The Enzyme Database

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Accepted name: cystathionine β-lyase
Reaction: L-cystathionine + H2O = L-homocysteine + pyruvate + NH3 (overall reaction)
(1a) L-cystathionine = L-homocysteine + 2-aminoprop-2-enoate
(1b) 2-aminoprop-2-enoate = 2-iminopropanoate (spontaneous)
(1c) 2-iminopropanoate + H2O = pyruvate + NH3 (spontaneous)
For diagram of L-Methionine biosynthesis, click here
Other name(s): β-cystathionase; cystine lyase; cystathionine L-homocysteine-lyase (deaminating); L-cystathionine L-homocysteine-lyase (deaminating); CBL
Systematic name: L-cystathionine L-homocysteine-lyase (deaminating; pyruvate-forming)
Comments: 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: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9055-05-4
1.  Anderson, N.W. and Thompson, J.F. Cystine lyase: β-cystathionase from turnip roots. Phytochemistry 18 (1979) 1953–1958.
2.  Flavin, M. and Slaughter, C. Cystathionine cleavage enzymes of Neurospora. J. Biol. Chem. 239 (1964) 2212–2219. [PMID: 14209950]
[EC created 1972]

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