Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.6.1.1 (aspartate aminotransferase)
21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A comparative assay of nitrogen metabolism enzymes in the Yarrowia lipolytica mutant N1 grown under conditions promoting the overproduction of either alpha-ketoglutaric acid (KGA) or citric acid showed that the overproduction of KGA correlates with an increase in the activities of the NAD- and NADP-linked glutamate dehydrogenase, glutamic-pyruvic transaminase, and glutamic-oxaloacetic transaminase reactions. These reactions are likely to be responsible for the overproduction of KGA by this mutant. In contrast, the overproduction of citric acid correlated with a decline in the activities of the NAD- and NADP-linked glutamate dehydrogenases and with an increase in the activities of glutamine synthetase and glutamate synthase.
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PMID:[Biochemical characterization of the yeast Yarrowia lipolytica overproducing carboxylic acids from ethanol. Nitrogen metabolism enzymes]. 1452 35

BACKGROUND: There are several reports that indicate a linkage between exposure to power frequency (50 - 60 Hz) magnetic fields with abnormalities in the early embryonic development of the chicken. The present study was designed to understand whether power frequency electromagnetic fields could act as an environmental insult and invoke any neurochemical or toxicological changes in developing chick embryo model. METHODS: Fertilized chicken eggs were subjected to continuous exposure to magnetic fields (50 Hz) of varying intensities (5, 50 or 100 microT) for a period of up to 15 days. The embryos were taken out of the eggs on day 5, day 10 and day 15. Neurochemical (norepinephrine and 5-hydroxytryptamine) and amino acid (tyrosine, glutamine and tryptophan) contents were measured, along with an assay of the enzyme glutamine synthetase in the brain. Preliminary toxicological investigations were carried out based on aminotransferases (AST and ALT) and lactate dehydrogenase activities in the whole embryo as well as in the liver. RESULTS: The study revealed that there was a significant increase (p < 0.01 and p < 0.001) in the level of norepinephrine accompanied by a significant decrease (p < 0.01 and p < 0.001) in the tyrosine content in the brain on day 15 following exposure to 5, 50 and 100 microT magnetic fields. There was a significant increase (p < 0.001) in glutamine synthetase activity resulting in the significantly enhanced (p < 0.001) level of glutamine in the brain on day 15 (for 100 microT only). The possible mechanisms for these alterations are discussed. Further, magnetic fields had no effect on the levels of tryptophan and 5-hydroxytryptamine in the brain. Similarly, there was no effect on the activity of either aminotransferases or lactate dehydrogenase in the whole embryo or liver due to magnetic field exposure. CONCLUSIONS: Based on these studies we conclude that magnetic field-induced changes in norepinephrine levels might help explain alterations in the circadian rhythm, observed during magnetic field stress. Also, the enhanced level of glutamine can act as a contributing factor for developmental abnormalities.
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PMID:Biological effects of power frequency magnetic fields: Neurochemical and toxicological changes in developing chick embryos. 1475 60

Nitrogen assimilation is a vital process controlling plant growth and development. Inorganic nitrogen is assimilated into the amino acids glutamine, glutamate, asparagine, and aspartate, which serve as important nitrogen carriers in plants. The enzymes glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), aspartate aminotransferase (AspAT), and asparagine synthetase (AS) are responsible for the biosynthesis of these nitrogen-carrying amino acids. Biochemical studies have revealed the existence of multiple isoenzymes for each of these enzymes. Recent molecular analyses demonstrate that each enzyme is encoded by a gene family wherein individual members encode distinct isoenzymes that are differentially regulated by environmental stimuli, metabolic control, developmental control, and tissue/cell-type specificity. We review the recent progress in using molecular-genetic approaches to delineate the regulatory mechanisms controlling nitrogen assimilation into amino acids and to define the physiological role of each isoenzyme involved in this metabolic pathway.
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PMID:THE MOLECULAR-GENETICS OF NITROGEN ASSIMILATION INTO AMINO ACIDS IN HIGHER PLANTS. 1501 1

Changes in oxygen and/or glucose availability may result in altered levels of ATP production and amino acid levels, and alteration in lactic acid production. However, under certain metabolic insults, the retina demonstrates considerable resilience and maintains ATP production, and/or retinal function. We wanted to investigate whether this resilience would be reflected in alterations in the activity of key enzymes of retinal metabolism, or enzymes associated with amino acid production that may supply their carbon skeleton for energy production. Enzymatic assays were conducted to determine the activity of key retinal metabolic enzymes total ATPase and Na(+)/K(+)-ATPase, aspartate aminotransferase and lactate dehydrogenase. In vitro anoxia led to an increase in retinal lactate dehydrogenase activity and to a decrease in retinal aspartate aminotransferase activity, without significant changes in Na(+)/K(+)-ATPase activity. In vivo inhibition of glutamine synthetase resulted in a short-term significant decrease in retinal aspartate aminotransferase activity. An increase in retinal aspartate aminotransferase and lactate dehydrogenase activities was accompanied by altered levels of amino acids in neurons and glia after partial inhibition of glial metabolism, implying that short- and long-term up- and down-regulation of key metabolic enzymes occurs to supply carbon skeletons for retinal metabolism. ATPase activity does not appear to fluctuate under the metabolic stresses employed in our experimental procedures.
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PMID:Short- and long-term enzymatic regulation secondary to metabolic insult in the rat retina. 1574 54

Our objective was to study brain amino acid metabolism in response to ketosis. The underlying hypothesis is that ketosis is associated with a fundamental change of brain amino acid handling and that this alteration is a factor in the anti-epileptic effect of the ketogenic diet. Specifically, we hypothesize that brain converts ketone bodies to acetyl-CoA and that this results in increased flux through the citrate synthetase reaction. As a result, oxaloacetate is consumed and is less available to the aspartate aminotransferase reaction; therefore, less glutamate is converted to aspartate and relatively more glutamate becomes available to the glutamine synthetase and glutamate decarboxylase reactions. We found in a mouse model of ketosis that the concentration of forebrain aspartate was diminished but the concentration of acetyl-CoA was increased. Studies of the incorporation of 13C into glutamate and glutamine with either [1-(13)C]glucose or [2-(13)C]acetate as precursor showed that ketotic brain metabolized relatively less glucose and relatively more acetate. When the ketotic mice were administered both acetate and a nitrogen donor, such as alanine or leucine, they manifested an increased forebrain concentration of glutamine and GABA. These findings supported the hypothesis that in ketosis there is greater production of acetyl-CoA and a consequent alteration in the equilibrium of the aspartate aminotransferase reaction that results in diminished aspartate production and potentially enhanced synthesis of glutamine and GABA.
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PMID:Response of brain amino acid metabolism to ketosis. 1588 76

There is little information available on the primary products of photosynthesis and the change in the activity of the associated enzymes with altitude. We studied the same in varieties of barley and wheat grown at 1300 (low altitude, LA) and 4200 m (high altitude, HA) elevations above mean sea level in the western Himalayas. Plants at both the locations had similar photosynthetic rates, leaf water potential and the chlorophyll fluorescence kinetics. The short-term radio-labelling experiments in leaves showed appearance of (14)CO(2) in phosphoglyceric acid and sugar phosphates in plants at both the LA and HA, suggesting a major role of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in CO(2) fixation in the plants at two altitudes, whereas the appearance of labelled carbon in aspartate (Asp) and glutamate (Glu) at HA suggested a role of phosphoenolpyruvate carboxylase (PEPCase) in photosynthesis metabolism. Plants at HA had significantly higher activities of PEPCase, carboxylase and oxygenase activity of Rubisco, aspartate aminotransferase (AspAT), and glutamine synthetase (GS). However, the activities of malate dehydrogenase, NAD-malic enzyme and citrate synthase were similar at the two locations. Such an altered metabolism at HA suggested that PEPCase probably captured CO(2) directly from the atmosphere and/or that generated metabolically e.g. from photorespiration at HA. Higher oxygenase activity at HA suggests high photorespiratory activity. OAA thus produced could be additionally channelised for Asp synthesis using Glu as a source of ammonia. Higher GS activity ensures higher assimilation rate of NH(3) and the synthesis of Glu through GS-GOGAT (glutamine:2-oxoglutarate aminotransferase) pathway, also as supported by the appearance of radiolabel in Glu at HA. Enhanced PEPCase activity coupled with higher activities of AspAT and GS suggests a role in conserving C and N in the HA environment.
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PMID:Effect of altitude on the primary products of photosynthesis and the associated enzymes in barley and wheat. 1645 48

Productivity of cereal crops is restricted in saline soils but may be improved by nitrogen nutrition. In this study, the effect of ionic nitrogen form on growth, mineral content, protein content and ammonium assimilation enzyme activities of barley (Hordeum vulgare cv. Alexis L.) irrigated with saline water, was determined. Leaf and tiller number as well as plant fresh and dry weights declined under salinity (120 mM NaCl). In non-saline conditions, growth parameters were increased by application of NH(4)(+)/NO(3)(-) (25:75) compared to NO(3)(-) alone. Under saline conditions, application of NH(4)(+)/NO(3)(-) led to a reduction of the detrimental effects of salt on growth. Differences in growth between the two nitrogen regimes were not due to differences in photosynthesis. The NH(4)(+)/NO(3)(-) regime led to an increase in total N in control and saline treatments, but did not cause a large decrease in plant Na(+) content under salinity. Activities of GS (EC 6.3.1.2), GOGAT (EC 1.4.1.14), PEPC (EC 4.1.1.31) and AAT (EC 2.6.1.1) increased with salinity in roots, whereas there was decreased activity of the alternative ammonium assimilation enzyme GDH (EC 1.4.1.2). The most striking effect of nitrogen regime was observed on GDH whose salinity-induced decrease in activity was reduced from 34% with NO(3)(-) alone to only 14% with the mixed regime. The results suggest that the detrimental effects of salinity can be reduced by partial substitution of NO(3)(-) with NH(4)(+) and that this is due to the lower energy cost of N assimilation with NH(4)(+) as opposed to NO(3)(-) nutrition.
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PMID:Partial substitution of NO(3)(-) by NH(4)(+) fertilization increases ammonium assimilating enzyme activities and reduces the deleterious effects of salinity on the growth of barley. 1654 90

Fourteen-day-old Phaseolus vulgaris L. cv. Top Crop (bush bean) plants were sprayed with the plant growth stimulant, potassium naphthenate (20 mm). Seven days after treatment the contents of glutamic acid dehydrogenase, glutamic-oxaloacetic transaminase, nitrate reductase, glutamine synthetase, and cytochrome oxidase in the trifoliate leaf blades of treated plants were significantly larger, and the specific activity of the last four was significantly greater. Potassium nephthenate (1 mum) in the assay solutions did not significantly alter the activity of these enzymes in the cell-free extracts of untreated plants. Leaf discs from treated plants did not incorporate (14)C-leucine into protein more actively. The protein content of leaves of treated plants was 15.3% greater, and the percentages of 16 individual amino acids in the hydrolysates of the proteins of control and treated plants showed numerous differences. The major changes were greater percentages of glutamic acid, glycine, and proline, and smaller values of arginine, lysine, tyrosine, and leucine in protein of treated plants. The content of ethanol-soluble (free) amino acids was greater by 7.5%. The principal changes in content of these acids were larger percentages of arginine and lysine, and smaller values for glutamic acid, serine, and proline in the leaves of potassium naphthenate-treated plants. The content of DNA, measured 1, 2, and 3 weeks after a foliar application of potassium naphthenate, was not significantly different from that of untreated plants, but the amount of RNA was significantly greater at all three times of measurement. The number and weight of green pods per plant 30 days after potassium naphthenate application were significantly larger, suggesting that the stimulative action of potassium naphthenate was in progress at the times of the assays. A mechanism, involving a genetic and a metabolic phase, is suggested for the stimulation of plant growth by naphthenate.
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PMID:Mechanism of plant growth stimulation by naphthenic Acid: effects on nitrogen metabolism of phaseolus vulgaris L. 1665 19

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

The free amino acid concentrations in cotyledons and axes of soybean (Glycine max [L.] Merr. cv. Wells) seedlings were determined by automated single column analysis after germination at 10 and 23 C. After 5 days germination at 10 C, glutamate and aspartate were in high concentration in both cotyledons and axes (38 and 24% of total free amino acids recovered, respectively), whereas the concentrations of their amide derivatives, asparagine and glutamine, were low in cotyledons (4.4%) and high in axes (21%). In contrast, after 5 days germination at 23 C, asparagine and glutamine accounted for 22 and 45% of total free amino acids in cotyledons and axes respectively, and aspartate and glutamate concentrations were low. The activities of glutamine synthetase and asparagine synthetase were considerably lower in tissues from the 10 C treatment than those from the 23 C treatment.Aspartate and glutamate concentrations were nearly equal in all but one sample. Both glutamate oxaloacetate transaminase and glutamate dehydrogenase activities were much higher in axis tissues at 23 C as compared to 10 C. Arrhenius plots of axis glutamate oxaloacetate transaminase and glutamate dehydrogenase activities were biphasic and triphasic, respectively, with energies of activation for both increasing with low temperature. Energies of activation were identical for glutamate oxaloacetate transaminase from 10 and 23 C treatments but much higher for glutamate dehydrogenase from 23 C-treated axes. This indicates a difference in enzyme complement for glutamate dehydrogenase with the two treatments.Hydrolysis of free amino acid sample (basic fraction) aliquots showed large quantities of peptides in 23 C-treated axes at 2 days, while few or no peptides were found in the 10 C treatment. Amino acid residues most prevalent in peptides were aspartate, threonine, serine, glutamate, and glycine.
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PMID:Low Temperature Effects on Soybean (Glycine max [L.] Merr. cv. Wells) Free Amino Acid Pools during Germination. 1666 May 75


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