title: EPR detection of two protein-associated ubiquinone components (SQ(Nf) and SQ(Ns)) in the membrane in situ and in proteoliposomes of isolated bovine heart complex I.
abstract: The success of Sazanov's group in determining the X-ray structure of the whole bacterial complex I is a great contribution to the progress of complex I research. In this mini-review of 35years' history of my laboratory and collaborators, we characterized the function of protein-associated semiquinone molecules in the proton-pumping mechanism in complex I (NADH-quinone oxidoreductase). We have constructed most of the frame work of our hypothesis, utilizing EPR techniques before the X-ray structures of complex I were reported by Sazanov's and Brandt's groups. One of the semiquinones (SQ(Nf)) is extremely sensitive to a proton motive force imposed on the energy-transducing membrane, while the other (SQ(Ns)) is insensitive. Their sensitivity to rotenone inhibition also differs. These differences were exploited using tightly coupled bovine heart submitochondrial particles with a high respiratory control ratio (>8). We determined the distance between SQ(Nf) and iron-sulfur cluster N2 on the basis of their direct spin-spin interaction. We are extending this line of work using reconstituted bovine heart complex I proteoliposomes which shows a respiratory control ratio >5. Two frontier research groups support our view point based on their mutagenesis studies. High frequency (33.9GHz; Q-band) EPR experiments appear to favor our two-semiquinone model. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA. Ohnishi@mail.med.upenn.edu
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ohnishi
authors.forename: S Tsuyoshi
authors.initials: ST
authors.lastname: Ohnishi
authors.forename: Kyoko
authors.initials: K
authors.lastname: Shinzawa-Itoh
authors.forename: Shinya
authors.initials: S
authors.lastname: Yoshikawa
authors.forename: Ralph T
authors.initials: RT
authors.lastname: Weber
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D042967:Electron Transport Complex I / Q000737:chemistry / Q000378:metabolism; D008929:Mitochondria, Heart / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009124:Muscle Proteins / Q000737:chemistry* / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D018892:Proton-Motive Force / Q000502:physiology
chemical_list: D016227:Benzoquinones; D024101:Mitochondrial Proteins; D009124:Muscle Proteins; C025232:semiquinone radicals; D042967:Electron Transport Complex I