Overview for MACiE Entry M0304
EC Number: 18.104.22.168 (A member of the Oxidoreductases, Acting on the CH-NH2 group of donors, With NAD+ or NADP+ as acceptor)
Enzyme Name: glutamate synthase (NADPH)
Biological Species: Azospirillum brasilense (Bacteria)
Catalytic Chain UniprotKB Accession Codes:
- Q05755 - Glutamate synthase [NADPH] large chain
Representative PDB Code: 1ea0 - ALPHA SUBUNIT OF A. BRASILENSE GLUTAMATE SYNTHASE (Resolution = 3.0 Å).
Catalytic CATH Codes:
- 22.214.171.124 - Glutamine Phosphoribosylpyrophosphate, subunit 1, domain 1
"Other" CATH Codes:
Display structure information
This reaction is irreversible.
Overall Comment: Glutamine hydrolysis is absent (or negligible) in the absence of the other substrates. The enzyme also catalyses the oxidation of NADPH, the ammonia-dependent synthesis of glutamate from 2-oxoglutarate and ammonia and the oxidation of L-glutamate in the presence of iodonitrotetrazolium salts, the latter two of which only occur at high pH. There is still much to be determined with respect to the mechanism of this enzyme  as well as how the cross-control of the synthase and glutaminase activities occurs with such precision. This enzyme utilises three iron-sulfur clusters (two Fe4S4 and one Fe3S4) as well as FMN and FAD as cofactors.
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Stepwise Description of the Reaction
|Step 1||NADP reduces the FAD cofactor.|
|Step 2||A single electron is transferred from FAD, via the iron-sulfur clusters and Met479 to the FMN cofactor.|
|Step 3||A second single electron is transferred from FAD, via the iron-sulfur clusters and Met479 to the FMN cofactor.|
|Step 4||The N-terminus of Cys1 deprotonates water, which deprotonates the thiol group of Cys1, initiating a nucleophilic attack on the amide carbon in an addition reaction.|
|Step 5||The oxyanion initiates an elimination that cleaves ammonia from the bound L-glutamine substrate. Ammonia deprotonates water, which deprotonates the N-terminus of Cys1.|
|Step 6||The N-terminus of Cys1 deprotonates water, which initiates a nucleophilic attack on the carbonyl carbon of the covalently bound intermediate in an addition reaction.|
|Step 7||The oxyanion initiates an elimination that cleaves the C-S bond, the thiolate of Cys1 deprotonates water, which deprotonates the N-terminus of Cys1.|
|Step 8||Ammonia initiates a nucleophilic attack on the C2 of 2-oxoglutarate in an addition reaction.|
|Step 9||Water is produced through an intramolecular elimination forming the 2-iminoglutarate intermediate.|
|Step 10||FMN donates a hydride to the 2-iminoglutarate intermediate.|
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Catalytic Residues Involved
||Location of Function
Main Chain N Terminus
||Main Chain Amide
Organic Cofactors for M0304
Metal Cofactors for M0304
- C. Binda et al. (2000), Structure, 8, 1299-1308. Cross-talk and ammonia channeling between active centers in the unexpected domain arrangement of glutamate synthase.
- M. A. Vanoni et al. (2008), IUBMB Life, 60, 287-300. Structure-function studies of glutamate synthases: a class of self-regulated iron-sulfur flavoenzymes essential for nitrogen assimilation.
- S. Ravasio et al. (2001), Biochemistry, 40, 5533-5541. Determination of the midpoint potential of the FAD and FMN flavin cofactors and of the 3Fe-4S cluster of glutamate synthase.
- R. H. van den Heuvel et al. (2003), J. Mol. Biol., 330, 113-128. The active conformation of glutamate synthase and its binding to ferredoxin.
Homologue information for M0304 (1ea0)
MACiE Homologues (within the PDB)
MACiE Homologues (within UniprotKB/SwissProt)
Entries with at least one Catalytic CATH code in common (different mechanisms):
|M0111 ||glutamate synthase (ferredoxin) |
|M0214 ||amidophosphoribosyltransferase |
|M0082 ||glutamine-fructose-6-phosphate transaminase (isomerizing) |
|M0177 ||proteasome endopeptidase complex |
|M0302 ||asparagine synthase (glutamine-hydrolysing) |
View a comparison of the other reactions in MACiE with the CATH domain 126.96.36.199
View a comparison of the other reactions in MACiE with the CATH domain 188.8.131.52
Links to this entry in other databases