Why does Escherichia coli have two primary pathways for synthesis of glutamate?

Helling, Robert B.

doi:10.1128/jb.176.15.4664-4668.1994

Cited by 111 publications

(134 citation statements)

References 33 publications

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“…GOGAT can fix ammonium into organic molecules (glutamine, thence glutamate and other compounds) when the external concentration of ammonium is low, and it reduces the concentration of glutamine when that concentration becomes high (Reitzer 1986). Note also that a strain deficient in glutamate dehydrogenase has no observable growth phenotype under usual growth conditions (Reitzer 1986) but that GDH appears to be important during energy-limited growth because, through its use, the cost of biosynthesis is scaled down (Helling 1994). …”

Section: Ammonia Assimilation Pathway In E Colimentioning

confidence: 99%

Insights on the Evolution of Metabolic Networks of Unicellular Translationally Biased Organisms from Transcriptomic Data and Sequence Analysis

Carbone

Madden

2005

J Mol Evol

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Abstract. Codon bias is related to metabolic functions in translationally biased organisms, and two facts are argued about. First, genes with high codon bias describe in meaningful ways the metabolic characteristics of the organism; important metabolic pathways corresponding to crucial characteristics of the lifestyle of an organism, such as photosynthesis, nitrification, anaerobic versus aerobic respiration, sulfate reduction, methanogenesis, and others, happen to involve especially biased genes. Second, gene transcriptional levels of sets of experiments representing a significant variation of biological conditions strikingly confirm, in the case of Saccharomyces cerevisiae, that metabolic preferences are detectable by purely statistical analysis: the high metabolic activity of yeast during fermentation is encoded in the high bias of enzymes involved in the associated pathways, suggesting that this genome was affected by a strong evolutionary pressure that favored a predominantly fermentative metabolism of yeast in the wild. The ensemble of metabolic pathways involving enzymes with high codon bias is rather well defined and remains consistent across many species, even those that have not been considered as translationally biased, such as Helicobacter pylori, for instance, reveal some weak form of translational bias for this genome. We provide numerical evidence, supported by experimental data, of these facts and conclude that the metabolic networks of translationally biased genomes, observable today as projections of eons of evolutionary pressure, can be analyzed numerically and predictions of the role of specific pathways during evolution can be derived. The new concepts of Comparative Pathway Index, used to compare organisms with respect to their metabolic networks, and Evolutionary Pathway Index, used to detect evolutionarily meaningful bias in the genetic code from transcriptional data, are introduced.

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Section: Ammonia Assimilation Pathway In E Colimentioning

confidence: 99%

Insights on the Evolution of Metabolic Networks of Unicellular Translationally Biased Organisms from Transcriptomic Data and Sequence Analysis

Carbone

Madden

2005

J Mol Evol

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“…Importantly, parallel metabolic pathways could evolve not only to metabolize qualitatively different nutrient molecules, but also in response to variation in the quantitative availability of nutrients. For example, E. coli has two pathways of glutamate synthesis, one of which can fix ammonium into organic molecules when the external concentration of ammonium is low, while the other plays an important role when the cell is limited for energy, but is not under ammonium restriction (Helling, 1994). Finally, the evolutionary maintenance of compensating isoenzymes in metabolic networks could be explained by selection to increase gene dosage (i.e., to increase flux) (Conant and Wolfe, 2007;Papp et al, 2004), filter nongenetic noise (Kafri et al, 2006), or provide differential regulation of isoforms (Ihmels et al, 2004).…”

Section: Robustness Against Gene Deletions Appears To Be a By-productmentioning

confidence: 99%

A critical view of metabolic network adaptations

2009

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“…The expenditure of NADH, ATP and 2-oxoglutarate in this process (Helling, 1994) would drive the utilization/oxidation of succinate and glucose-carbon. It has been shown that optimization of energy flow requires the functioning of energy-dissipating reactions such as the cycling of glutamine (Stucki, 1980;Tempest, 1978 ;Mora, 1990; Fig.…”

Section: Discussionmentioning

confidence: 99%

Glutamine biosynthesis and the utilization of succinate and glutamine by Rhizobium etli and Sinorhizobium meliloti

Encarnación¹,

Calderón

Gelbard

et al. 1998

Microbiology

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Sinorhizobium meliloti 1021 and Rhizobium etli CE3 turn over nitrogen and carbon from glutamine to ammonium and CO2, respectively. Some of the ammonium released is assimilated back into glutamine, indicating that a glutamine cycle similar to that in Neurospora operates in Rhizobium. In addition, a previously unrecognized metabolic pathway in Rhizobium was discovered - namely, conversion of glutamine-carbon to γ-hydroxybutyric acid and β-hydroxybutyric acid. Additionally, some of the 2-oxoglutarate derived from glutamine catabolism in Rhizobium is converted to succinate in glutamine-containing medium. Both S. meliloti 1021 and R. etli CE3 oxidize succinate preferentially over glutamine when provided with both carbon sources. In contrast to Sinorhizobium meliloti 1021 and Rhizobium etli CE3, an S. meliloti double mutant that lacks both glutamine synthetase (GS) I and II preferentially oxidizes glutamine over succinate when supplied with both substrates. GSII activity is induced in wild-type S. meliloti 1021 and R. etli CE3 grown in succinate-glutamine medium, and this enzyme participates in the cycling of glutamine-carbon and -nitrogen. On the other hand, GSII activity is repressed in both micro-organisms when glutamine is the only carbon source. These findings show that, in medium containing both glutamine and succinate, glutamine synthesis helps drive the utilization of succinate. When glutamine is in excess as an energy-providing substrate its synthesis is restricted, allowing for more effective utilization of glutamine as an energy source.

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Why does Escherichia coli have two primary pathways for synthesis of glutamate?

Cited by 111 publications

References 33 publications

Insights on the Evolution of Metabolic Networks of Unicellular Translationally Biased Organisms from Transcriptomic Data and Sequence Analysis

Insights on the Evolution of Metabolic Networks of Unicellular Translationally Biased Organisms from Transcriptomic Data and Sequence Analysis

A critical view of metabolic network adaptations

Glutamine biosynthesis and the utilization of succinate and glutamine by Rhizobium etli and Sinorhizobium meliloti

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