title: Bypasses of the antimycin a block of mitochondrial electron transport in relation to ubisemiquinone function.
abstract: Two different bypasses around the antimycin block of electron transport from succinate to cytochrome c via the ubiquinol-cytochrome c oxidoreductase of intact rat liver mitochondria were analyzed, one promoted by N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and the other by 2,6-dichlorophenolindophenol (DCIP). Both bypasses are inhibited by myxothiazol, which blocks electron flow from ubiquinol to the Rieske iron-sulfur center, and by 2-hydroxy-3-undecyl-1,4-naphthoquinone, which inhibits electron flow from the iron-sulfur center to cytochrome c1. In the bypass promoted by TMPD its oxidized form (Wurster's blue) acts as an electron acceptor from some reduced component prior to the antimycin block, which by exclusion of other possibilities is ubisemiquinone. In the DCIP bypass its reduced form acts as an electron donor, by reducing ubisemiquinone to ubiquinol; reduced DCIP is regenerated again at the expense of either succinate or ascorbate. The observations described are consistent with and support current models of the Q cycle. Bypasses promoted by artificial electron carriers provide an independent approach to analysis of electron flow through ubiquinol-cytochrome c oxidoreductase.
mesh_terms: D015086:2,6-Dichloroindophenol / Q000494:pharmacology; D000818:Animals; D000968:Antimycin A / Q000494:pharmacology*; D003067:Coenzymes; D003573:Cytochrome b Group / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects; D014450:Electron Transport Complex III; D008689:Methacrylates; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D009285:Naphthoquinones / Q000494:pharmacology; D011808:Quinone Reductases / Q000378:metabolism; D051381:Rats; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid; D013772:Tetramethylphenylenediamine / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D003067:Coenzymes; D003573:Cytochrome b Group; D003574:Cytochrome c Group; D008689:Methacrylates; D009097:Multienzyme Complexes; D009285:Naphthoquinones; D013386:Succinates; D013844:Thiazoles; D014451:Ubiquinone; C039344:2-hydroxy-3-undecyl-1,4-naphthoquinone; D000968:Antimycin A; C030517:myxothiazol; D019802:Succinic Acid; D015086:2,6-Dichloroindophenol; D011808:Quinone Reductases; D014450:Electron Transport Complex III; C024989:coenzyme Q10; D013772:Tetramethylphenylenediamine