Reaction: L-cystine + H2O = L-thiocysteine + pyruvate + NH3 (overall reaction)
(1a) L-cystine = L-thiocysteine + 2-aminoprop-2-enoate
(1b) 2-aminoprop-2-enoate = 2-iminopropanoate (spontaneous)
(1c) 2-iminopropanoate + H2O = pyruvate + NH3 (spontaneous)
Glossary: L-thiocysteine = S-sulfanyl-L-cysteine
Other name(s): CORI3 (gene name)
Systematic name: L-cystine thiocysteine-lyase (deaminating; pyruvate-forming)
Comments: A pyridoxal 5'-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing L-thiocysteine 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. The enzyme from Brassica oleracea var. italica (broccoli) does not act on cysteine or cystathionine.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Ukai, K. and Sekiya, J. Purification and characterization of cystine lyase a from broccoli Inflorescence. Biosci. Biotechnol. Biochem. 61 (1997) 1890-1895. [PMID: 27396740]
2. Jones, P.R., Manabe, T., Awazuhara, M. and Saito, K. A new member of plant CS-lyases. A cystine lyase from Arabidopsis thaliana. J. Biol. Chem. 278 (2003) 10291-10296. [PMID: 12525491]