Accepted name: cysteate synthase
Reaction: O-phospho-L-serine + sulfite = L-cysteate + phosphate
Other name(s): sulfite:O-phospho-L-serine sulfotransferase (phosphate-hydrolysing, L-cysteate-forming)
Systematic name: sulfite:O-phospho-L-serine sulfonotransferase (phosphate-hydrolysing, L-cysteate-forming)
Comments: A pyridoxal-phosphate protein. It is highly specific for O-phospho-L-serine and sulfite. The reaction proceeds through a dehydroalanine (2-aminoacrylic acid) intermediate. The enzyme from Methanosarcina acetivorans is evolutionarily related to threonine synthase (EC, but the reaction is more similar to that of O-phosphoserine sulfhydrylase (EC
1.  Graham, D.E., Taylor, S.M., Wolf, R.Z. and Namboori, S.C. Convergent evolution of coenzyme M biosynthesis in the Methanosarcinales: cysteate synthase evolved from an ancestral threonine synthase. Biochem. J. 424 (2009) 467–478. [PMID: 19761441]
[EC created 2009]
Accepted name: phosphoserine transaminase
Reaction: (1) O-phospho-L-serine + 2-oxoglutarate = 3-phosphooxypyruvate + L-glutamate
(2) 4-phosphooxy-L-threonine + 2-oxoglutarate = (3R)-3-hydroxy-2-oxo-4-phosphooxybutanoate + L-glutamate
Other name(s): PSAT; phosphoserine aminotransferase; 3-phosphoserine aminotransferase; hydroxypyruvic phosphate-glutamic transaminase; L-phosphoserine aminotransferase; phosphohydroxypyruvate transaminase; phosphohydroxypyruvic-glutamic transaminase; 3-O-phospho-L-serine:2-oxoglutarate aminotransferase; SerC; PdxC; 3PHP transaminase
Systematic name: O-phospho-L-serine:2-oxoglutarate aminotransferase
Comments: A pyridoxal 5′-phosphate protein. This enzyme catalyses the second step in the phosphorylated pathway of serine biosynthesis [1,3] and the third step in pyridoxal 5′-phosphate biosynthesis in the bacterium Escherichia coli [3]. Pyridoxal 5′-phosphate is the cofactor for both activities and therefore seems to be involved in its own biosynthesis [4]. Non-phosphorylated forms of serine and threonine are not substrates [4]. The archaeal enzyme has a relaxed specificity and can act on L-cysteate and L-alanine as alternative substrates to O-phospho-L-serine [7].
1.  Pizer, L.I. The pathway and control of serine biosynthesis in Escherichia coli. J. Biol. Chem. 238 (1963) 3934–3944. [PMID: 14086727]
2.  Hirsch, H. and Greenberg, D.M. Studies on phosphoserine aminotransferase of sheep brain. J. Biol. Chem. 242 (1967) 2283–2287. [PMID: 6022873]
3.  Zhao, G. and Winkler, M.E. A novel α-ketoglutarate reductase activity of the serA-encoded 3-phosphoglycerate dehydrogenase of Escherichia coli K-12 and its possible implications for human 2-hydroxyglutaric aciduria. J. Bacteriol. 178 (1996) 232–239. [PMID: 8550422]
4.  Drewke, C., Klein, M., Clade, D., Arenz, A., Müller, R. and Leistner, E. 4-O-phosphoryl-L-threonine, a substrate of the pdxC(serC) gene product involved in vitamin B6 biosynthesis. FEBS Lett. 390 (1996) 179–182. [PMID: 8706854]
5.  Zhao, G. and Winkler, M.E. 4-Phospho-hydroxy-L-threonine is an obligatory intermediate in pyridoxal 5′-phosphate coenzyme biosynthesis in Escherichia coli K-12. FEMS Microbiol. Lett. 135 (1996) 275–280. [PMID: 8595869]
6.  Baek, J.Y., Jun, D.Y., Taub, D. and Kim, Y.H. Characterization of human phosphoserine aminotransferase involved in the phosphorylated pathway of L-serine biosynthesis. Biochem. J. 373 (2003) 191–200. [PMID: 12633500]
7.  Helgadottir, S., Rosas-Sandoval, G., Soll, D. and Graham, D.E. Biosynthesis of phosphoserine in the Methanococcales. J. Bacteriol. 189 (2007) 575–582. [PMID: 17071763]
[EC created 1972, modified 2006]
Accepted name: glutamate decarboxylase
Reaction: L-glutamate = 4-aminobutanoate + CO2
Glossary: 4-aminobutanoate = γ-aminobutyrate = GABA
Other name(s): L-glutamic acid decarboxylase; L-glutamic decarboxylase; cysteic acid decarboxylase; L-glutamate α-decarboxylase; aspartate 1-decarboxylase; aspartic α-decarboxylase; L-aspartate-α-decarboxylase; γ-glutamate decarboxylase; L-glutamate 1-carboxy-lyase
Systematic name: L-glutamate 1-carboxy-lyase (4-aminobutanoate-forming)
Comments: A pyridoxal-phosphate protein. The brain enzyme also acts on L-cysteate, 3-sulfino-L-alanine and L-aspartate.
1.  Ambe, L. and Sohonie, K. Purification and properties of glutamate decarboxylase from the field bean (Dolichos lablab). Enzymologia 26 (1963) 98–107. [PMID: 14081858]
2.  Nakano, Y. and Kitaoka, S. L-Aspartate α-decarboxylase in a cell-free system from Escherichia coli. J. Biochem. (Tokyo) 70 (1971) 327. [PMID: 4937550]
3.  Roberts, E. and Frankel, S. Further studies of glutamic acid decarboxylase in brain. J. Biol. Chem. 190 (1951) 505–512. [PMID: 14841200]
[EC created 1961]
Accepted name: sulfinoalanine decarboxylase
Reaction: 3-sulfino-L-alanine = hypotaurine + CO2
Other name(s): cysteine-sulfinate decarboxylase; L-cysteinesulfinic acid decarboxylase; cysteine-sulfinate decarboxylase; CADCase/CSADCase; CSAD; cysteic decarboxylase; cysteinesulfinic acid decarboxylase; cysteinesulfinate decarboxylase; sulfoalanine decarboxylase; 3-sulfino-L-alanine carboxy-lyase
Systematic name: 3-sulfino-L-alanine carboxy-lyase (hypotaurine-forming)
Comments: A pyridoxal-phosphate protein. Also acts on L-cysteate. The 1992 edition of the Enzyme List erroneously gave the name sulfoalanine decarboxylase to this enzyme.
1.  Guion-Rain, M.C., Portemer, C. and Chatagner, F. Rat liver cysteine sulfinate decarboxylase: purification, new appraisal of the molecular weight and determination of catalytic properties. Biochim. Biophys. Acta 384 (1975) 265–276. [PMID: 236774]
2.  Jacobsen, J.G., Thomas, L.L. and Smith, L.H., Jr. Properties and distribution of mammalian L-cysteine sulfinate carboxy-lyases. Biochim. Biophys. Acta 85 (1964) 103–116. [PMID: 14159288]
[EC created 1961, deleted 1972, reinstated 1976, modified 1983, modified 1999]
Accepted name: cysteine lyase
Reaction: L-cysteine + sulfite = L-cysteate + hydrogen sulfide
Other name(s): cysteine (sulfite) lyase; L-cysteine hydrogen-sulfide-lyase (adding sulfite)
Systematic name: L-cysteine hydrogen-sulfide-lyase (adding sulfite; L-cysteate-forming)
Comments: A pyridoxal-phosphate protein. Can use a second molecule of cysteine (producing lanthionine), or other alkyl thiols, as a replacing agent.
1.  Tolosa, E.A., Chepurnova, N.K., Khomutov, R.M. and Severin, E.S. Reactions catalysed by cysteine lyase from the yolk sac of chicken embryo. Biochim. Biophys. Acta 171 (1969) 369–371. [PMID: 5813025]
[EC created 1972]
Accepted name: L-cysteate sulfo-lyase
Reaction: L-cysteate + H2O = hydrogensulfite + pyruvate + NH3 (overall reaction)
(1a) L-cysteate = hydrogensulfite + 2-aminoprop-2-enoate
(1b) 2-aminoprop-2-enoate = 2-iminopropanoate (spontaneous)
(1c) 2-iminopropanoate + H2O = pyruvate + NH3 (spontaneous)
Glossary: L-cysteate = (2S)-2-amino-3-sulfopropanoate
Other name(s): L-cysteate sulfo-lyase (deaminating); CuyA; L-cysteate bisulfite-lyase (deaminating; pyruvate-forming)
Systematic name: L-cysteate hydrogensulfite-lyase (deaminating; pyruvate-forming)
Comments: A pyridoxal-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing hydrogensulfite 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. D-Cysteine can also act as a substrate, but more slowly. It is converted into hydrogen sulfide, pyruvate, and ammonia. This inducible enzyme from the marine bacterium Silicibacter pomeroyi DSS-3 forms part of the cysteate-degradation pathway.
1.  Denger, K., Smits, T.H.M. and Cook, A.M. L-Cysteate sulpho-lyase, a widespread pyridoxal 5′-phosphate-coupled desulphonative enzyme purified from Silicibacter pomeroyi DSS-3(T). Biochem. J. 394 (2006) 657–664. [PMID: 16302849]
[EC created 2006]