EC - Cystathionine β-lyase

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IntEnz Enzyme Nomenclature


Accepted name:
cystathionine β-lyase
Other names:
cystine lyase
cysteine lyase
β C-S lyase
cystathionine L-homocysteine-lyase (deaminating)
L-cystathionine L-homocysteine-lyase (deaminating)
Systematic name:
L-cystathionine L-homocysteine-lyase (deaminating; pyruvate-forming)




A pyridoxal-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing L-homocysteine 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, 2-iminobutanoate/2-iminopropanoate deaminase. The enzyme from some sources also acts on L-cystine, forming pyruvate, ammonia and cysteine persulfide, and a number of related compounds. Possibly identical, in yeast, with EC S-alkylcysteine lyase.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC00518 , PROSITE:PDOC00677
Structural data: CSA , EC2PDB
Gene Ontology: GO:0004121
CAS Registry Number: 9055-05-4
UniProtKB/Swiss-Prot: (24) [show] [UniProt]


  1. Anderson, N.W. and Thompson, J.F.
    Cystine lyase: β-cystathionase from turnip roots.
    Phytochemistry 18: 1953-1958 (1979).
  2. Flavin, M. and Slaughter, C.
    Cystathionine cleavage enzymes of Neurospora.
    J. Biol. Chem. 239: 2212-2219 (1964). [PMID: 14209950]

[EC created 1972]