IUBMB Enzyme Nomenclature


Accepted name: S-sulfo-L-cysteine synthase (O-acetyl-L-serine-dependent)

Reaction: O-acetyl-L-serine + thiosulfate = S-sulfo-L-cysteine + acetate

For diagram of reaction click here.

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

Other name(s): cysteine synthase B; cysM (gene name); CS26 (gene name)

Systematic name: O-acetyl-L-serine:thiosulfate 2-amino-2-carboxyethyltransferase

Comments: In plants, the activity is catalysed by a chloroplastic enzyme that plays an important role in chloroplast function and is essential for light-dependent redox regulation within the chloroplast. The bacterial enzyme also catalyses the activity of EC, cysteine synthase. cf. EC, S-sulfo-L-cysteine synthase (3-phospho-L-serine-dependent).

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Hensel, G. and Truper, H.G. O-Acetylserine sulfhydrylase and S-sulfocysteine synthase activities of Rhodospirillum tenue. Arch. Microbiol. 134 (1983) 227-232. [PMID: 6615127]

2. Nakamura, T., Iwahashi, H. and Eguchi, Y. Enzymatic proof for the identity of the S-sulfocysteine synthase and cysteine synthase B of Salmonella typhimurium. J. Bacteriol. 158 (1984) 1122-1127. [PMID: 6373737]

3. Bermudez, M.A., Paez-Ochoa, M.A., Gotor, C. and Romero, L.C. Arabidopsis S-sulfocysteine synthase activity is essential for chloroplast function and long-day light-dependent redox control. Plant Cell 22 (2010) 403-416. [PMID: 20179139]

4. Bermudez, M.A., Galmes, J., Moreno, I., Mullineaux, P.M., Gotor, C. and Romero, L.C. Photosynthetic adaptation to length of day is dependent on S-sulfocysteine synthase activity in the thylakoid lumen. Plant Physiol. 160 (2012) 274-288. [PMID: 22829322]

5. Gotor, C. and Romero, L.C. S-sulfocysteine synthase function in sensing chloroplast redox status. Plant Signal Behav 8 (2013) e23313. [PMID: 23333972]

[EC created 2018]

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