ExplorEnz: EC 4.4.1.1

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4.4.1.1

Accepted name:

cystathionine γ-lyase

Reaction:

L-cystathionine + H₂O = L-cysteine + 2-oxobutanoate + NH₃ (overall reaction)
(1a) L-cystathionine = L-cysteine + 2-aminobut-2-enoate
(1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous)
(1c) 2-iminobutanoate + H₂O = 2-oxobutanoate + NH₃ (spontaneous)

For diagram of reaction mechanism, click here

Other name(s):

homoserine deaminase; homoserine dehydratase; cystine desulfhydrase; cysteine desulfhydrase; γ-cystathionase; cystathionase; homoserine deaminase-cystathionase; γ-CTL; cystalysin; cysteine lyase; L-cystathionine cysteine-lyase (deaminating); CGL

Systematic name:

L-cystathionine cysteine-lyase (deaminating; 2-oxobutanoate-forming)

Comments:

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 3.5.99.10, 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:

BRENDA, EXPASY, Gene, KEGG, MetaCyc, PDB, CAS registry number: 9012-96-8

References:

1.	Braunstein, A.E. and Azarkh, R.M. [Participation of vitamin B₆ in enzymic formation of hydrogen sulfide from L-cysteine.] Dokl. Akad. Nauk S.S.S.R. 71 (1950) 93–96. (in Russian)
2.	Braunstein, A.E. and Azarkh, R.M. [Phosphopyridoxal in aerobic deamination of homoserine and serine.] Dokl. Akad. Nauk S.S.S.R. 85 (1952) 385–388. [PMID: 12998462] (in Russian)
3.	Flavin, M. and Segal, A. Purification and properties of the cystathionine γ-cleavage enzyme of Neurospora. J. Biol. Chem. 239 (1964) 2220–2227. [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 (1959) 507–515. [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 (1959) 516–519. [PMID: 13641251]

[EC 4.4.1.1 created 1961 (EC 4.2.1.15 created 1961, incorporated 1972)]