title: The interaction of quinone analogues with wild-type and ubiquinone-deficient yeast mitochondria.
abstract: The interaction of the exogenous quinones, duroquinone (DQ) and the decyl analogue of ubiquinone (DB) with the mitochondrial respiratory chain was studied in both wild-type and a ubiquinone-deficient mutant of yeast. DQ can be reduced directly by NADH dehydrogenase, but cannot be reduced by succinate dehydrogenase in the absence of endogenous ubiquinone. The succinate-driven reduction of DQ can be stimulated by DB in a reaction inhibited 50% by antimycin and 70-80% by the combined use of antimycin and myxothiazol, suggesting that electron transfer occurs via the cytochrome b-c1 complex. Both DQ and DB can effectively mediate the reduction of cytochrome b by the primary dehydrogenases through center o, but their ability to mediate the reduction of cytochrome b through center i is negligible. Two reaction sites for ubiquinol seem to be present at center o: one is independent of endogenous Q6 with a high reaction rate and a high Km; the other is affected by endogenous Q6 and has a low reaction rate and a low Km. By contrast, only one ubiquinol reaction site was observed at center i, where DB appears to compete with endogenous Q6. DB can oxidize most of the pre-reduced cytochrome b, while DQ can oxidize only 50%. On the basis of these data, the possible binding patterns of DB on different Q-reaction sites and the requirement for ubiquinone in the continuous oxidation of DQH are discussed.
authors.affiliation: Department of Biochemistry, West Virginia University School of Medicine, Morgantown 26506.
authors.forename: Q S
authors.initials: QS
authors.lastname: Zhu
authors.forename: D S
authors.initials: DS
authors.lastname: Beattie
mesh_terms: D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D016227:Benzoquinones; D003573:Cytochrome b Group / Q000378:metabolism; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000378:metabolism; D007700:Kinetics; D008689:Methacrylates; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D011809:Quinones / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism*; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid; D013844:Thiazoles / Q000494:pharmacology; D014451:Ubiquinone / Q000502:physiology*
chemical_list: D016227:Benzoquinones; D003573:Cytochrome b Group; D008689:Methacrylates; D011809:Quinones; D013386:Succinates; D013844:Thiazoles; C032456:antimycin; D014451:Ubiquinone; D000968:Antimycin A; C030517:myxothiazol; D019802:Succinic Acid; D013385:Succinate Dehydrogenase; D014450:Electron Transport Complex III; C034257:duroquinone