EC - Cysteine-S-conjugate β-lyase

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IntEnz Enzyme Nomenclature


Accepted name:
cysteine-S-conjugate β-lyase
Other names:
cysteine conjugate β-lyase
glutamine transaminase K/cysteine conjugate β-lyase
L-cysteine-S-conjugate thiol-lyase (deaminating)
Systematic name:
L-cysteine-S-conjugate thiol-lyase (deaminating; pyruvate-forming)




A pyridoxal 5′-phosphate protein. This mammalian enzyme has been shown to act on many substrates, including aromatic compounds such as S-(4-bromophenyl)-L-cysteine and S-(2,4-dinitrophenyl)-L-cysteine. The enzyme cleaves a carbon-sulfur bond, releasing a thiol and an unstable enamine product that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form pyruvate and ammonia. All of the cysteine-S-conjugate β-lyases discovered thus far are bifunctional enzymes, most of which also act as aminotransferases. Despite some overlap in their activity, this enzyme is not identical to the bacterial EC, cystathionine β-lyase.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0047804
CAS Registry Number: 68652-57-3


  1. Tateishi, M., Suzuki, S. and Shimizu, H.
    Cysteine conjugate β-lyase in rat liver. A novel enzyme catalyzing formation of thiol-containing metabolites of drugs.
    J. Biol. Chem. 253: 8854-8859 (1978). [PMID: 721818]
  2. Stevens, J. L.
    Isolation and characterization of a rat liver enzyme with both cysteine conjugate beta-lyase and kynureninase activity.
    J. Biol. Chem. 260: 7945-7950 (1985). [PMID: 4008484]
  3. Stevens, J. L., Robbins, J. D., Byrd, R. A.
    A purified cysteine conjugate beta-lyase from rat kidney cytosol. Requirement for an alpha-keto acid or an amino acid oxidase for activity and identity with soluble glutamine transaminase K.
    J. Biol. Chem. 261: 15529-15537 (1986). [PMID: 3782077]
  4. Gaskin, P. J., Adcock, H. J., Buckberry, L. D., Teesdale-Spittle, P. H., Shaw, P. N.
    The C-S lysis of L-cysteine conjugates by aspartate and alanine aminotransferase enzymes.
    Hum Exp Toxicol 14: 422-427 (1995). [PMID: 7612304]
  5. Cooper, A. J., Bruschi, S. A., Iriarte, A., Martinez-Carrion, M.
    Mitochondrial aspartate aminotransferase catalyses cysteine S-conjugate beta-lyase reactions.
    Biochem. J. 368: 253-261 (2002). [PMID: 12137566]
  6. Cooper, A. J., Bruschi, S. A., Conway, M., Hutson, S. M.
    Human mitochondrial and cytosolic branched-chain aminotransferases are cysteine S-conjugate beta-lyases, but turnover leads to inactivation.
    Biochem. Pharmacol. 65: 181-192 (2003). [PMID: 12504794]
  7. Cooper, A. J., Pinto, J. T.
    Cysteine S-conjugate beta-lyases.
    Amino Acids 30: 1-15 (2006). [PMID: 16463021]

[EC created 1981]