If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Biosynthesis → Amino Acids Biosynthesis → Proteinogenic Amino Acids Biosynthesis → L-glutamate Biosynthesis|
There are two pathways by which E. coli synthesizes glutamate from ammonia. If complex sources of nitrogen are available, still other pathways (see below) become available and take over glutamate synthesis. The pathway shown here is one of the steps in one of the pathways by which glutamate is synthesized from ammonia. The other step (L-glutamine biosynthesis I) in this pathway is the synthesis of glutamine from ammonia. Then in the step shown here that amido group is transferred to α-ketoglutarate yielding glutamate. Because glutamine biosynthesis utilizes glutamate and the reaction shown here yields 2 molecules of glutamate, these two reactions function as a cycle (see ammonia assimilation cycle III), each turn of which produces one molecule of glutamate at the expense of one molecule each of ammonia, ATP, NADPH, and α-ketoglutarate. The other ammonia-to-glutamate pathway, the one catalyzed by glutamate dehydrogenase (L-glutamate biosynthesis III), also utilizes NADPH, and α-ketoglutarate, but it does not require ATP to drive the reaction. The Km for ammonia in this reaction is much higher than the Km for ammonia in ATP-driven cyclic pathway.
The two ammonia-to-glutamate pathways are regulated so as to operate under different environmental circumstances. The ATP-independent pathway functions when ammonia is abundant; the ATP-driven pathway functions when concentrations of ammonia are low. The ATP-independent pathway offers significant energy savings because when functioning, the ATP-driven pathway utilizes over 10 percent of the cell's total expenditure of ATP.
If complex sources of nitrogen are available, glutamate can be synthesized from arginine (L-arginine degradation II (AST pathway)) or proline (proline degradation) or from α-ketoglutarate by transamination of the amino group from arginine or aspartate.
The complexity of glutamate biosynthesis reflects the quantitatively central role that this amino acid plays in the metabolism of E. coli. It is a major constituent of E. coli's proteins and because it is a major nitrogen donor for other biosyntheses, about 80% of the cell's nitrogen flows through glutamate when E. coli is growing on a medium containing ammonia as the total source of nitrogen.
Review: Reitzer, L. (2004) "Biosynthesis of Glutamate, Aspartate, Asparagine, L -Alanine, and D -Alanine." EcoSal 22.214.171.124 [ECOSAL]
Superpathways: ammonia assimilation cycle III
Variants: L-glutamate biosynthesis III
Arifuzzaman06: Arifuzzaman M, Maeda M, Itoh A, Nishikata K, Takita C, Saito R, Ara T, Nakahigashi K, Huang HC, Hirai A, Tsuzuki K, Nakamura S, Altaf-Ul-Amin M, Oshima T, Baba T, Yamamoto N, Kawamura T, Ioka-Nakamichi T, Kitagawa M, Tomita M, Kanaya S, Wada C, Mori H (2006). "Large-scale identification of protein-protein interaction of Escherichia coli K-12." Genome Res 16(5);686-91. PMID: 16606699
Butland05: Butland G, Peregrin-Alvarez JM, Li J, Yang W, Yang X, Canadien V, Starostine A, Richards D, Beattie B, Krogan N, Davey M, Parkinson J, Greenblatt J, Emili A (2005). "Interaction network containing conserved and essential protein complexes in Escherichia coli." Nature 433(7025);531-7. PMID: 15690043
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Goss01: Goss TJ, Perez-Matos A, Bender RA (2001). "Roles of glutamate synthase, gltBD, and gltF in nitrogen metabolism of Escherichia coli and Klebsiella aerogenes." J Bacteriol 183(22);6607-19. PMID: 11673431
Lapointe75: Lapointe J, Delcuve G, Duplain L (1975). "Derepressed levels of glutamate synthase and glutamine synthetase in Escherichia coli mutants altered in glutamyl-transfer ribonucleic acid synthetase." J Bacteriol 123(3);843-50. PMID: 239924
Lozoya80: Lozoya E, Sanchez-Pescador R, Covarrubias A, Vichido I, Bolivar F (1980). "Tight linkage of genes that encode the two glutamate synthase subunits of Escherichia coli K-12." J Bacteriol 144(2);616-21. PMID: 6107287
Metcalf90: Metcalf WW, Steed PM, Wanner BL (1990). "Identification of phosphate starvation-inducible genes in Escherichia coli K-12 by DNA sequence analysis of psi::lacZ(Mu d1) transcriptional fusions." J Bacteriol 172(6);3191-200. PMID: 2160940
Saroja96: Saroja GN, Gowrishankar J (1996). "Roles of SpoT and FNR in NH4+ assimilation and osmoregulation in GOGAT (glutamate synthase)-deficient mutants of Escherichia coli." J Bacteriol 178(14);4105-14. PMID: 8763938
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