Figure 3. Hydrogen sulfide biosynthesis, signalling and regulation.
As described in the text, H2S is synthesised by diverse pathways from cysteine and cystathionine, but also readily permeates membranes in the unionised form. Specific H2S synthesis enzymes include cystathionine-β-synthase (CBS), cystathionine-γ-synthase (CSE) and the 3-mercaptopyruvate sulfurtransferase/cysteine aminotransferase (3-MST/CAT) pathway. Persulfides (e.g. CysSSR) are key to H2S signalling pathways. CstR is a persulfide-sensing sulfide stress-response regulator in S. aureus.