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The enzyme cysteine lyase (EC 4.4.1.10) catalyzes the chemical reaction

L-cysteine + sulfite ${\displaystyle \rightleftharpoons }$ L-cysteate + hydrogen sulfide

This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is L-cysteine hydrogen-sulfide-lyase (adding sulfite; L-cysteate-forming). Other names in common use include cysteine (sulfite) lyase, and L-cysteine hydrogen-sulfide-lyase (adding sulfite). This enzyme participates in cysteine and taurine metabolism. It employs one cofactor, pyridoxal phosphate.

Evolution

Genes encoding cysteine lyase (CL) originated around 300 million years ago by a tandem gene duplication and neofunctionalization of cystathionine β-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.

References

1. Tolosa EA, Chepurnova NK, Khomutov RM, Severin ES (1969). "Reactions catalysed by cysteine lyase from the yolk sac of chicken embryo". Biochim. Biophys. Acta. 171 (2): 369–71. doi:10.1016/0005-2744(69)90174-0. PMID 5813025.
2. Malatesta M, Mori G, Acquotti D, Campanini B, Peracchi A, Antin PB, Percudani R (2020). "Birth of a pathway for sulfur metabolism in early amniote evolution". Nat Ecol Evol. 4 (9): 1239–1246. Bibcode:2020NatEE...4.1239M. doi:10.1038/s41559-020-1232-4. PMC 8364350. PMID 32601391.

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