Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An important biochemical feature of autotrophs, land plants and algae, is their incorporation of inorganic nitrogen, nitrate and ammonium, into the carbon skeleton. Nitrate and ammonium are converted into glutamine and glutamate to produce organic nitrogen compounds, for example proteins and nucleic acids. Ammonium is not only a preferred nitrogen source but also a key metabolite, situated at the junction between carbon metabolism and nitrogen assimilation, because nitrogen compounds can choose an alternative pathway according to the stages of their growth and environmental conditions. The enzymes involved in the reactions are nitrate reductase (EC 1.6.6.1-2), nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.13-14, 1.4.7.1), glutamate dehydrogenase (EC 1.4.1.2-4), aspartate aminotransferase (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Many of these enzymes exist in multiple forms in different subcellular compartments within different organs and tissues, and play sometimes overlapping and sometimes distinctive roles. Here, we summarize the biochemical characteristics and the physiological roles of these enzymes. We also analyse the molecular evolution of glutamine synthetase, glutamate synthase and glutamate dehydrogenase, and discuss the evolutionary relationships of these three enzymes.
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PMID:Nitrogen-assimilating enzymes in land plants and algae: phylogenic and physiological perspectives. 1220 56

Density gradient separation of plastids from leaf and root tissue was carried out. The distribution in the gradients of the activity of the following enzymes was determined: nitrite reductase, glutamine synthetase, acetolactate synthetase, aspartate aminotransferase, catalase, cytochrome oxidase, and triosephosphate isomerase. The distribution of chlorophyll was followed in gradients from leaf tissue. The presence of plastids that have retained their stroma enzymes was denoted by a peak of triosephosphate isomerase activity. Coincidental with this peak were bands of nitrite reductase, acetolactate synthetase, glutamine synthetase, and aspartate aminotransferase activity. The results suggest that most, if not all, the nitrite reductase and acetolactate synthetase activity of the cell is in the plastids. The plastids were found to contain only part of the total glutamine synthetase, aspartate aminotransferase, and triosephosphate dehydrogenase activity in the cell. Some evidence was obtained for low levels of glutamate dehydrogenase activity in chloroplasts.
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PMID:The location of nitrite reductase and other enzymes related to amino Acid biosynthesis in the plastids of root and leaves. 1665 26

In normal conditions, nitric oxide (NO) is oxidized to the anion nitrite, but in hypoxia, this nitrite may be reduced back to NO by the nitrite reductase action of deoxygenated hemoglobin, acidic disproportionation, or xanthine oxidoreductase (XOR). Herein, is investigated the effects of topical sodium nitrite administration in a rat model of renal ischemia/reperfusion (I/R) injury. Rats were subjected to 60 min of bilateral renal ischemia and 6 h of reperfusion in the absence or presence of sodium nitrite (30 nmol) administered topically 1 min before reperfusion. Serum creatinine, serum aspartate aminotransferase, creatinine clearance, fractional excretion of Na(+), and plasma nitrite/nitrate concentrations were measured. The nitrite-derived NO-generating capacity of renal tissue was determined under acidic and hypoxic conditions by ozone chemiluminescence in homogenates of kidneys that were subjected to sham, ischemia-only, and I/R conditions. Nitrite significantly attenuated renal dysfunction and injury, an effect that was abolished by previous treatment of rats with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (2.5 mumol intravenously 5 min before ischemia and 50 nmol topically 6 min before reperfusion). Renal tissue homogenates produced significant amounts of NO from nitrite, an effect that was attenuated significantly by the xanthine oxidoreductase inhibitor allopurinol. Taken together, these findings demonstrate that topically administered sodium nitrite protects the rat kidney against I/R injury and dysfunction in vivo via the generation, in part, of xanthine oxidoreductase-catalyzed NO production. These observations suggest that nitrite therapy might prove beneficial in protecting kidney function and integrity during periods of I/R such as those encountered in renal transplantation.
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PMID:Nitrite-derived nitric oxide protects the rat kidney against ischemia/reperfusion injury in vivo: role for xanthine oxidoreductase. 1720 21

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

The influences of 50 and 100muM Ni on growth, tissue Ni accumulation, concentrations of nitrate, ammonium, glutamate, and proline as well as the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), alanine aminotransferase (AlaAT), and aspartate aminotransferase (AspAT) were examined in the shoots of wheat seedlings cv. Zyta. Exposure of the seedlings to Ni resulted in a rapid accumulation of this metal in the shoots, which was accompanied by significant reduction in fresh weight of these organs. Tissue nitrate content decreased in response to Ni stress, while ammonium concentration increased substantially. Glutamate concentration was slightly lowered up to the 4th day of the metal exposure. In contrast, proline content increased significantly, starting from the first day after Ni treatment. NR activity showed a decline of up to 40% below the control level after Ni application; however, its activation state remained unaltered. Heavy metal treatment also resulted in a marked decrease in NiR activity, which after 7d of exposure to 100muM Ni was almost 80% lower than in the control. GS activity in wheat shoots was not influenced by Ni application. Contrary to Fd-GOGAT exhibiting reduced activity in the shoots of Ni-treated wheat seedlings, NADH-GOGAT activity was considerably enhanced, exceeding the control value even by 165%. After 7d of exposure to Ni, both NADH-GDH and NAD-GDH activities in wheat shoots were markedly induced; however, NAD-GDH activity showed a significant decrease at the early stage of the experiment. Both AlaAT and AspAT glutamate-producing activities were considerably stimulated by Ni treatment. Our results suggest that induction of NADH-GOGAT, NADH-GDH, AlaAT, and AspAT activities may compensate for the reduced Fd-GOGAT activity and serve as an alternative means of glutamate synthesis in wheat shoots under Ni stress.
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PMID:Nickel-induced changes in nitrogen metabolism in wheat shoots. 1918 88

Hydrogen sulfide (H2S) modulates plant tolerance to abiotic stresses, but its regulatory effects on nitrogen metabolism and chloroplast protection under nickel (Ni) stress in crop plants remain elusive. Taking this into account, we investigated the potential roles of sodium hydrosulfide (NaHS), a H2S generator, in the improvement of growth performance of rice plants under Ni stress. Results showed that NaHS successfully reversed the adverse effects of Ni, as reflected in plant growth and biomass, and photosynthesis attributes including photosynthetic rates, stomatal conductance, transpiration rate, internal CO2 concentration and photosynthetic pigment contents. NaHS generated H2S plays a crucial role in controlling the photosynthetic machinery of rice as evidenced by the ultrastructure of chloroplast viewed under transmission electron microscope (TEM). The reduced content of Ni in roots and leaves of NaHS-supplemented Ni-stressed plants has revealed the restricted uptake and accumulation of Ni. A rescue of NaHS to the Ni-induced decline in nitrate (NO3-) content and the activities NO3- biosynthesizing enzymes nitrate reductase, nitrite reductase, glutamate synthase, glutamate oxaloacetate transaminase, glutamine synthetase, and glutamate pyruvate transaminase in leaves indicated a positive role of H2S on NO3- metabolism in rice under Ni stress. NaHS application also reverted Ni-mediated increases in ammonium (NH4+) content and glutamate dehydrogenase activity, implying H2S-induced alleviation of NH4+ toxicity. The regulatory effects of H2S on nitrogen metabolism was further confirmed by increased and decreased transcript abundance of NO3- and NH4+ metabolism associated genes, respectively. Our study suggests a decisive role of H2S in controlling Ni toxicity as elucidated by the novel findings such as enhanced gas exchanged parameters, Ni homeostasis and chloroplast protection. Moreover, this article highlights the significance of H2S in controlling chloroplast biogenesis and nitrogen metabolism in rice crop under Ni stress.
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PMID:Hydrogen sulfide enhances rice tolerance to nickel through the prevention of chloroplast damage and the improvement of nitrogen metabolism under excessive nickel. 3085 14

Although the nitrate assimilation into amino acids in photosynthetic leaf tissues is active under the light, the studies during 1950s and 1970s in the dark nitrate assimilation provided fragmental and variable activities, and the mechanism of reductant supply to nitrate assimilation in darkness remained unclear. 15N tracing experiments unraveled the assimilatory mechanism of nitrogen from nitrate into amino acids in the light and in darkness by the reactions of nitrate and nitrite reductases, glutamine synthetase, glutamate synthase, aspartate aminotransferase, and asparagine synthetase. Nitrogen assimilation in illuminated leaves and non-photosynthetic roots occurs either in the redundant way or in the specific manner regarding the isoforms of nitrogen assimilatory enzymes in their cellular compartments. The electron supplying systems necessary to the enzymatic reactions share in part a similar electron donor system at the expense of carbohydrates in both leaves and roots, but also distinct reducing systems regarding the reactions of Fd-nitrite reductase and Fd-glutamate synthase in the photosynthetic and non-photosynthetic organs.
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PMID:Light-Independent Nitrogen Assimilation in Plant Leaves: Nitrate Incorporation into Glutamine, Glutamate, Aspartate, and Asparagine Traced by 15N. 3302 8