title: The role of mild uncoupling and non-coupled respiration in the regulation of hydrogen peroxide generation by plant mitochondria.
abstract: The roles of mild uncoupling caused by free fatty acids (mediated by plant uncoupling mitochondrial protein (PUMP) and ATP/ADP carrier (AAC)) and non-coupled respiration (alternative oxidase (AO)) on H(2)O(2) formation by plant mitochondria were examined. Both laurate and oleate prevent H(2)O(2) formation dependent on the oxidation of succinate. Conversely, these free fatty acids (FFA) only slightly affect that dependent on malate plus glutamate oxidation. Carboxyatractylate (CAtr), an inhibitor of AAC, completely inhibits oleate- or laurate-stimulated oxygen consumption linked to succinate oxidation, while GDP, an inhibitor of PUMP, caused only a 30% inhibition. In agreement, CAtr completely restores the oleate-inhibited H(2)O(2) formation, while GDP induces only a 30% restoration. Both oleate and laurate cause a mild uncoupling of the electrical potential (generated by succinate), which is then followed by a complete collapse with a sigmoidal kinetic. FFA also inhibit the succinate-dependent reverse electron transfer. Diamide, an inhibitor of AO, favors the malate plus glutamate-dependent H(2)O(2) formation, while pyruvate (a stimulator of AO) inhibits it. These results show that the succinate-dependent H(2)O(2) formation occurs at the level of Complex I by a reverse electron transport. This generation appears to be prevented by mild uncoupling mediated by FFA. The anionic form of FFA appears to be shuttled by AAC rather than PUMP. The malate plus glutamate-dependent H(2)O(2) formation is, conversely, mainly prevented by non-coupled respiration (AO).
authors.affiliation: Department of Biology and Agro-Industrial Economics, Section of Plant Biology, University of Udine, via Cotonificio 108, I-33100, Udine, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Casolo
authors.forename: E
authors.initials: E
authors.lastname: Braidot
authors.forename: E
authors.initials: E
authors.lastname: Chiandussi
authors.forename: F
authors.initials: F
authors.lastname: Macrì
authors.forename: A
authors.initials: A
authors.lastname: Vianello
mesh_terms: D001278:Atractyloside / Q000031:analogs & derivatives / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007473:Ion Channels; D007850:Lauric Acids / Q000494:pharmacology; D008293:Malates / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases / Q000037:antagonists & inhibitors / Q000378:metabolism; D024101:Mitochondrial Proteins; D019301:Oleic Acid / Q000494:pharmacology; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption; D018532:Pisum sativum / Q000648:ultrastructure*; D019802:Succinic Acid / Q000378:metabolism / Q000494:pharmacology; D014475:Uncoupling Agents / Q000378:metabolism; D000071256:Uncoupling Protein 1
chemical_list: D002352:Carrier Proteins; D007473:Ion Channels; D007850:Lauric Acids; D008293:Malates; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D014475:Uncoupling Agents; D000071256:Uncoupling Protein 1; C030358:lauric acid; D006153:Guanosine Diphosphate; D001278:Atractyloside; D019301:Oleic Acid; D018698:Glutamic Acid; C030298:malic acid; D000226:Mitochondrial ADP, ATP Translocases; D019802:Succinic Acid; D006861:Hydrogen Peroxide; C003853:carboxyatractyloside