FIGURE 1.

H₂S biogenesis and catabolism. a, The enzymes in the transsulfuration pathway, CBS and CSE, catalyze multiple H₂S-producing reactions, and the dominant reaction is shown in red. CAT and MST are components of the cysteine catabolism pathway. The preferred sulfur acceptor of MST is not known. b, components of the mitochondrial sulfide oxidation pathway that couple to the electron transfer chain. Q is ubiquinone. This figure was adapted from Ref. 30.