EC - Cystathionine γ-lyase

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IntEnz Enzyme Nomenclature


Accepted name:
cystathionine γ-lyase
Other names:
cysteine desulfhydrase
cysteine lyase
cystine desulfhydrase
homoserine deaminase
homoserine deaminase-cystathionase
homoserine dehydratase
L-cystathionine cysteine-lyase (deaminating)
Systematic name:
L-cystathionine cysteine-lyase (deaminating; 2-oxobutanoate-forming)




A multifunctional pyridoxal-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing L-cysteine and an unstable enamine product that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form 2-oxobutanoate and ammonia. The latter reaction, which can occur spontaneously, can also be catalysed by EC, 2-iminobutanoate/2-iminopropanoate deaminase. Also catalyses the conversion of L-homoserine to 2-oxobutanoate and ammonia, of L-cystine to thiocysteine, pyruvate and ammonia, and of L-cysteine to pyruvate, hydrogen sulfide and ammonia.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC00677
Structural data: CSA , EC2PDB
Gene Ontology: GO:0080146 , GO:0044540 , GO:0004123
CAS Registry Number: 9012-96-8
UniProtKB/Swiss-Prot: (14) [show] [UniProt]


  1. Braunstein, A.E. and Azarkh, R.M.
    [Participation of vitamin B6 in enzymic formation of hydrogen sulfide from L-cysteine.] (in Russian)
    Dokl. Akad. Nauk. S.S.S.R. 71 : 93-96 (1950).
  2. Braunstein, A.E. and Azarkh, R.M.
    [Phosphopyridoxal in aerobic deamination of homoserine and serine.] (in Russian)
    Dokl. Akad. Nauk. S.S.S.R. 85 : 385-388 (1952).
  3. Flavin, M. and Segal, A.
    Purification and properties of the cystathionine γ-cleavage enzyme of Neurospora.
    J. Biol. Chem. 239 : 2220-2227 (1964). [PMID: 14209951]
  4. Matsuo, Y. and Greenberg, D.M.
    A crystalline enzyme that cleaves homoserine and cystathionine. III. Coenzyme resolution, activation, and inhibitors.
    J. Biol. Chem. 234 : 507-515 (1959). [PMID: 13641250]
  5. Matsuo, Y. and Greenberg, D.M.
    A crystalline enzyme that cleaves homoserine and cystathionine. IV. Mechanism of action, reversibility, and substrate specificity.
    J. Biol. Chem. 234 : 516-519 (1959). [PMID: 13641251]

[EC created 1961 (EC created 1961, incorporated 1972)]