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Glutamine synthetase,
beta-Grasp domain
Glutamine synthetase.PNG
Crystallographic structure of glutamine synthetase from salmonella typhimurium.[1]
Symbol Gln-synt_N
Pfam PF03951
InterPro IPR008147
SCOP 2gls
Glutamine synthetase,
catalytic domain
Symbol Gln-synt_C
Pfam PF00120
InterPro IPR008146
SCOP 2gls
glutamate-ammonia ligase (glutamine synthetase)
Symbol GLUL
Alt. symbols GLNS
Entrez 2752
HUGO 4341
OMIM 138290
PDB 2qc8
RefSeq NM_002065
UniProt P15104
Other data
EC number
Locus Chr. 1 q31

Glutamine synthetase (GS) (EC[2] is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Glutamate + ATP + NH3 → Glutamine + ADP + phosphate + H2O



There seem to be three different classes of GS:[3][4][5]

  • Class I enzymes (GSI) are specific to prokaryotes, and are oligomers of 12 identical subunits.[6] The activity of GSI-type enzyme is controlled by the adenylation of a tyrosine residue. The adenylated enzyme is inactive [7].

Plants have two or more isozymes of GSII, one of the isozymes is translocated into the chloroplast.

  • Class III enzymes (GSIII) has, currently, only been found in Bacteroides fragilis and in Butyrivibrio fibrisolvens. It is a hexamer of identical chains. It is much larger (about 700 amino acids) than the GSI (450 to 470 amino acids) or GSII (350 to 420 amino acids) enzymes.

While the three classes of GS's are clearly structurally related, the sequence similarities are not so extensive.



  1. ^ a b Gill HS, Eisenberg D (February 2001). "The crystal structure of phosphinothricin in the active site of glutamine synthetase illuminates the mechanism of enzymatic inhibition". Biochemistry 40 (7): 1903–12. doi:10.1021/bi002438h. PMID 11329256.  
  2. ^ Eisenberg D, Almassy RJ, Janson CA, Chapman MS, Suh SW, Cascio D, Smith WW (1987). "Some evolutionary relationships of the primary biological catalysts glutamine synthetase and RuBisCO". Cold Spring Harb. Symp. Quant. Biol. 52: 483–90. PMID 2900091.  
  3. ^ Kumada Y, Benson DR, Hillemann D, Hosted TJ, Rochefort DA, Thompson CJ, Wohlleben W, Tateno Y (April 1993). "Evolution of the glutamine synthetase gene, one of the oldest existing and functioning genes". Proc. Natl. Acad. Sci. U.S.A. 90 (7): 3009–13. PMID 8096645.  
  4. ^ Shatters RG, Kahn ML (November 1989). "Glutamine synthetase II in Rhizobium: reexamination of the proposed horizontal transfer of DNA from eukaryotes to prokaryotes". J. Mol. Evol. 29 (5): 422–8. PMID 2575672.  
  5. ^ Brown JR, Masuchi Y, Robb FT, Doolittle WF (June 1994). "Evolutionary relationships of bacterial and archaeal glutamine synthetase genes". J. Mol. Evol. 38 (6): 566–76. PMID 7916055.  
  6. ^ "GSI structure". Retrieved 2009-03-31.  
  7. ^ InterPro:IPR001637 Glutamine synthetase class-I, adenylation site
  8. ^ PDB 2OJW; Krajewski WW, Collins R, Holmberg-Schiavone L, Jones TA, Karlberg T, Mowbray SL (January 2008). "Crystal structures of mammalian glutamine synthetases illustrate substrate-induced conformational changes and provide opportunities for drug and herbicide design". J. Mol. Biol. 375 (1): 217–28. doi:10.1016/j.jmb.2007.10.029. PMID 18005987.  

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