IUBMB Enzyme Nomenclature


Accepted name: cysteine synthase

Reaction: O-acetyl-L-serine + hydrogen sulfide = L-cysteine + acetate

For diagram of reaction click here.

Glossary: O-acetyl-L-serine = (2S)-3-acetyloxy-2-aminopropanoic acid

Other name(s): O-acetyl-L-serine sulfhydrylase; O-acetyl-L-serine sulfohydrolase; O-acetylserine (thiol)-lyase; O-acetylserine (thiol)-lyase A; O-acetylserine sulfhydrylase; O3-acetyl-L-serine acetate-lyase (adding hydrogen-sulfide); acetylserine sulfhydrylase; cysteine synthetase; S-sulfocysteine synthase

Systematic name: O-acetyl-L-serine:hydrogen-sulfide 2-amino-2-carboxyethyltransferase

Comments: A pyridoxal-phosphate protein. Some alkyl thiols, cyanide, pyrazole and some other heterocyclic compounds can act as acceptors. Not identical with EC (β-pyrazolylalanine synthase), EC (L-mimosine synthase) and EC (uracilylalanine synthase).

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 37290-89-4


1. Becker, M.A., Kredich, N.M. and Tomkins, G.M. The purification and characterization of O-acetylserine sulfhydrylase-A from Salmonella typhimurium. J. Biol. Chem. 244 (1969) 2418-2427. [PMID: 4891157]

2. Hara, S., Payne, M.A., Schnackerz, K.D. and Cook, P.F. A rapid purification procedure and computer-assisted sulfide ion selective electrode assay for O-acetylserine sulfhydrylase from Salmonella typhimurium. Protein Expr. Purif. 1 (1990) 70-76. [PMID 2152186]

3. Ikegami, F., Kaneko, M., Lambein, F., Kuo, Y.-H. and Murakoshi, I. Difference between uracilylalanine synthases and cysteine synthases in Pisum sativum. Phytochemistry 26 (1987) 2699-2704.

4. Murakoshi, I., Kaneko, M., Koide, C. and Ikegami, F. Enzymatic-synthesis of the neuroexcitatory amino-acid quisqualic by cysteine synthase. Phytochemistry 25 (1986) 2759-2763.

5. Tai, C.H., Burkhard, P., Gani, D., Jenn, T., Johnson, C. and Cook, P.F. Characterization of the allosteric anion-binding site of O-acetylserine sulfhydrylase. Biochemistry 40 (2001) 7446-7452. [PMID: 11412097]

6. Bettati, S., Benci, S., Campanini, B., Raboni, S., Chirico, G., Beretta, S., Schnackerz, K.D., Hazlett, T.L., Gratton, E. and Mozzarelli, A. Role of pyridoxal 5'-phosphate in the structural stabilization of O-acetylserine sulfhydrylase. J. Biol. Chem. 275 (2000) 40244-40251. [PMID: 10995767]

[EC created 1972 as EC, modified 1976, modified 1990, transferred 2002 to EC]

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