Ravasz 2018 Biochim Biophys Acta

Ravasz D, Kacso G, Fodor V, Horvath K, Adam-Vizi V, Chinopoulos C (2018) Reduction of 2-methoxy-1,4-naphtoquinone by mitochondrially-localized Nqo1 yielding NAD+ supports substrate-level phosphorylation during respiratory inhibition. Biochim Biophys Acta 1859:909-24.

» PMID: 29746824 Open Access

Ravasz D, Kacso G, Fodor V, Horvath K, Adam-Vizi V, Chinopoulos C (2018) Biochim Biophys Acta

Abstract: Provision of NAD⁺ for oxidative decarboxylation of alpha-ketoglutarate to succinyl-CoA by the ketoglutarate dehydrogenase complex (KGDHC) is critical for maintained operation of succinyl-CoA ligase yielding high-energy phosphates, a process known as mitochondrial substrate-level phosphorylation (mSLP). We have shown previously that when NADH oxidation by complex I is inhibited by rotenone or anoxia, mitochondrial diaphorases yield NAD⁺, provided that suitable quinones are present (Kiss G et al., FASEB J 2014, 28:1682). This allows for KGDHC reaction to proceed and as an extension of this, mSLP. NAD(P)H quinone oxidoreductase 1 (NQO1) is an enzyme exhibiting diaphorase activity. Here, by using Nqo1^-/- and WT littermate mice we show that in rotenone-treated, isolated liver mitochondria 2-methoxy-1,4-naphtoquinone (MNQ) is preferentially reduced by matrix Nqo1 yielding NAD⁺ to KGDHC, supporting mSLP. This process was sensitive to inhibition by specific diaphorase inhibitors. Reduction of idebenone and its analogues MRQ-20 and MRQ-56, menadione, mitoquinone and duroquinone were unaffected by genetic disruption of the Nqo1 gene. The results allow for the conclusions that i) MNQ is a Nqo1-preferred substrate, and ii) in the presence of suitable quinones, mitochondrially-localized diaphorases other than Nqo1 support NADH oxidation when complex I is inhibited. Our work confirms that complex I bypass can occur by quinones reduced by intramitochondrial diaphorases oxidizing NADH, ultimately supporting mSLP. Finally, it may help to elucidate structure-activity relationships of redox-active quinones with diaphorase enzymes.

• Bioblast editor: Kandolf G • O2k-Network Lab: HU Budapest Chinopoulos C

Labels: MiParea: Respiration, nDNA;cell genetics 

Organism: Mouse  Tissue;cell: Liver  Preparation: Isolated mitochondria 

Coupling state: LEAK, OXPHOS  Pathway: F, N, DQ  HRR: Oxygraph-2k, O2k-Fluorometer 

Labels, 2018-07, Safranine-O