D016660:NAD(P)H Dehydrogenase (Quinone); C024989:coenzyme Q10