Scheme 1.
CBS mediated enzymatic pathways. 1. The canonical activity of CBS is to produce cystathionine using serine and homocysteine as a substrates, cystathionine than can be converted to cysteine but this latter reaction is catalyzed by CSE. 2–3. CBS can also catalyze the generation of H2S by using homocysteine and cysteine as a substrates and/or using two cysteines to produce lanthionine. 4. Direct generation of Cys persulfide is catalyzed by CBS when cystine is used as a substrate, in this case Cys persulfide is generated without any involvement of H2S.