title: Electron-transfer pathways in the heme and quinone-binding domain of complex II (succinate dehydrogenase).
abstract: Single electron transfers have been examined in complex II (succinate:ubiquinone oxidoreductase) by the method of pulse radiolysis. Electrons are introduced into the enzyme initially at the [3Fe-4S] and ubiquinone sites followed by intramolecular equilibration with the b heme of the enzyme. To define thermodynamic and other controlling parameters for the pathways of electron transfer in complex II, site-directed variants were constructed and analyzed. Variants at SdhB-His207 and SdhB-Ile209 exhibit significantly perturbed electron transfer between the [3Fe-4S] cluster and ubiquinone. Analysis of the data using Marcus theory shows that the electronic coupling constants for wild-type and variant enzyme are all small, indicating that electron transfer occurs by diabatic tunneling. The presence of the ubiquinone is necessary for efficient electron transfer to the heme, which only slowly equilibrates with the [3Fe-4S] cluster in the absence of the quinone.
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland , Auckland 1142, New Zealand.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Anderson
authors.forename: Sujata S
authors.initials: SS
authors.lastname: Shinde
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.forename: Richard A
authors.initials: RA
authors.lastname: Rothery
authors.forename: Joel H
authors.initials: JH
authors.lastname: Weiner
authors.forename: Sany
authors.initials: S
authors.lastname: Rajagukguk
authors.forename: Elena
authors.initials: E
authors.lastname: Maklashina
authors.forename: Gary
authors.initials: G
authors.lastname: Cecchini
mesh_terms: D004579:Electron Transport; D042963:Electron Transport Complex II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014451:Ubiquinone / Q000737:chemistry / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D014451:Ubiquinone; D006418:Heme; D042963:Electron Transport Complex II