Figure 7.

Mitochondrial sulfide-oxidizing pathway. Scheme depicting the enzymatic components and metabolites involved in sulfide oxidation in the mitochondria. H₂S is initially oxidized by sulfide:quinone oxidoreductase (SQR), which transfers electron equivalents to quinones and generates glutathione persulfide (GSSH) as coproduct. Electrons are transferred to O₂ via complex III (c.III), cytochrome c (Cc), and complex IV (c.IV), contributing to membrane energization and ATP synthesis. GSSH, with O₂ as cosubstrate, is then converted by persulfide dioxygenase (ETHE1) to sulfite (SO₃²⁻) and GSH. Sulfite can be converted, with GSSH as cosubstrate, into thiosulfate (S₂O₃²⁻) by rhodanese (Rhod), or oxidized into sulfate (SO₄²⁻) by sulfite oxidase (SOx).