title: Mitochondrial diaphorases as NAD⁺ donors to segments of the citric acid cycle that support substrate-level phosphorylation yielding ATP during respiratory inhibition.
abstract: Substrate-level phosphorylation mediated by succinyl-CoA ligase in the mitochondrial matrix produces high-energy phosphates in the absence of oxidative phosphorylation. Furthermore, when the electron transport chain is dysfunctional, provision of succinyl-CoA by the α-ketoglutarate dehydrogenase complex (KGDHC) is crucial for maintaining the function of succinyl-CoA ligase yielding ATP, preventing the adenine nucleotide translocase from reversing. We addressed the source of the NAD(+) supply for KGDHC under anoxic conditions and inhibition of complex I. Using pharmacologic tools and specific substrates and by examining tissues from pigeon liver exhibiting no diaphorase activity, we showed that mitochondrial diaphorases in the mouse liver contribute up to 81% to the NAD(+) pool during respiratory inhibition. Under these conditions, KGDHC's function, essential for the provision of succinyl-CoA to succinyl-CoA ligase, is supported by NAD(+) derived from diaphorases. Through this process, diaphorases contribute to the maintenance of substrate-level phosphorylation during respiratory inhibition, which is manifested in the forward operation of adenine nucleotide translocase. Finally, we show that reoxidation of the reducible substrates for the diaphorases is mediated by complex III of the respiratory chain.
authors.affiliation: 1Department of Medical Biochemistry, Semmelweis University, 37-47 Tuzolto Street, Budapest 1094, Hungary. chinopoulos.christos@eok.sote.hu.
authors.forename: Gergely
authors.initials: G
authors.lastname: Kiss
authors.forename: Csaba
authors.initials: C
authors.lastname: Konrad
authors.forename: Issa
authors.initials: I
authors.lastname: Pour-Ghaz
authors.forename: Josef J
authors.initials: JJ
authors.lastname: Mansour
authors.forename: Beáta
authors.initials: B
authors.lastname: Németh
authors.forename: Anatoly A
authors.initials: AA
authors.lastname: Starkov
authors.forename: Vera
authors.initials: V
authors.lastname: Adam-Vizi
authors.forename: Christos
authors.initials: C
authors.lastname: Chinopoulos
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002952:Citric Acid Cycle; D010856:Columbidae; D008058:Dihydrolipoamide Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000860:Hypoxia / Q000378:metabolism; D007655:Ketoglutarate Dehydrogenase Complex / Q000037:antagonists & inhibitors / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008930:Mitochondria, Liver / Q000378:metabolism* / Q000502:physiology; D000226:Mitochondrial ADP, ATP Translocases / Q000378:metabolism; D008954:Models, Biological; D009243:NAD / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D013379:Substrate Specificity; D013389:Succinate-CoA Ligases / Q000378:metabolism; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D000214:Acyl Coenzyme A; D004791:Enzyme Inhibitors; D009570:Nitriles; D014475:Uncoupling Agents; D009243:NAD; C001784:SF 6847; D000255:Adenosine Triphosphate; D000226:Mitochondrial ADP, ATP Translocases; C012046:succinyl-coenzyme A; D007655:Ketoglutarate Dehydrogenase Complex; D008058:Dihydrolipoamide Dehydrogenase; D013389:Succinate-CoA Ligases
keywords: DT-diaphorase; adenine nucleotide translocase; reducing equivalent; succinyl-CoA ligase