title: Menaquinone-dependent succinate dehydrogenase of bacteria catalyzes reversed electron transport driven by the proton potential.
abstract: Succinate dehydrogenases from bacteria and archaea using menaquinone (MK) as an electron acceptor (succinate/menaquinone oxidoreductases) contain, or are predicted to contain, two heme-B groups in the membrane-anchoring protein(s), located close to opposite sides of the membrane. All succinate/ubiquinone oxidoreductases, however, contain only one heme-B molecule. In Bacillus subtilis and other bacteria that use MK as the respiratory quinone, the succinate oxidase activity (succinate-->O2), and the succinate/menaquinone oxidoreductase activity were specifically inhibited by uncoupler (CCCP, carbonyl cyanide m-chlorophenylhydrazone) or by agents dissipating the membrane potential (valinomycin). Other parts of the respiratory chains were not affected by the agents. Succinate oxidase or succinate/ubiquinone oxidoreductase from bacteria using ubiquinone as an acceptor were not inhibited. We propose that the endergonic electron transport from succinate (Eo' = +30 mV) to MK (Eo' approximately/= -80 mV) in succinate/menaquinone oxidoreductase includes a reversed electron transport across the cytoplasmic membrane from the inner (negative) to the outer (positive) side via the two heme-B groups. The reversed electron transport is driven by the proton or electrical potential, which provides the driving force for MK reduction.
authors.affiliation: Institut für Mikrobiologie und Weinforschung, Universität Mainz, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Schirawski
authors.forename: G
authors.initials: G
authors.lastname: Unden
mesh_terms: D001419:Bacteria / Q000201:enzymology*; D001665:Binding Sites; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002384:Catalysis; D004563:Electrochemistry; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006418:Heme / Q000378:metabolism; D008564:Membrane Potentials; D011522:Protons; D013385:Succinate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014812:Vitamin K / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D011522:Protons; D014812:Vitamin K; D006418:Heme; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D013385:Succinate Dehydrogenase