Ravasz 2018 Abstract The evolving concept of mitochondria
|Vast pools of endogenous quinones sustain NADH oxidation by Complex I during anoxia, supporting substrate-level phosphorylation in mouse liver mitochondria.
Anoxia leads to over-reduction of mitochondrial quinone pools hampering Complex I from oxidizing NADH, leading to a profound decrease in the matrix NAD+/NADH ratio. As a consequence of this, the function of matrix dehydrogenases is impaired. Yet, under certain anoxic conditions catabolism of metabolites converging through the ketoglutarate dehydrogenase Complex (KGDHC) is known to occur yielding succinyl-CoA, in turn supporting substrate-level phosphorylation substantiated by succinate-CoA ligase. Here, by measuring simultaneously oxygen partial pressure and NADH autofluorescence or quinone redox state we show that in isolated mitochondria Complex I utilizes endogenous quinones oxidizing NADH during anoxia. Untargeted metabolomic analysis of matrix metabolites of anoxic mitochondria and in the presence of ETC inhibitors inferred that NAD+ arising from Complex I is utilized by KGDHC yielding succinyl-CoA for succinate-CoA ligase, thus maintaining substrate-level phosphorylation during anoxia. The amount of endogenous quinones was estimated to be in the millimolar range and was unaffected by dietary intake of vitamin K3 (menadione). The quinone pools could be reduced by Complexes I and II and the electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) system during anoxia, exhibiting a descending order of affinity and reciprocally, increasing order of capacity. Our results highlight the importance of quinone availability in conjunction to Complex I-mediated NADH oxidation in maintaining substrate-level phosphorylation during anoxia.
Labels: MiParea: Respiration Pathology: Other
Organism: Mouse Tissue;cell: Liver Preparation: Isolated mitochondria Enzyme: Complex I, TCA cycle and matrix dehydrogenases Regulation: Redox state, Substrate, Q-junction effect Coupling state: LEAK, OXPHOS Pathway: N HRR: Oxygraph-2k, O2k-Fluorometer