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)

The aspartate and tyrosine aminotransferases from Escherichia coli have 43% sequence identity and nearly identical active sites. Both are equally good enzymes for dicarboxylate substrates, but the latter transaminates aromatic amino acids 1000 times faster. In an attempt to discover the critical residues for this differential substrate specificity, the aspartate aminotransferase mutant V39L has recently been prepared. It showed improved Kcat/Km values for aspartate, glutamate and tyrosine and the corresponding oxo acids, mainly due to two to ten times lower Km values. For example, the Km values of V39L (wild type) for Asp and Glu are 0.12 (1.0) and 0.85 (2.7) mM respectively. The mutant was co-crystallized with 30 mM maleate from both polyethylene glycol and ammonium sulfate. Both structures were solved and refined to R-factors of 0.22 and 0.20 at 2.85 and 2.5 A resolution respectively. They bear strong resemblance to the closed structure of the wild type enzyme complexed with maleate. The unexpected feature is that, for the first time, the closed form was produced in crystals grown from ammonium sulfate. It is concluded that the mutation has shifted the conformational equilibrium towards the closed form, which leads to generally reduced substrate Kms.
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PMID:Three-dimensional structure of a mutant E. coli aspartate aminotransferase with increased enzymic activity. 807 30

Quinidine in vitro significantly reduced accumulation of TEA (tetraethyl ammonium) and PAH (p-amino hippurate) and inhibited oxygen consumption in renal cortical slices. Mitochondrial respiratory control index (RCI) and ADP/O ratio were decreased. Intraperitoneal administration of quinidine at 75 mg/kg twice a day for four days inhibited TEA transport in renal cortical slices and decreased oxygen consumption. Mitochondria showed a reduction in ADP/O ratio but no change in RCI. Serum biochemical measurements indicated a significant elevation in serum creatinine, alanine aminotransferase (ALT), and aspartate aminotransferase (AST).
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PMID:In vitro and in vivo effects of quinidine on the kidneys in Fischer-344 rats. 830 84

Aspartate aminotransferase as well as valine dehydrogenase and threonine dehydratase was required for the biosynthesis of tylosin in Streptomyces fradiae NRRL 2702. The biosynthesis of these enzymes and tylosin production were repressed by high concentrations of ammonium ions. The change in specific tylosin production rates in batch cultures with different initial concentrations of ammonium ions showed patterns similar to those of the specific production rates of aspartate aminotransferase, valine dehydrogenase, and threonine dehydratase. Aspartate aminotransferase has been purified by acetone precipitation, DEAE-cellulose, hydroxyapatite, and preparative electrophoresis chromatographies. The purified enzyme (120 kDa) consisted of two subunits identical in molecular mass (54 kDa) and showed homogeneity, giving one band with a pI of 4.2 upon preparative isoelectric focusing. The enzyme was specific for L-aspartate in the forward reaction; the Km values were determined to be 2.7 mM for L-aspartate, 0.7 mM for 2-oxyglutarate, 12.8 mM for L-glutamate, and 0.15 mM for oxaloacetate. The enzyme was somewhat thermostable, having a maximum activity at 55 degrees C, and had a broad pH optimum that ranged from 5.5 to 8.0. The mode of action was a ping-pong-bi-bi mechanism.
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PMID:Aspartate aminotransferase and tylosin biosynthesis in Streptomyces fradiae. 848 Oct 8

The effects of hyperammonemia induced in vivo by injecting rats with ammonium acetate on oxidative phosphorylation, malate-aspartate shuttle, some related enzyme activities and metabolite levels in brain mitochondria were studied ex vivo. Rats were found to be either ammonia-sensitive (showing convulsions) or ammonia-resistant (without convulsions) after intraperitoneal injection of ammonium acetate (7 mmol/kg). Ammonium acetate administration to ammonia-sensitive rats led to inhibition of State 3 rates of brain mitochondria utilizing pyruvate, glutamate, isocitrate, and succinate as substrates and to decreased respiratory control index. In brain mitochondria isolated from ammonia-resistant animals, the ammonia-induced effect on such State 3 rates was not observed. In brain mitochondria from hyperammonemic rats without convulsions, a small increase in the activity of malate dehydrogenase was observed; glutamate dehydrogenase, succinate dehydrogenase, and aspartate aminotransferase were not affected. In brain mitochondria from rats with ammonia-induced convulsions, the activities of malate dehydrogenase and succinate dehydrogenase were reduced significantly. Ammonium acetate injection to rats was associated with a 5-fold increase in the brain mitochondrial ammonium ion content and a decrease (ca. 50%) in brain mitochondrial glutamate and aspartate; brain mitochondrial malate and 2-oxoglutarate levels remained unchanged. The rate of the malate-aspartate shuttle in brain mitochondria of hyperammonemic rats was decreased by 20% as compared to corresponding rate in control rats. We conclude that acute administration of ammonium acetate induces serious disturbances in the electron-transport chain, interferences of the malate-aspartate shuttle, alterations of the levels of shuttle intermediates and inhibition of the activities of malate and succinate dehydrogenases in brain mitochondria.
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PMID:Effects of acute hyperammonemia in vivo on oxidative metabolism in nonsynaptic rat brain mitochondria. 910 39

Diffraction-quality crystals of S. cerevisiae cytoplasmic aspartate aminotransferase have been obtained by the hanging-drop vapor-diffusion method in the presence of pyridoxal phosphate and maleic acid, sodium acetate, ammonium acetate and polyethylene glycol. The crystals have the symmetry of the orthorhombic space groups P212121 or P21212 with unit-cell dimensions a = 130.2, b = 134.6 and c = 98.7 A. Square rod-shaped crystals with dimensions of approximately 0.2 x 0.2 x 0.5 mm diffract to spacings of 2 A. The calculated value of the Matthews coefficient, Vm = 2.4 A3 Da-1, is consistent with four subunits of aspartate aminotransferase per asymmetric unit.
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PMID:Crystallization and preliminary X-ray diffraction analysis of aspartate aminotransferase from Saccharomyces cerevisiae. 976 67

To examine what causes increased viscosity in culture broth in Streptomyces fradiae culture, various natural nitrogen sources were investigated. Extracellular protease activity increased with culture time and decomposed the natural nitrogen source into amino acids. In the case of gluten meal, after a culture time of 5 d, concentrations of glutamic acid and aspartic acid had increased to 600 and 200 mg/L, respectively, which were about 3- and 2-fold as high as levels in cultures under similar conditions using Pharmamedia. For various amino acids tested, the addition of glutamic acid or aspartic acid mixture to the culture medium raised the apparent viscosity to its highest demonstrated value, 260 mPa.s after 5 d of culture, which was 3-fold higher than without amino acids. Consumption of the decomposed glutamic acid and aspartic acid was dependent on the activities of glutamate dehydrogenase and aspartate aminotransferase, respectively. When ammonium ion was used as the nitrogen source, cell concentration reached 1.75 g/L measured as an intracellular nucleic acid concentration, which was about 2.3-fold higher than that with any other natural nitrogen source. However, apparent viscosity was only 75 mPa.s, a value one-third that of the amino acid mixture, and 70% of the pellets were bigger than 1.2 x 10(4) microm(2). In the case of gluten meal or the amino acid mixture, pellets bigger than 1.2 x 10(4) microm(2) comprised only 8%. This demonstrates that consumption of some amino acids affected the formation of filamentous morphology, which caused an increase in the apparent viscosity of the culture broth, and the apparent viscosity was not caused by the mycelial concentration but the mycelial morphology.
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PMID:Dependence of apparent viscosity on mycelial morphology of Streptomyces fradiae culture in various nitrogen sources. 1093 23

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

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown for 68 days in a growth chamber in nutrient solutions with ammonium, nitrate or ammonium nitrate as the nitrogen source. Among the nitrogen sources tested, whole-seedling biomass, relative growth rate (RGR), root and shoot elongation, and number of lateral roots, were greatest in seedlings grown with ammonium. In the absence of nitrogen, plant growth and formation of lateral roots were poor. Initially, glutamine synthetase, NAD-glutamate dehydrogenase and aspartate aminotransferase activities were high in young roots and shoots, but all three enzymatic activities decreased after one month of culture. In root apices, glutamine synthetase and aspartate aminotransferase activities were higher than NAD-glutamate dehydrogenase activity. Enzymatic activities were often higher in ammonium-fed seedlings than in seedings supplied with the other forms of nitrogen. Activities of all three enzymes were significantly reduced in seedlings grown in the absence of nitrogen. The beneficial effect of ammonium is discussed on the basis of its involvement in the assimilation pathways of Douglas-fir.
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PMID:Effects of nitrogen source on growth and activity of nitrogen-assimilating enzymes in Douglas-fir seedlings. 1265 84

A procedure for isolation and purification of aspartate aminotransferase from wheat grain includes chromatography on DEAE cellulose, acidification-alkalization, precipitation with protamine sulfate, fractionation with ammonium sulfate, and chromatography on hydroxyapatite. The yield of protein was 27% with 95% purity. Crystals of the enzyme (0.05 x 0.025 x 0.015 mm3) were obtained from ammonium sulfate solution.
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PMID:Isolation, purification, and crystallization of aspartate aminotransferase from wheat grain. 1537 70

The effects of melatonin and dimethylsulfoxide (DMSO) on liver and brain oxidative stress, hepatic failure and blood urea nitrogen (BUN) level changes produced by a single dose of thioacetamide (TAA) in Wistar rats were studies. A dose of either melatonin (3 mg kg(-1)day(-1)) or DMSO (2 g kg(-1)day(-1)) was injected for 3 days before and for 2 days after the administration of TAA (150 mg kg(-1) i.p.). Blood samples were taken from the neck vascular in order to determine ammonium, BUN and liver enzymes. We estimated lipid peroxidation products, reduced glutathione (GSH) content and catalase activity in liver and brain homogenates. TAA caused significant increases in ammonium and in the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) enzymes, while it decreased BUN values. TAA also increased lipid peroxidation product levels, but reduced GSH content and catalase activity in the liver and brain. Both melatonin and DMSO, although melatonin more significantly, decreased the intensity of the changes produced by the administration of TAA alone. Furthermore, melatonin alone or combined with TAA increased the BUN levels and decreased the ammonia values compared with control animals. These results support the antioxidative and neuro-/hepato-protective action of melatonin and a lesser action of DMSO. Likewise, these data seem to support the hypothesis of an effect of melatonin on urea synthesis.
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PMID:Hepato- and neurotoxicity induced by thioacetamide: protective effects of melatonin and dimethylsulfoxide. 1589 75


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