The Enzyme Database

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Accepted name: imidazole glycerol-phosphate synthase
Reaction: 5-[(5-phospho-1-deoxy-D-ribulos-1-ylamino)methylideneamino]-1-(5-phospho-β-D-ribosyl)imidazole-4-carboxamide + L-glutamine = 5-amino-1-(5-phospho-β-D-ribosyl)imidazole-4-carboxamide + D-erythro-1-(imidazol-4-yl)glycerol 3-phosphate + L-glutamate (overall reaction)
(1a) L-glutamine + H2O = L-glutamate + NH3
(1b) 5-[(5-phospho-1-deoxy-D-ribulos-1-ylamino)methylideneamino]-1-(5-phospho-β-D-ribosyl)imidazole-4-carboxamide + NH3 = 5-amino-1-(5-phospho-β-D-ribosyl)imidazole-4-carboxamide + D-erythro-1-(imidazol-4-yl)glycerol 3-phosphate + H2O
For diagram of histidine biosynthesis (late stages), click here
Other name(s): IGP synthase; hisFH (gene names); HIS7 (gene name)
Systematic name: 5-[(5-phospho-1-deoxy-D-ribulos-1-ylamino)methylideneamino]-1-(5-phospho-β-D-ribosyl)imidazole-4-carboxamide D-erythro-1-(imidazol-4-yl)glycerol 3-phosphate-lyase (L-glutamine-hydrolysing; 5-amino-1-(5-phospho-β-D-ribosyl)imidazole-4-carboxamide-forming)
Comments: The enzyme is involved in histidine biosynthesis, as well as purine nucleotide biosynthesis. The enzymes from archaea and bacteria are heterodimeric. A glutaminase component (cf. EC, glutaminase) produces an ammonia molecule that is transferred by a 25 Å tunnel to a cyclase component, which adds it to the imidazole ring, leading to lysis of the molecule and cyclization of one of the products. The glutminase subunit is only active within the dimeric complex. In fungi and plants the two subunits are combined into a single polypeptide.
Links to other databases: BRENDA, EXPASY, Gene, KEGG, MetaCyc, PDB
1.  Klem, T.J. and Davisson, V.J. Imidazole glycerol phosphate synthase: the glutamine amidotransferase in histidine biosynthesis. Biochemistry 32 (1993) 5177–5186. [PMID: 8494895]
2.  Fujimori, K. and Ohta, D. An Arabidopsis cDNA encoding a bifunctional glutamine amidotransferase/cyclase suppresses the histidine auxotrophy of a Saccharomyces cerevisiae his7 mutant. FEBS Lett. 428 (1998) 229–234. [PMID: 9654139]
3.  Beismann-Driemeyer, S. and Sterner, R. Imidazole glycerol phosphate synthase from Thermotoga maritima. Quaternary structure, steady-state kinetics, and reaction mechanism of the bienzyme complex. J. Biol. Chem. 276 (2001) 20387–20396. [PMID: 11264293]
4.  Douangamath, A., Walker, M., Beismann-Driemeyer, S., Vega-Fernandez, M.C., Sterner, R. and Wilmanns, M. Structural evidence for ammonia tunneling across the (β α)8 barrel of the imidazole glycerol phosphate synthase bienzyme complex. Structure 10 (2002) 185–193. [PMID: 11839304]
5.  Chaudhuri, B.N., Lange, S.C., Myers, R.S., Davisson, V.J. and Smith, J.L. Toward understanding the mechanism of the complex cyclization reaction catalyzed by imidazole glycerolphosphate synthase: crystal structures of a ternary complex and the free enzyme. Biochemistry 42 (2003) 7003–7012. [PMID: 12795595]
[EC created 2018]

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