title: Complete inhibition of dihydro-orotate oxidation and superoxide production by 1,1,1-trifluoro-3-thenoylacetone in rat liver mitochondria.
abstract: 1,1,1-Trifluoro-3-thenoylacetone was shown to cause complete inhibition of dihydroorotate oxidation in rat liver mitochondria as measured by orotate formation and the rate of dihydro-orotate-dependent reduction of 2,6-dichlorophenol-indophenol or cytochrome c. The inhibition by trifluorothenoylacetone was dose-dependent, and a concentration of 1 mM completely inhibited dihydro-orotate dehydrogenase activity. 1,10-Phenanthroline, another iron-chelating agent, also caused total inhibition of the liver enzyme. Whereas the iron chelators inhibited 100% of dihydro-orotate dehydrogenase activity in liver mitochondria, they inhibited only a maximum of 72% in the case of the brain enzyme. The inhibition by trifluorothenoylacetone was not prevented by addition of phenazine methosulphate or ubiquinone. Dihydro-orotate dehydrogenase-mediated generation of superoxide was abolished when the enzyme was fully inhibited by trifluorothenoylacetone or when the electron-transport system was blocked by antimycin A. These results suggest that the iron component(s) of dihydro-orotate dehydrogenase is of strategic importance for catalytic activity and transfer of reducing equivalents from the primary enzyme to the electron-transport chain. Furthermore, the study indicates that production of superoxide radicals during dihydro-orotate dehydrogenase-catalysed oxidation of dihydro-orotate may be at the cytochrome b-c1 segment of the electron-transport chain (as a consequence of autooxidation of ubisemiquinone) rather than at a site on the primary enzyme.
authors.forename: K N
authors.initials: KN
authors.lastname: Dileepan
authors.forename: J
authors.initials: J
authors.lastname: Kennedy
mesh_terms: D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D003574:Cytochrome c Group / Q000378:metabolism; D004081:Dihydroorotate Oxidase / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D051381:Rats; D011919:Rats, Inbred Strains; D013482:Superoxide Dismutase / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology*; D013876:Thiophenes / Q000494:pharmacology*
chemical_list: D003574:Cytochrome c Group; D013876:Thiophenes; D013481:Superoxides; D013804:Thenoyltrifluoroacetone; D000968:Antimycin A; D010088:Oxidoreductases; D013482:Superoxide Dismutase; D004081:Dihydroorotate Oxidase