Figure 1. Mitochondrial H2S oxidation pathway.

SQR converts sulfide into thiosulfate by transferring two electrons from the H2S oxidation to ubiquinone (CoQ). Thiosulfate is then converted into sulfite by TST and ETHE1; this reaction requires a sulfur acceptor (glutathione, GSH). Excess of sulfite is converted into sulfate by SUOX.