Nitrogen dioxide oxidizes mitochondrial cytochrome c

► Nitric oxide has been previously reported to oxidize mitochondrial cytochrome c. ► We now show that this reaction is oxygen concentration dependent. ► Nitrogen dioxide scavengers (urate; ferrocyanide) modulate the oxidation. ► We construct a kinetic model consistent with nitrogen dioxide as the oxidizing species. ► The model predicts a rate constant for cytochrome c oxidation of 3 × 106 M-1 s-1.