The enzyme cysteine lyase (EC 4.4.1.10) catalyzes the chemical reaction
This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is <small>L</small>-cysteine hydrogen-sulfide-lyase (adding sulfite; <small>L</small>-cysteate-forming). Other names in common use include cysteine (sulfite) lyase, and <small>L</small>-cysteine hydrogen-sulfide-lyase (adding sulfite). This enzyme participates in cysteine and taurine metabolism. It employs one cofactor, pyridoxal phosphate.
Genes encoding cysteine lyase (CL) originated around 300 million years ago by a tandem gene duplication and neofunctionalization of cystathionine ò-lyase (CBS) shortly after the split of mammalian and reptilian lineages. CL genes are found only in Sauropsida where they are involved in a metabolic pathway for sulfur metabolism in the chicken egg.