Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A mutant of Klebsiella aerogenes lacking glutamate synthase activity (asm-200) is blocked in only one pathway of glutamate synthesis and can still use glutamate dehydrogenase to produce glutamate when ammonia in sufficient concentration, i.e., higher than 1 mM, is provided in the medium. However, a mutant that has neither glutamate synthase nor glutamate dehydrogenase activities (asm-200, gdhD1) requires glutamate. Transductants obtained by phage grown on wild-type cells of this double mutant, selected on medium containing less than 1 mM ammonia, regain glutamate synthase but not glutamate dehydrogenase. Surprisingly, these gdhD1 transductants grow as well in a variety of media as does a strain with glutamate dehydrogenase activity. Furthermore, transductions with these and other mutants indicate that the genes encoding glutamate synthase, glutamate dehydrogenase, glutamine synthetase, and citrate synthase are not closely linked.
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PMID:Mutants of Klebsiella aerogenes lacking glutamate dehydrogenase. 414 14

Strain SF22, a glutamine-requiring (Gln-) mutant of Bacillus subtilis SMY, is likely to have a mutation in the structural gene for glutamine synthetase, since this strain synthesized 22 to 55% as much glutamine synthetase antigen as did wild-type cells in a 10-min period but had less than 3% of wild-type glutamine synthetase enzymatic activity. The expression of several genes subject to glucose catabolite repression was altered in the Gln- mutant. The induced levels of alpha-glucosidase, histidase, and aconitase were 3.5- to 4-fold higher in SF22 cells than in wild-type cells grown in glucose-glutamine medium, and citrate synthase levels were 8-fold higher in the Gln- mutant than in wild-type cells. The relief of glucose catabolite repression in the Gln- mutant may result from poor utilization of glucose. Examination of the intracellular metabolite pools of cells grown in glucose-glutamine medium showed that the glucose-6-phosphate pool was 2.5-fold lower, the pyruvate pool was 4-fold lower, and the 2-ketoglutarate pool was 2.5-fold lower in the Gln- cells than they were in wild-type cells. Intracellular levels of glutamine were sixfold higher in the Gln- mutant than in wild-type cells. Measurements of enzymes involved in glutamine transport and utilization showed that the elevated pools of glutamine in the Gln- mutant resulted from a threefold increase in glutamine permease and a fivefold decrease in glutamate synthase. The pleiotropic effect of the gln-22 mutation on the expression of several genes suggests that either the glutamine synthetase protein or its enzymatic product, glutamine, is involved in the regulation of several metabolic pathways in B. subtilis.
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PMID:Bacillus subtilis glutamine synthetase mutants pleiotropically altered in glucose catabolite repression. 614 Nov 56

Mitochondrial NAD-dependent (IDH) and cytosolic NADP-dependent isocitrate dehydrogenases have been considered as candidates for the production of 2-oxoglutarate required by the glutamine synthetase/glutamate synthase cycle. The increase in IDH transcripts in leaf and root tissues, induced by nitrate or NH4+ resupply to short-term N-starved tobacco (Nicotiana tabacum) plants, suggested that this enzyme could play such a role. The leaf and root steady-state mRNA levels of citrate synthase, acotinase, IDH, and glutamine synthetase were found to respond similarly to nitrate, whereas those for cytosolic NADP-dependent isocitrate dehydrogenase and fumarase responded differently. This apparent coordination occurred only at the mRNA level, since activity and protein levels of certain corresponding enzymes were not altered. Roots and leaves were not affected to the same extent either by N starvation or nitrate addition, the roots showing smaller changes in N metabolite levels. After nitrate resupply, these organs showed different response kinetics with respect to mRNA and N metabolite levels, suggesting that under such conditions nitrate assimilation was preferentially carried out in the roots. The differential effects appeared to reflect the C/N status after N starvation, the response kinetics being associated with the nitrate assimilatory capacity of each organ, signaled either by nitrate status or by metabolite(s) associated with its metabolism.
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PMID:Simultaneous expression of NAD-dependent isocitrate dehydrogenase and other krebs cycle genes after nitrate resupply to short-term nitrogen-starved tobacco 1039 6

Nia30(145) transformants with very low nitrate reductase activity provide an in vivo screen to identify processes that are regulated by nitrate. Nia30(145) resembles nitrate-limited wild-type plants with respect to growth rate and protein and amino acid content but accumulates large amounts of nitrate when it is grown on high nitrate. The transcripts for nitrate reductase (NR), nitrite reductase, cytosolic glutamine synthetase, and glutamate synthase increased; NR and nitrite reductase activity increased in leaves and roots; and glutamine synthetase activity increased in roots. The transcripts for phosphoenolpyruvate carboxylase, cytosolic pyruvate kinase, citrate synthase, and NADP-isocitrate dehydrogenase increased; phosphoenolpyruvate carboxylase activity increased; and malate, citrate, isocitrate, and [alpha]-oxoglutarate accumulated in leaves and roots. There was a decrease of the ADP-glucose pyrophosphorylase transcript and activity, and starch decreased in the leaves and roots. After adding 12 mM nitrate to nitrate-limited Nia30(145), the transcripts for NR and phosphoenolpyruvate carboxylase increased, and the transcripts for ADP-glucose pyrophosphorylase decreased within 2 and 4 hr, respectively. Starch was remobilized at almost the same rate as in wild-type plants, even though growth was not stimulated in Nia30(145). It is proposed that nitrate acts as a signal to initiate coordinated changes in carbon and nitrogen metabolism.
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PMID:Nitrate Acts as a Signal to Induce Organic Acid Metabolism and Repress Starch Metabolism in Tobacco. 1223 66

The utilization of some agro-industrial wastes as soil conditioners to provide free-living nitrogen-fixing bacterial populations (e.g. Azospirillum spp.) with carbon and energy sources, may be an interesting perspective for agriculture. However, the presence of ammonium nitrogen in cultivated soils and/or various wastes could inhibit the growth of the nitrogen-fixing populations. The present investigation shows that growth of Azospirillum lipoferum was restricted at a dissolved oxygen (DO) concentration equal to 135 microM, when the initial NH4Cl concentration increased from 0.5 to 0.9 g/l. The activities of both citrate synthase (CS) and isocitrate dehydrogenase were significantly decreased in the presence of 0.9 g/l NH4Cl (e.g., 40% and 66%, respectively, in cells incubated for 95 h), while ammonium assimilation occurred via the glutamate dehydrogenase reaction. Furthermore, growth limitation occurred even in the presence of 0.5 g/l NH4Cl, when the DO concentration decreased from 135 to 30 microM. The activities of both CS and succinate dehydrogenase were dramatically decreased in cells grown at the lower DO concentration (e.g., 90% and 93% respectively, in a 95 h incubation), while ammonium assimilation was limited due to the low activities of both glutamate dehydrogenase and glutamate synthase. It is concluded that the threshold of ammonium concentration at which growth of A. lipoferum is limited, depends on the DO concentration in the medium.
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PMID:Metabolic activities in Azospirillum lipoferum grown in the presence of NH4+. 1276 47

The effects through which an alfalfa protein hydrolysate (EM) possessing gibberellin- and auxin-like activity may promote plant nitrogen (N) nutrition have been investigated in Zea mays L. Treatment with 0.01 or 0.1 mg L(-1) EM for 48 h resulted in enhanced plant growth and leaf sugar accumulation. Concomitantly, the level of nitrates decreased, whereas total N percentage was unchanged. The activity of a number of enzymes involved in carbon (C) metabolism (malate dehydrogenase, MDH; isocitrate dehydrogenase, IDH; citrate synthase, CS) and N reduction and assimilation (nitrate reductase, NR; nitrite reductase, NiR; glutamine synthetase, GS; glutamate synthase, GOGAT; aspartate aminotransferase, AspAT) was significantly induced by EM supply to plants, and the transcription pattern of MDH, IDH, CS, and NR strongly correlated with data of enzyme activity. The transcript accumulation of asparagine synthetase (AS) was also induced by EM in the roots. The results suggest that EM might promote nitrogen assimilation in plants through a coordinate regulation of C and N metabolic pathways and open the way for further research on protein hydrolysates as a valid tool to improve N use efficiency and, as a consequence, to reduce the intensive use of inorganic N fertilizers in agriculture.
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PMID:Effects of an alfalfa protein hydrolysate on the gene expression and activity of enzymes of the tricarboxylic acid (TCA) cycle and nitrogen metabolism in Zea mays L. 1905 64

Microalgae are a promising feedstock for biofuel production. Microalgal metabolic pathways are heavily influenced by environmental factors. For instance, lipid metabolism can be induced by nitrogen-limiting conditions. However, the underlying mechanisms of lipid biosynthesis are unclear. In this study, we analyzed the global metabolic profiles of three genetically closely related Chlorella strains (C1, C2, and C3) with significant differences in lipid productivity to identify the contributions of key metabolic pathways to lipid metabolism. We found that nitrogen obtained from amino acid catabolism was assimilated via the glutamate-glutamine pathway and then stored as amino acids and intermediate molecules (particularly proline, alanine, arginine, succinate, and gamma-aminobutyrate) via the corresponding metabolic pathways, which led to carbon-nitrogen disequilibrium. Excess carbon obtained from photosynthesis or glycolysis was re-distributed into carbon-containing compounds, such as glucose-6-phosphate, fructose-6-phosphate, phosphoenolpyruvate, lactate, citrate, 3-hydroxybutyrate, and leucine, and then diverted into lipid metabolism for the production of storage lipids via the gamma-aminobutyrate pathway, glycolysis, and the tricarboxylic acid cycle. These results were substantiated in the model green alga Chlamydomonas reinhardtii by analyzing various mutants deficient in glutamate synthase/NADH-dependent, glutamate synthase/Fd-dependent, glutamine synthetase, aspartate aminotransferase, alanine aminotransferase, pyruvate kinase, and citrate synthase. Our study suggests that not only carbon but also nitrogen assimilation and distribution pathways contribute to lipid biosynthesis. Furthermore, these findings may facilitate genetic engineering efforts to enhance microalgal biofuel production.
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PMID:Comparative metabolic profiling of the lipid-producing green microalga Chlorella reveals that nitrogen and carbon metabolic pathways contribute to lipid metabolism. 2863 Jun 48