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)

L-Leucine and its nonmetabolized analogue, 2-aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH) activate glutamate dehydrogenase in pancreatic islets, whether the reaction velocity is measured in the direction of glutamate synthesis or glutamate deamination. The rate of glutamate oxidative deamination is increased by ADP and inhibited by 2-ketoglutarate, NH4+ and GTP. The islet homogenate catalyzes the transamination between L-glutamate and either 2-ketoisocaproate or pyruvate, and between 2-ketoglutarate and L-leucine, L-aspartate, L-alanine, L-isoleucine, L-valine, L-norvaline or L-norleucine, but not b (+/-) BCH. The glutamate-aspartate transaminase is preferentially located in mitochondria relative to other transaminases. The parallel effects of L-leucine and BCH on glutamate dehydrogenase and their vastly different abilities to act as transamination partners may account for both analogies and discrepancies in the metabolic and functional responses of the islets to these two branched-chain amino acids.
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PMID:The stimulus-secretion coupling of amino acid-induced insulin release. XI. Kinetics of deamination and transamination reactions. 675 75

14C-labeled bicarbonate was incorporated into trichloroacetic acid-insoluble material by cell suspensions of A. viscosus strain M100 and also into the four-carbon fermentation product, succinate, but not into the three-carbon fermentation product, lactate. The initial step in the conversion of 14C-labeled bicarbonate into both trichloroacetic acid-insoluble material and succinate was catalyzed by the enzyme phosphoenolypyruvate carboxylase, which served to convert the glycolytic intermediate, phosphoenolpyruvate, and bicarbonate to the four-carbon compound, oxalacetate. The metabolic fate of oxalacetate was its conversion to either trichloroacetic acid-insoluble material or succinate. One pathway by which oxalacetate may be metabolized into acid-insoluble material is via its conversion to the biosynthetic precursor aspartate by the action of glutamate aspartate aminotransferase. One source of the alpha-amino group of aspartate was the ammonium ion, which could be incorporated into glutamate, the substrate of the glutamate aspartate aminotransferase reaction, by the action of a reduced nicotinamide adenine dinucleotide phosphate-dependent glutamate dehydrogenase whose reducing equivalents could be derived from the nicotinamide adenine dinucleotide phosphate-dependent oxidative reactions of the hexose monophosphate pathway catalyzed by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Alternatively, oxalacetate was converted to the fermentation product, succinate, through the sequential action of malate dehydrogenase, fumarase, and succinic dehydrogenase. The resolution and partial purification of phosphoenolpyruvate carboxylase, glutamate aspartate aminotransferase, glutamate dehydrogenase, malate dehydrogenase, fumarase, and succinic dehydrogenase are also reported.
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PMID:Carbon dioxide metabolism by Actinomyces viscosus: pathways for succinate and aspartate production. 676 22

Venous blood values were determined on 19 Southdown sheep (9 adult ewes and 10 wether lambs). Principal sheep were given 12.5 ml of 3.3M urea solution/kg of body weight, which produced acute ammonia toxicosis. Whole blood ammonium-nitrogen was determined by ion exchange; venous blood gases and pH were measured with a pH blood gas analyzer; and 23 serum chemical analyses were obtained with a sequential multiple autoanalyzer computer. Analysis of variance for the data revealed significant changes for 20 values. The values are presented and discussed with regard to those that changed beyond acceptable limits (whole blood ammonium-nitrogen, venous blood pH, serum glucose, serum lactate dehydrogenase, serum alkaline phosphatase, serum creatine kinase, serum urea nitrogen, serum inorganic phosphorus, serum sodium, and serum potassium), those that changed within acceptable limits (PVo2, PVco2, serum triglycerides, serum free fatty acids, plasma volatile fatty acids, serum aspartate aminotransferase, serum total protein, serum albumin, serum creatinine, urea nitrogen-creatinine ratio, serum uric acid, serum cholesterol, serum low-density lipoproteins, serum calcium, serum iron and serum chloride), and those with no change (total and direct serum bilirubin and albumin-globulin ratio). Metabolic consequences of ammonia toxicosis are considered with regard to energy, lipid , protein, and acid-base and electrolyte balances. Blood values having possible laboratory diagnosis value and considerations for therapeutic adjustment are discussed.
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PMID:Ovine blood chemistry values measured during ammonia toxicosis. 710 77

Chronic oral administration of ammonium molybdate in rats markedly retarded the growth rate of rats and high protein diet could partially reverse this condition. The activities of several enzymes viz. acid phosphatase, alkaline phosphatase, glucose-6-phosphatase, succinic dehydrogenase, glutamate oxaloacetate transaminase, inorganic pyrophosphatase and acetylcholinesterase in different tissues and serum levels of luteinizing hormone, follicle stimulating hormone, prolactin and cortisol are altered due to the toxicity conditions and high protein diet fed group of animals showed almost normal values in respect of a few of these parameters. Normal histological pattern of both liver and kidney tissues were altered under molybdenum toxicity condition. Significant increase of basophilic substances are observed in the cytoplasm of the liver cells of the toxic group of animals which is counteracted by feeding high protein diet.
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PMID:Biochemical studies on molybdenum toxicity in rats: effects of high protein feeding. 732 62

To purify cytoplasmic and mitochondrial isoenzymes of aspartate aminotransferase (EC 2.6.1.1) from human liver. We used heat treatment, ammonium sulfate precipitation, anion- and cation-exchange chromatography, affinity chromatography, and isoelectric focusing. Final preparations of the isoenzymes were homogeneous, with specific activities of 198 and 208 kU/g for the cytoplasmic and the mitochondrial enzymes, respectively. The mitochondrial isoenzyme focused as a single band with a pl value of 9.60, whereas the cytoplasmic isoenzyme had subforms with pl values of 5.22, 5.42, and 5.62 at 4 degrees C. In Tris . HCl buffer, both isoenzymes have an activity maximum at pH 7.8. In [bis(2-hydroxyethyl)amino]tris(hydroxymethyl)methane (Bistris) buffer, however, the mitochondrial isoenzyme also showed an optimum pH of 6.7.
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PMID:Isolation and purification of aspartate aminotransferase isoenzymes from human liver by chromatography and isoelectric focusing. 746 Feb 73

The aim of this work was to assess whether perinatal hyperammonemia impairs the function of NMDA receptors and whether this impairment affords protection against acute ammonia toxicity and glutamate and NMDA neurotoxicity. Rats were exposed to ammonia during the prenatal and lactation periods by feeding the female rats an ammonium-containing diet since day 1 of pregnancy. After weaning (at postnatal day 21), the pups were fed a normal diet with no ammonia added. This treatment resulted in a marked decrease of the growth rate of the animals, which was maintained even 1 month after normalization of ammonia levels. Rats exposed to ammonia were more resistant than controls to acute ammonia toxicity 13 days after feeding a normal diet but not at 3 months. Primary cultures of cerebellar neurons from hyperammonemic rats showed decreased binding of [3H]MK-801 and were remarkably more resistant than controls to glutamate and NMDA toxicities. Also, the increase in aspartate aminotransferase activity induced by low concentrations of NMDA was not produced in such cultures. These results indicate that exposure to ammonia during the prenatal and lactation periods results in long-lasting impairment of NMDA receptor function. This would be the reason for the delayed protection afforded by exposure to low ammonia levels against acute ammonia toxicity in animals and against glutamate and NMDA toxicity in neuronal cultures.
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PMID:Prenatal exposure of rats to ammonia impairs NMDA receptor function and affords delayed protection against ammonia toxicity and glutamate neurotoxicity. 766 52

Human placental cytoplasmic aspartate transaminase was purified 404-fold by heat treatment, ammonium sulfate fractionation, dialysis and DEAE-Sephadex chromatography. The pH optimum of the enzyme was 6.8 in either phosphate or cacodylate buffer. The Km values of alpha-ketoglutarate and L-aspartate were 2.06 and 22.5 mM, respectively. A 78% inhibition of the enzyme was noted at 4 mM concentration of maleate which inhibited the enzyme upon competing with alpha-ketoglutarate with a Ki value of 1.72 mM. The kinetic properties of this enzyme are compared with those of the enzyme from various mammalian and other sources. The data are discussed in terms of the probable effectiveness of this enzyme in catabolizing L-aspartate in placenta especially after the consumption of a high protein diet by the pregnant mother.
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PMID:Partial purification and kinetic properties of human placental cytosolic aspartate transaminase. 771 46

Nitrogen regulation of tylosin synthesis in Streptomyces fradiae NRRL 2702 was studied in batch and chemostat cultures using a soluble synthetic medium. In batch cultures, valine dehydrogenase (VDH; EC 1.4.1.8), threonine dehydratase (TDT; EC 4.2.1.16) and aspartate aminotransferase (ASAT; EC 2.6.1.1) reached their highest specific activities at 120 h. The specific activities of the three enzymes showed close correlation with the value of specific tylosin formation rate (qTYL). In chemostat cultures, the maximum value of qTYL was 1.14 tylosin per mycelial mass per h (mg g-1 h-1) at the specific growth rate of 0.05 h-1, and after reaching a rate of 0.1 h-1, qTYL decreased with increasing levels of the specific growth rate. This value of qTYL was 3.5-times as large as that of maximum qTYL observed in the batch culture. The specific formation rates of VDH, TDT, ASAT and tylosin were repressed by high levels of specific ammonium ion uptake rate.
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PMID:Kinetics of the repression of tylosin biosynthesis by ammonium ion in Streptomyces fradiae. 776 61

A new crystal form of chicken cytosolic aspartate aminotransferase (EC 2.6.1.1) has been grown using a mixture of ammonium sulfate with ethanol as a precipitant. Crystals of the enzyme belong to the space group P 2(1)2(1)2(1) having the following unit cell dimensions: a = 62.38 A, b = 117.41 A, c = 124.34 A. There is one molecule of the enzyme in the asymmetric unit. The crystals diffract at 1.8 A resolution.
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PMID:[A new form of aspartate aminotransferase crystals]. 787 85

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


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