Mitochondrial cytochrome oxidase produces nitric oxide under hypoxic conditions: implications for oxygen sensing and hypoxic signaling in eukaryotes

Cell Metab. 2006 Apr;3(4):277-87. doi: 10.1016/j.cmet.2006.02.011.


Eukaryotic cells respond to low-oxygen concentrations by upregulating hypoxic nuclear genes (hypoxic signaling). Although it has been shown previously that the mitochondrial respiratory chain is required for hypoxic signaling, its underlying role in this process has been unclear. Here, we find that yeast and rat liver mitochondria produce nitric oxide (NO) at dissolved oxygen concentrations below 20 microM. This NO production is nitrite (NO2-) dependent, requires an electron donor, and is carried out by cytochrome c oxidase in a pH-dependent fashion. Mitochondrial NO production in yeast is influenced by the YHb flavohemoglobin NO oxidoreductase, stimulates expression of the hypoxic nuclear gene CYC7, and is accompanied by an increase in protein tyrosine nitration. These findings demonstrate an alternative role for the mitochondrial respiratory chain under hypoxic or anoxic conditions and suggest that mitochondrially produced NO is involved in hypoxic signaling, possibly via a pathway that involves protein tyrosine nitration.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Blotting, Northern
  • Cell Hypoxia*
  • Dioxygenases
  • Electron Transport / physiology
  • Electron Transport Complex IV / metabolism*
  • Electron Transport Complex IV / physiology
  • Electrophoresis, Polyacrylamide Gel
  • Gene Expression Regulation, Fungal
  • Hemeproteins / physiology
  • Hydrogen-Ion Concentration
  • Mitochondria / enzymology
  • Mitochondria / metabolism*
  • Mitochondria, Liver / enzymology
  • Mitochondria, Liver / metabolism*
  • Nitric Oxide / metabolism*
  • Nitrite Reductases / metabolism
  • Oxygen / analysis*
  • Rats
  • Rats, Inbred F344
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / physiology
  • Up-Regulation


  • Hemeproteins
  • Saccharomyces cerevisiae Proteins
  • Nitric Oxide
  • Dioxygenases
  • YHB1 protein, S cerevisiae
  • Nitrite Reductases
  • Electron Transport Complex IV
  • Oxygen