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)

We present here a radiochemical enzymatic endpoint assay for the guanine nucleotides GTP and GDP that is suitable for use with cell extracts. The major coupling enzyme used is phosphoenolpyruvate carboxykinase purified from chicken liver. The ancillary coupling enzyme, aspartate aminotransferase, was used to generate a low steady-state concentration of oxalacetate. GTP was determined by the overall conversion of [U-14C]aspartate into [14C]phosphoenolpyruvate. This reaction was also scaled-up as a preparative method for [U-14C]phosphoenolpyruvate. This was used with the same coupling enzymes in reverse to measure GDP by the formation of [14C]aspartate. The assay method was applied to isolated rat hepatocytes. The total GTP and GDP concentrations found were within the range reported by others for rat liver. The advantages of this assay are its sensitivity, specificity, and applicability to large numbers of samples.
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PMID:A radiochemical enzymatic endpoint assay for GTP and GDP. 204 20

In an open, exploratory study, the safety of ursodeoxycholic acid (UDCA) in the treatment of primary biliary cirrhosis (PBC) was investigated. Seven patients in stages I to III and two patients in stage IV were treated for 1 year with 1 g/day of UDCA. Clinical symptoms, and alkaline phosphatase, gamma-glutamyltransferase, alanine aminotransferase (GOT) and aspartate aminotransferase (GTP) levels improved significantly within three months and remained at the lower levels for the period of observation. Results of the galactose elimination capacity (4.7 +/- S.D. 1.4 mg/min per kg) and the aminopyrine breath test (0.60 +/- 0.33% dose/kg per mmol CO2) remained unchanged for 1 year. In all patients total serum bile acids increased and quantitatively UDCA became the most important bile acid. In patients in stages I to III this increase, however, was modest, whereas in patients in stage IV, total serum bile acids reached levels of 140 and 157 mumol/l and UDCA, levels of 90 and 103 mumol/l, respectively. It is concluded that UDCA appears to be safe only in stages I to III and that prognostic stratification based on bile acid levels or on the histological stage of the disease should be an important aspect of controlled clinical trials.
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PMID:Ursodeoxycholic acid in primary biliary cirrhosis: no evidence for toxicity in the stages I to III. 236 81

The effect of N-benzyl-D-glucamine dithiocarbamate (BGD) on the renal toxicity of inorganic mercury in rats was studied. Rats were injected i.v. with saline or HgCl2 (300 micrograms Hg/kg) and 30 min later they were injected i.p. with saline or BGD (2778 mumol/kg, a quarter of an LD50). Urinary excretion of gamma-glutamyl-transpeptidase (gamma-GTP), which is a brush border enzyme, in rats after mercury treatment significantly increased compared to that of the control in the 12-24 h urine specimen and reached a maximum value within 24 h after the treatment. Urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG), which is a lysosomal enzyme, also significantly increased after mercury treatment compared to that of the control in the 12-24 h urine specimen and reached a maximum value within 48 h after the treatment. A change in urinary aspartate aminotransferase (AST) activity after mercury treatment followed a pattern similar to that observed with the urinary NAG. BGD treatment did not increase the urinary excretions of gamma-GTP, NAG, and AST. The uptake of p-aminohippuric acid (PAH) by renal cortical slices significantly decreased 24 h after mercury treatment. BGD injection after mercury treatment did not decrease the uptake of PAH by cortical slices. In addition, the microscopic examination of renal tissue from mercury-treated rats revealed necrosis of the proximal tubular cells. However, a photomicrograph of rat renal cortex after BGD treatment showed little abnormality. These results indicated that the mercury-induced renal damage was protected by the injection of BGD 30 min after mercury treatment.
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PMID:Effect of N-benzyl-D-glucamine dithiocarbamate on renal toxicity of inorganic mercury in rats. 239 73

We have found previously (Fahien, L.A., Kmiotek, E.H., MacDonald, M. J., Fibich, B., and Mandic, M. (1988) J. Biol. Chem. 263, 10687-10697) that glutamate-malate oxidation can be enhanced by cooperative binding of mitochondrial aspartate aminotransferase and malate dehydrogenase to the alpha-ketoglutarate dehydrogenase complex. The present results demonstrate that glutamate dehydrogenase, which forms binary complexes with these enzymes, adds to this ternary complex and thereby increases binding of the other enzymes. Kinetic evidence for direct transfer of alpha-ketoglutarate and NADH, within these complexes, has been obtained by measuring steady-state rates of E2 when most of the substrate or coenzyme is bound to the aminotransferase or glutamate dehydrogenase (E1). Rates significantly greater than those which can be accounted for by the concentration of free ligand, calculated from the measured values of the E1-ligand dissociation constants, require that the E1-ligand complex serve as a substrate for E2 (Srivastava, D. K., and Bernhard, S. A. (1986) Curr. Tops. Cell Regul. 28, 1-68). By this criterion, NADH is transferred directly from glutamate dehydrogenase to malate dehydrogenase and alpha-ketoglutarate is channeled from the aminotransferase to both glutamate dehydrogenase and the alpha-ketoglutarate dehydrogenase complex. Similar evidence indicates that GTP bound to an allosteric site on glutamate dehydrogenase functions as a substrate for succinic thiokinase. The potential physiological advantages to channeling of activators and inhibitors as well as substrates within multienzyme complexes organized around the alpha-ketoglutarate dehydrogenase complex are discussed.
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PMID:Kinetic advantages of hetero-enzyme complexes with glutamate dehydrogenase and the alpha-ketoglutarate dehydrogenase complex. 274 45

Succinate synthesis from exogenous malate, alpha-ketoglutarate, oxaloacetate and L-glutamate in isolated oxygen-deprived rat heart mitochondria was studied using 1H NMR. The highest rate of succinate synthesis was observed during incubation of mitochondria with a mixture of L-glutamate and oxaloacetate. When mitochondria were incubated with [U-13C] glutamate and oxaloacetate the [U-13C] succinate/succinate and aspartate/succinate ratios were equal to 2. This suggests that the succinate produced from [U-13C] alpha-keto-glutarate formed via transamination of [U-13C] glutamate with oxaloacetate by aspartate aminotransferase exceeds twofold that synthesized via oxaloacetate reduction. It may thus be expected that GTP yield in a reaction catalyzed by the succinic thiokinase will be 2 times higher that of ATP production coupled with NADH-dependent fumarate reduction.
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PMID:A 1H NMR study of succinate synthesis from exogenous precursors in oxygen-deprived rat heart mitochondria. 286 22

Leucine and monomethyl succinate initiate insulin release, and glutamine potentiates leucine-induced insulin release. Alanine enhances and malate inhibits leucine plus glutamine-induced insulin release. The insulinotropic effect of leucine is at least in part secondary to its ability to activate glutamate oxidation by glutamate dehydrogenase (Sener, A., Malaisse-Lagae, F., and Malaisse, W. J. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 5460-5464). The effect of these other amino acids or Krebs cycle intermediates on insulin release also correlates with their effects on glutamate dehydrogenase and their ability to regulate inhibition of this enzyme by alpha-ketoglutarate. For example, glutamine enhances insulin release and islet glutamate dehydrogenase activity only in the presence of leucine. This could be because leucine, especially in the presence of alpha-ketoglutarate, increases the Km of glutamate and converts alpha-ketoglutarate from a noncompetitive to a competitive inhibitor of glutamate. Thus, in the presence of leucine, this enzyme is more responsive to high levels of glutamate and less responsive to inhibition by alpha-ketoglutarate. Malate could decrease and alanine could increase insulin release because malate increases the generation of alpha-ketoglutarate in islet mitochondria via the combined malate dehydrogenase-aspartate aminotransferase reaction, and alanine could decrease the level of alpha-ketoglutarate via the alanine transaminase reaction. Monomethyl succinate alone is as stimulatory of insulin release as leucine alone, and glutamine enhances the action of both. Succinyl coenzyme A, leucine, and GTP are all bound in the same region on glutamate dehydrogenase, where GTP is a potent inhibitor and succinyl coenzyme A and leucine are comparable activators. Thus, the insulinotropic properties of monomethyl succinate could result from it increasing the level of succinyl coenzyme A and decreasing the level of GTP via the succinate thiokinase reaction.
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PMID:Regulation of insulin release by factors that also modify glutamate dehydrogenase. 304 28

In this paper we describe the cloning and sequence analysis of the tyrB and aspC genes from Escherichia coli K12, which encode the aromatic aminotransferase and aspartate aminotransferase respectively. The tyrB gene was isolated from a cosmid carrying the nearby dnaB gene, identified by its ability to complement a dnaB lesion. Deletion and linker insertion analysis located the tyrB gene to a 1.7-kilobase NruI-HindIII-digest fragment. Sequence analysis revealed a gene encoding a 43 000 Da polypeptide. The gene starts with a GTG codon and is closely followed by a structure resembling a rho independent terminator. The aspC gene was cloned by screening gene banks, prepared from a prototrophic E. coli K12 strain, for plasmids able to complement the aspC tyrB lesions in the aminotransferase-deficient strain HW225. Sub-cloning and deletion analysis located the aspC gene on a 1.8-kilobase HincII-StuI-digest fragment. Sequence analysis revealed the presence of a gene encoding a 43 000 Da protein, the sequence of which is identical with that previously obtained for the aspartate aminotransferase from E. coli B. Considerable overproduction of the two enzymes was demonstrated. We compared the deduced protein sequences with those of the pig mitochondrial and cytoplasmic aspartate aminotransferases. From the extensive homology observed we are able to propose that the two E. coli enzymes possess subunit structures, subunit interactions and coenzyme-binding and substrate-binding sites that are very similar both to each other and to those of the mammalian enzymes and therefore must also have very similar catalytic mechanisms. Comparison of the aspC and tyrB gene sequences reveals that they appear to have diverged as much as is possible within the constraints of functionality and codon usage.
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PMID:The cloning and sequence analysis of the aspC and tyrB genes from Escherichia coli K12. Comparison of the primary structures of the aspartate aminotransferase and aromatic aminotransferase of E. coli with those of the pig aspartate aminotransferase isoenzymes. 352 91

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

We cloned the era gene of Francisella tularensis from a plasmid library by heterologous genetic complementation of an Escherichia coli mutant conditionally defective for the production of Era, an essential protein for cell growth. Nucleotide sequence analysis indicated that, in F. tularensis, era constitutes a single gene operon. ORFs aspC and mdh encoding aspartate aminotransferase and malate dehydrogenase, respectively, flank era in F. tularensis. Although classified as Gram-, the flanking regions and the relative location of era in F. tularensis are distinctly different from those of typical Gram- and Gram+ bacteria. Computer analysis of bacterial Era protein sequences identified conserved domains in addition to the common G domains of most GTP-binding proteins.
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PMID:A Francisella tularensis DNA clone complements Escherichia coli defective for the production of Era, an essential Ras-like GTP-binding protein. 916 8

L-colitose and d-perosamine are unusual sugars found in the O-antigens of some Gram-negative bacteria such as Escherichia coli, Vibrio cholerae, and Salmonella enterica, among others. The biosynthetic pathways for these two sugars begin with the formation of GDP-mannose from d-mannose 1-phosphate and GTP followed by the subsequent dehydration and oxidation of GDP-mannose to yield GDP-4-keto-6-deoxymannose. Following the production of GDP-4-keto-6-deoxymannose, the two pathways diverge. In the case of GDP-perosamine biosynthesis, the next step involves an amination reaction at the C-4' position of the sugar, whereas in GDP-colitose production, the 3'-hydroxyl group is removed. The enzymes catalyzing these reactions are GDP-perosamine synthase and GDP-4-keto-6-deoxymannose-3-dehydratase (ColD), respectively. Both of these enzymes are pyridoxal 5'-phosphate (PLP) dependent, and their three-dimensional structures place them into the well-characterized aspartate aminotransferase superfamily. A comparison of the active site architecture of ColD from E. coli (strain 5a, type O55:H7) to that of GDP-perosamine synthase from Caulobacter crescentus CB15 suggested that only two mutations would be required to convert ColD into an aminotransferase. Here we present a combined structural and functional analysis of the ColD S187N/H188K mutant protein that, indeed, has been converted from a sugar dehydratase into an aminotransferase.
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PMID:Two site-directed mutations are required for the conversion of a sugar dehydratase into an aminotransferase. 1940 12


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