Oxidoreduction properties of bound ubiquinone in Complex I from Escherichia coli.
The exploration of the redox chemistry of bound ubiquinone during catalysis is a prerequisite for the understanding of the mechanism by which Complex I (nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase) transduces redox energy into an electrochemical proton gradient. Studies of redox dependent changes in the spectrum of Complex I from Escherichia coli in the mid- and near-ultraviolet (UV) and visible areas were performed to identify the spectral contribution, and to determine the redox properties, of the tightly bound ubiquinone. A very low midpoint redox potential (<-300mV) was found for the bound ubiquinone, more than 400mV lower than when dissolved in a phospholipid membrane. This thermodynamic property of bound ubiquinone has important implications for the mechanism by which Complex I catalyzes proton translocation.
Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, PO Box 65 (Viikinkaari 1), FIN-00014 Helsinki, Finland. Electronic address: Marina.Verkhovskaya@Helsinki.Fi.
Marina
M
Verkhovskaya
Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, PO Box 65 (Viikinkaari 1), FIN-00014 Helsinki, Finland.
Mårten
M
Wikström
D000693:Anaerobiosis; D042967:Electron Transport Complex I / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet; D014451:Ubiquinone / Q000378:metabolism*
D009243:NAD; D014451:Ubiquinone; D042967:Electron Transport Complex I
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; Bound ubiquinone; Complex I; E(h); E(m); E(m,7); GDH; HEPES; LDH; Mid UV-range; Redox spectrum; SHE; ambient redox potential relative to SHE; glucose dehydrogenase; lactate dehydrogenase; midpoint redox potential at pH=7, relative to SHE; midpoint redox potential relative to SHE; standard hydrogen electrode; time constant; τ