title: Enhancement of hydrogen peroxide formation by protophores and ionophores in antimycin-supplemented mitochondria.
abstract: Rat and pigeon heart mitochondria supplemented with antimycin produce 0.3-1.0nmol of H(2)O(2)/min per mg of protein. These rates are stimulated up to 13-fold by addition of protophores (carbonyl cyanide p-trifluoromethoxyphenylhydrazone, carbonyl cyanide m-chloromethoxyphenylhydrazone and pentachlorophenol). Ionophores, such as valinomycin and gramicidin, and Ca(2+) also markedly stimulated H(2)O(2) production by rat heart mitochondria. The enhancement of H(2)O(2) generation in antimycin-supplemented mitochondria and the increased O(2) uptake of the State 4-to-State 3 transition showed similar protophore, ionophore and Ca(2+) concentration dependencies. Thenoyltrifluoroacetone and N-bromosuccinimide, which inhibit succinate-ubiquinone reductase activity, also decreased mitochondrial H(2)O(2) production. Addition of cyanide to antimycin-supplemented beef heart submitochondrial particles inhibited the generation of O(2) (-), the precursor of mitochondrial H(2)O(2). This effect was parallel to the increase in cytochrome c reduction and it is interpreted as indicating the necessity of cytochrome c(1) (3+) to oxidize ubiquinol to ubisemiquinone, whose autoxidation yields O(2) (-). The effect of protophores, ionophores and Ca(2+) is analysed in relation to the propositions of a cyclic mechanism for the interaction of ubiquinone with succinate dehydrogenase and cytochromes b and c(1) [Wikstrom & Berden (1972) Biochim. Biophys. Acta283, 403-420; Mitchell (1976) J. Theor. Biol.62, 337-367]. A collapse in membrane potential, increasing the rate of ubisemiquinone formation and O(2) (-) production, is proposed as the molecular mechanism for the enhancement of H(2)O(2) formation rates observed on addition of protophores, ionophores and Ca(2+).
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001974:Bromosuccinimide / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology*; D010856:Columbidae; D006861:Hydrogen Peroxide / Q000378:metabolism*; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology*; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology*; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology
chemical_list: D007476:Ionophores; D009570:Nitriles; D013804:Thenoyltrifluoroacetone; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000968:Antimycin A; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D001974:Bromosuccinimide; D011190:Potassium Cyanide; D002118:Calcium