ExplorEnz: EC 4.2.1.20

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4.2.1.20

Accepted name:

tryptophan synthase

Reaction:

L-serine + 1-C-(indol-3-yl)glycerol 3-phosphate = L-tryptophan + D-glyceraldehyde 3-phosphate + H₂O (overall reaction)
(1a) 1-C-(indol-3-yl)glycerol 3-phosphate = indole + D-glyceraldehyde 3-phosphate
(1b) L-serine + indole = L-tryptophan + H₂O

For diagram of tryptophan biosynthesis, click here

Other name(s):

L-tryptophan synthetase; indoleglycerol phosphate aldolase; tryptophan desmolase; tryptophan synthetase; L-serine hydro-lyase (adding indoleglycerol-phosphate); L-serine hydro-lyase [adding 1-C-(indol-3-yl)glycerol 3-phosphate, L-tryptophan and glyceraldehyde-3-phosphate-forming]

Systematic name:

L-serine hydro-lyase [adding 1-C-(indol-3-yl)glycerol 3-phosphate, L-tryptophan and D-glyceraldehyde-3-phosphate-forming]

Comments:

A pyridoxal-phosphate protein. The α-subunit catalyses the conversion of 1-C-(indol-3-yl)glycerol 3-phosphate to indole and D-glyceraldehyde 3-phosphate (this reaction was included formerly under EC 4.1.2.8). The indole migrates to the β-subunit where, in the presence of pyridoxal 5′-phosphate, it is combined with L-serine to form L-tryptophan. In some organisms this enzyme is part of a multifunctional protein that also includes one or more of the enzymes EC 2.4.2.18 (anthranilate phosphoribosyltransferase), EC 4.1.1.48 (indole-3-glycerol-phosphate synthase), EC 4.1.3.27 (anthranilate synthase) and EC 5.3.1.24 (phosphoribosylanthranilate isomerase). In thermophilic organisms, where the high temperature enhances diffusion and causes the loss of indole, a protein similar to the β subunit can be found (EC 4.2.1.122). That enzyme cannot combine with the α unit of EC 4.2.1.20 to form a complex.

Links to other databases:

BRENDA, EXPASY, Gene, GTD, KEGG, MetaCyc, PDB, CAS registry number: 9014-52-2

References:

1.	Crawford, I.P. and Yanofsky, C. On the separation of the tryptophan synthetase of Escherichia coli into two protein components. Proc. Natl. Acad. Sci. USA 44 (1958) 1161–1170. [DOI] [PMID: 16590328]
2.	Creighton, T.E. and Yanofsky, C. Chorismate to tryptophan (Escherichia coli) - anthranilate synthetase, PR transferase, PRA isomerase, InGP synthetase, tryptophan synthetase. Methods Enzymol. 17A (1970) 365–380.
3.	Hütter, R., Niederberger, P. and DeMoss, J.A. Tryptophan synthetic genes in eukaryotic microorganisms. Annu. Rev. Microbiol. 40 (1986) 55–77. [DOI] [PMID: 3535653]
4.	Hyde, C.C., Ahmed, S.A., Padlan, E.A., Miles, E.W. and Davies, D.R. Three-dimensional structure of the tryptophan synthase α2β2 multienzyme complex from Salmonella typhimurium. J. Biol. Chem. 263 (1988) 17857–17871. [PMID: 3053720]
5.	Woehl, E. and Dunn, M.F. Mechanisms of monovalent cation action in enzyme catalysis: the tryptophan synthase α-, β-, and αβ-reactions. Biochemistry 38 (1999) 7131–7141. [DOI] [PMID: 10353823]

[EC 4.2.1.20 created 1961, modified 1976, modified 2002, modified 2011]