Fig. 8.

Possible electron donation to the electron transport chain by H₂S. Notation: Cc: cytochrome c, where subscripts “ox” and “red” refer to the oxidation state of the heme proteine's iron center Fe(III) and Fe(II), respectively; CcO: cytochrome c oxidase; ETHE1: ethylmalonic encephalopathy 1 protein; GSH: glutathione; GSSH: glutathione persulfide; Q: ubiquinon; QH₂: ubiquinol; SQR: sulfide quinone oxidoreductase; SUOX: sulfite oxidase. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)