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)

Recently we reported that the contractile agonist angiotensin II induces hypertrophy, not hyperplasia, in cultured rat aortic smooth muscle cells (Geisterfer AAT, Peach MJ, Owens GK: Angiotensin II induces hypertrophy, not hyperplasia, of cultured rat aortic smooth muscle cells. Circ Res 1988;62:749-756). We have further explored the hypothesis that contractile agonists are important regulators of smooth muscle cell growth by examining the effects of another contractile agonist, arginine vasopressin, on growth of cultured rat aortic smooth muscle cells. Autoradiographic analysis as well as cell number determinations showed that arginine vasopressin (1 microM) did not stimulate proliferation in cells made quiescent in a defined serum-free media nor did it augment proliferation in 0.4% fetal bovine serum. However, flow cytometric analysis of cellular protein content demonstrated that arginine vasopressin (1 microM) did induce cellular hypertrophy in quiescent cultures after 4 days of treatment, increasing smooth muscle cell protein content by 35% as compared with vehicle-treated controls. The increase in protein content showed a concentration dependence. Cellular hypertrophy was accompanied by an increase in [35S]methionine incorporation, which was elevated 45% by 24 hours. Both the increase in [35S]methionine incorporation and the increase in protein content could be prevented by the specific arginine vasopressin receptor antagonist. [1-beta-mercapto-beta,beta-cyclopentamethylene propionic acid), 2-(O-methyl)tyrosine] arginine vasopressin. An increase in [35S]methionine incorporation was observed between 12 and 24 hours after treatment of quiescent smooth muscle cells for only 5 minutes with arginine vasopressin (1 microM). Arginine vasopressin-induced increases in [35S]methionine incorporation was increased within 6 hours after treatment. These studies show that arginine vasopressin, like angiotensin II, induces hypertrophy but not hyperplasia of cultured rat aortic smooth muscle cells.
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PMID:Arginine vasopressin-induced hypertrophy of cultured rat aortic smooth muscle cells. 279 15

A rapid, sensitive and specific procedure has been developed for the determination of p-tyrosine aminotransaminase activity. The assay is based on high-performance liquid chromatography (HPLC) separation and electrochemical detection of the pyruvate product, which has been derivatized with hydroxylamine to form a stable oxime. Using this method the product at the low pmol level can be measured. A comparison of the kinetic parameters of the rat liver tyrosine aminotransferase and rat brain non-specific aspartate aminotransferase towards p-tyrosine has been made.
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PMID:New sensitive high-performance liquid chromatographic method for p-tyrosine aminotransferase assay. 287 80

A stable activity which transfers the amino group from glutamate to prephenate was extracted from 4-day old etiolated shoots of sorghum. The activity was retained on DEAE cellulose and eluted as a single peak. Prephenate aminotransferase co-eluted with a very abundant alpha-ketoglutarate: aspartate aminotransferase, but heating at 70 degrees C resulted in loss of alpha-ketoglutarate: aspartate activity with nearly full retention of prephenate: glutamate aminotransferase activity. The heated enzyme displayed high affinity and specificity for prephenate. Among 7 donors tested, only glutamate, and aspartate at less than 20% the rate with glutamate, supported prephenate aminotransferase activity. In the reverse direction, a reaction rate comparable to that in the forward direction was unchanged as the concentration of alpha-ketoglutarate was reduced from 1.0 to 0.09 mM. The apparent Km for arogenate was 0.8 mM. The forward reaction was unaffected by the inclusion of tyrosine, phenylalanine or tryptophan. Together with the discovery of arogenate dehydrogenase in sorghum [3], these data indicate that, in the sorghum plant, tyrosine derives from prephenate by transamination and aromatization, rather than the reverse sequence.
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PMID:Tyrosine biosynthesis in Sorghum bicolor: characteristics of prephenate aminotransferase. 293 44

Resonance Raman (RR) spectra are reported for aspartate aminotransferase from pig heart cytosol, and for inhibitor complexes. They are interpreted with reference to the previously analyzed spectra of pyridoxal phosphate (PLP) Schiff base adducts. This comparison shows that, as expected, the pyridine N atom is protonated in the native enzyme at pH 5, and in the glutarate complexes at pH 8.5, and that it is also protonated in the alpha-methylaspartate complex; the stabilization of the pyridine proton at high pH must be due to the interaction with aspartate 222 seen in the x-ray crystal structure. RR spectra of the erythro-beta-hydroxy-DL-aspartate complex, representing the p-quinoid enzyme intermediate, as well as of AlIII complexes of PLP Schiff bases with phenylalanine and tyrosine ethyl ester have been obtained via the coherent anti-Stokes Raman scattering technique, and partially assigned. A novel H/D exchange at the coenzyme C4' atom has been observed for the native enzyme in D2O, and has been determined, by a combination of NMR and RR measurements, to be due to the Raman laser irradiation. This photoprocess, which is not observed for PLP Schiff bases in aqueous solution, is attributed to a photoexcited p-quinoid intermediate, similar to that implicated in the enzyme mechanism. It is suggested that this intermediate is stabilized by protein interactions which localize charge on the phenolate O atom, plausibly a hydrogen bond from the nearby tyrosine 225. H/D exchange would then follow via the aldimine-ketimine interconversion known to take place in the enzyme reaction.
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PMID:Resonance Raman spectra of the pyridoxal coenzyme in aspartate aminotransferase. Evidence for pyridine protonation and a novel photochemical H/D exchange at the imine carbon atom. 299 44

Sulfometuron methyl is a potent and specific inhibitor of acetolactate synthase II in Salmonella typhimurium. Mutant strains sensitive to sulfometuron methyl on minimal medium were isolated following mutagenesis with Tn10. A conditionally auxotrophic insertion mutant, strain SMS409, which required aspartate at high temperatures or in the presence of tyrosine, was found among the 15 mutants isolated. The Tn10 insertion in strain SMS409 was mapped by conjugation and transduction to the region between aroA and pncB at 20 min on the chromosome of S. typhimurium; this location is similar to the genetic location of aspC in Escherichia coli. The specific activity of the aspC product, aspartate aminotransferase, was severely reduced in strain SMS409. This indicated that the Tn10 insertion in strain SMS409 inactivated aspC. An aspC mutant of E. coli was also inhibited by either sulfometuron methyl or tyrosine. We present a hypothesis which relates the observed alpha-ketobutyrate accumulation in sulfometuron methyl-inhibited cultures of strain SMS409 to aspartate starvation.
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PMID:Sensitivity of a Salmonella typhimurium aspC mutant to sulfometuron methyl, a potent inhibitor of acetolactate synthase II. 300 25

The refined crystallographic structure of the "closed" conformation of chicken mitochondrial aspartate aminotransferase has been used as a template for the construction of models of the two Escherichia coli aminotransferases encoded by the tyrB and aspC genes. The main results are as follows: (1) Only minor changes are required in the coordinates of the backbone atoms to accommodate the large number of substituted side chains. (2) All deletions and insertions required to allow maximum primary sequence alignment are on the solvent-accessible surface. (3) Charged residues are all located on the surface, in contact with solvent, except for certain conserved active site residues. (4) The close packing within the hydrophobic core is maintained. (5) The interactions between the subunits are maintained. (6) Modeling of tyrosine as an external aldimine into the active sites points to several residues that could be involved in determining the substrate specificities of these aminotransferases.
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PMID:Modeling the three-dimensional structures of bacterial aminotransferases. 307 20

The crucial step in enzymatic transamination is the tautomerization of aldimine/ketimine intermediates, formed between the pyridoxyl coenzyme and the amino/keto acid substrate, which is catalyzed primarily by the active site residue Lys-258 (Malcolm, B. A., and Kirsch, J. F. (1985) Biochem. Biophys. Res. Commun. 132, 915-921; W. L. Finlayson and J. F. Kirsch, in preparation). Tyr-70 is localized in close proximity to Lys-258 and, in addition, forms a hydrogen bond with the coenzyme phosphate. Tyr-70 has been postulated to have an important role in the tautomerization (Kirsch, J. F., Eichele, G., Ford, G. C., Vincent, M. G., Jansonius, J. N., Gehring, H., and Christen, P. (1984) J. Mol. Biol. 174, 497-525). This hypothesis has now been tested by the construction and analysis of a mutant Escherichia coli aspartate aminotransferase in which Tyr-70 has been changed to Phe (Y70F). Y70F retains at least 15% of the maximal activity of the wild type enzyme (WT) (kcat = 170 +/- 15 s-1 for WT versus greater than or equal to 26 +/- 3 s-1 for Y70F and shows increased Michaelis constants for both substrates (KmAsp = 2.5 +/- 0.4 mM; Km alpha Kg = 0.59 +/- 0.08 mM for WT versus KmAsp = 3.9 +/- 0.3 mM; Km alpha Kg = 2.70 +/- 0.02 mM for Y70F (where alpha Kg is alpha-ketoglutarate) ). The spectrophotometrically determined pK a values of the internal aldimines formed between pyridoxal 5'-phosphate (PLP) and Lys-258 are identical for WT and Y70F. In assays where excess L-aspartate and excess PLP are incubated with either WT or Y70F, the mutant enzyme converts the free PLP to free pyridoxamine 5'-phosphate 80-fold faster than WT (k = (3.75 +/- 0.23) X 10(-2)s-1 for Y70F versus (4.90 +/- 0.02) X 10(-4)s-1 for WT). Y70F also converts free pyridoxamine 5'-phosphate to free PLP faster than WT. Thus, Y70F dissociates coenzyme more readily than does WT. It therefore appears that the role of Tyr-70 is mainly in preventing the dissociation of the coenzyme from the enzyme. Tyr-70 does not function in an essential chemical step.
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PMID:Tyrosine 70 increases the coenzyme affinity of aspartate aminotransferase. A site-directed mutagenesis study. 330 7

After surgical placement of end-to-side portacaval shunts (PCS), 4 adult mongrel dogs (11.8 to 18.2 kg) were fed purified diets and monitored for approximately 50 weeks for changes in body weight, neurologic status, and an array of clinically important biochemical variables. Two healthy dogs, fed the same diets and maintained in the same environment, were also observed (controls). Body weights were relatively stable over the period of observation. The branched-chain ratio ([valine] + [leucine] + [isoleucine]/[phenylalanine] + [tyrosine]), an index of the degree of change in plasma amino acid concentrations, was significantly lower in dogs with PCS than in controls. Despite this depression in branched-chain ratio, the principals (dogs with PCS) were essentially free of neurologic symptoms. Statistically significant decreases due to portacaval shunting were seen in the serum concentrations of glucose, calcium, urea nitrogen, creatinine, cholesterol, and albumin. Total protein, globulin, and triglyceride concentrations tended to be lower in the serum of principals than in serum of controls, but the differences were not statistically significant. Statistically significant increases due to portacaval shunting were seen in plasma concentrations of total conjugated bile acids and sulfobromophthalein retention. Concentrations of the following compounds tended to be higher in serum of principals than in serum of controls: phosphorus, chloride, uric acid, total bilirubin, lactate dehydrogenase, aspartate transaminase, alanine transaminase, and alkaline phosphatase. Liver biopsy at 7 months after operation showed mild-to-extensive atrophy of hepatocytes, mild-to-extensive fibrosis, and collapsed portal veins in all principals examined.
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PMID:Long-term biochemical and physiologic effects of surgically placed portacaval shunts in dogs. 395 18

4-Fluorophenylalanine-resistant mutants of Salmonella typhimurium were isolated in which tyrosine pathway enzymes were not repressed by l-tyrosine. The mutants produced elevated levels of 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (tyr) and chorismate mutase T-prephenate dehydrogenase, and these enzymes as well as transaminase A were not repressed by high concentrations of tyrosine. Genetic analysis revealed that a mutation in a gene designated tyrR was responsible for the constitutivity of the tyrosine pathway enzymes in strains SG1, SG7, and SG9, and that tyrR was linked to pyrF. In strain SG1 a mutation had also occurred in aroF, the structural gene for DAHP synthetase (tyr), resulting in loss of sensitivity of this enzyme to end-product inhibition. There appeared to be no relationship between loss of feedback inhibition and loss of end-product repression, since derivative strains of SG1 that carried only the tyrR mutation behaved like the singly mutated tyrR strains, SG7 and SG9, in showing high constitutive levels of tyrosine-specific enzymes that were not repressed by tyrosine.
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PMID:tyrR, a regulatory gene of tyrosine biosynthesis in Salmonella typhimurium. 414 3

Mutants of Escherichia coli K-12 were isolated in which the synthesis of the following, normally repressible enzymes of aromatic biosynthesis was constitutive: 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetases (phe and tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A. In the wild type, DAHP synthetase (phe) was multivalently repressed by phenylalanine plus tryptophan, whereas DAHP synthetase (tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A were repressed by tyrosine. DAHP synthetase (tyr) and chorismate mutase T-prephenate dehydrogenase were also repressed by phenylalanine in high concentration (10(-3)m). Besides the constitutive synthesis of DAHP synthetase (phe), the mutants had the same phenotype as strains mutated in the tyrosine regulatory gene tyrR. The mutations causing this phenotype were cotransducible with trpA, trpE, cysB, and pyrF and mapped in the same region as tyrR at approximately 26 min on the chromosome. It is concluded that these mutations may be alleles of the tyrR gene and that synthesis of the enzymes listed above is controlled by this gene. Chorismate mutase P and prephenate dehydratase activities which are carried on a single protein were repressed by phenylalanine alone and were not controlled by tyrR. Formation of this protein is presumed to be controlled by a separate, unknown regulator gene. The heat-stable phenylalanine transaminase and two enzymes of the common aromatic pathway, 5-dehydroquinate synthetase and 5-dehydroquinase, were not repressible under the conditions studied and were not affected by tyrR. DAHP synthetase (trp) and tryptophan synthetase were repressed by tryptophan and have previously been shown to be under the control of the trpR regulatory gene. These enzymes also were unaffected by tyrR.
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PMID:Repression of aromatic amino acid biosynthesis in Escherichia coli K-12. 439 41


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