Reaction: L-cysteate + H2O = HSO3– + pyruvate + NH3 (overall reaction)
(1a) L-cysteate = HSO3– + 2-aminoprop-2-enoate
(1b) 2-aminoprop-2-enoate = 2-iminopropanoate (spontaneous)
(1c) 2-iminopropanoate + H2O = pyruvate + NH3 (spontaneous)
Glossary: L-cysteate = (2S)-2-amino-3-sulfopropanoate
bisulfite = HSO3–
Other name(s): L-cysteate sulfo-lyase (deaminating); CuyA
Systematic name: L-cysteate bisulfite-lyase (deaminating; pyruvate-forming)
Comments: A pyridoxal-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing bisulfite and an unstable enamine product that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form pyruvate and ammonia. The latter reaction, which can occur spontaneously, can also be catalysed by EC 3.5.99.10, 2-iminobutanoate/2-iminopropanoate deaminase. D-Cysteine can also act as a substrate, but more slowly. It is converted into hydrogen sulfide, pyruvate, and ammonia. This inducible enzyme from the marine bacterium Silicibacter pomeroyi DSS-3 forms part of the cysteate-degradation pathway.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
References:
1. Denger, K., Smits, T.H. and Cook, A.M. L-cysteate sulpho-lyase, a widespread, pyridoxal 5'-phosphate-coupled desulphonative enzyme purified from Silicibacter pomeroyi DSS-3 T. Biochem. J. 394 (2005) 657-664. [PMID: 16302849]