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)

Primary cultures of adult rat hepatocytes were incubated (1.5-16 hr) with various concentrations of CCl4 (less than or equal to 0.5 mM) and/or CHCl3 (less than or equal to 2.5 mM). Agent-dependent alterations in hepatocyte functions were assessed by measuring (1) [3H]choline incorporation into phosphatidylcholine (endoplasmic reticulum), (2) MTT (tetrazolium salt) reduction (mitochondria), and (3) AST release into medium (plasma membrane). Cultured hepatocytes incubated with 0.5 mM CCl4 displayed a significant (p less than or equal to 0.001) and rapid (1.5 hr) reduction (40%) in endoplasmic reticulum function that preceded significant (p less than or equal to 0.001) alterations in mitochondria (6-16 hr) and plasma membrane (6-16 hr) functions. CCl4-dependent alterations in liver cell functions are a result of CCl4 bioactivation since metyrapone inhibits the CCl4-mediated changes in cell functions. Response surface methods (RSM) were used to determine the influence of combinations of CCl4 and CHCl3 on liver cell MTT reduction and [3H]choline incorporation. Regression coefficients were determined for CCl4, CHCl3, and CCl4-CHCl3. All results were significant (p less than 0.0001) and implied that CCl4 was a more potent hepatotoxin in vitro than CHCl3. The RSM analysis also suggested that combinations of CHCl3 and CCl4 have greater than additive effects on MTT reduction and [3H]choline incorporation. These effects of CCl4 and/or CHCl3 on liver cell functions in vitro are consistent with liver alterations observed in vivo. Therefore, primary cultures of adult rat hepatocytes may be an appropriate model in vitro to assess the hepatotoxic potential of agents alone or in combination.
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PMID:Toxic interactions between carbon tetrachloride and chloroform in cultured rat hepatocytes. 279 11

This paper describes in vitro studies on the effects of environmental pollutants (SO2/NOx) in biological systems. Basic physical, chemical and biochemical parameters were analyzed to establish the rate of SO2/NOx absorption by the culture medium. It was shown that the pH remains constant for 24 h of exposure to gas concentrations up to 50 p.p.m. The concentration of ions resulting from absorption of each pollutant in the liquid phase is dependent on their concentration in the gas phase and on exposure time. Short exposure times and high gas dosages resulted in similar doses in the medium as long exposure periods and low gas dosages. The activities of a human serum standard (alkaline phosphatase, ALP; aspartate amino transferase, AST; alanine amino transferase, ALT; gamma-glutamyltransferase, gamma-GT; lactate dehydrogenase, LDH) were determined after gaseous exposure to SO2 and NOx. The results revealed a distinct decrease in the activity of LDH after 1, 3 and 5 h exposure to 200 p.p.m. SO2. The effects of the pollutants were assayed in vitro using fetal hamster lung cells (FHLC), rat hepatocytes and the cell line CO60. For the determination of toxic effects, it was shown that the plating efficiency was a more sensitive parameter than the assay for trypan blue exclusion. Toxicity indicated as an increase of LDH leakage was not observed from FHLC in culture. Instead, a decrease of LDH was found following SO2 exposition. This decrease was similar to that observed for the human serum standard. The induction of DNA single-strand breaks was determined as a measure of genotoxic effects. SO2 application decreased the rate of DNA single-strand breaks induced by N-nitroso-acetoxymethyl-methylamine in both FHLC and in rat hepatocytes. SO2 or NOx treatment of CO60 cells for 1 h did not result in the induction of DNA amplification. HSO3- added directly to the medium as the sodium salt, however, distinctly induced the amplification of SV40 DNA. The amplification rates induced by benzo[a]pyrene or dimethylbenzanthracene were neither influenced by SO2, NOx nor HSO3-. An additive effect of HSO3- with either benzo[a]pyrene or dimethylbenzanthracene for this biological parameter was therefore not observed.
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PMID:Effects of SO2 or NOx on toxic and genotoxic properties of chemical carcinogens. I. In vitro studies. 283 97

Sodium valproate (VPA), the salt of a branched short-chain fatty acid, is a major antiepileptic whose mode of action, as yet unclear, may involve effects on the organization of membranes. VPA was either injected into rats whose liver and kidney mitochondria were then isolated, or was preincubated with isolated mitochondria. First, liver and kidney mitochondria were studied with paramagnetic probes. The electron paramagnetic resonance spectra of proteins of VPA-treated mitochondria spin-labeled with 4-maleimido-2,2,6,6-tetramethyl-1-pyrrolidinoxyl showed that the ratio of weakly immobilized to strongly immobilized SH groups was reduced with respect to control mitochondria, more so in liver than in kidney mitochondria of VPA-injected rats, and more so in kidney than in liver mitochondria for VPA-incubated mitochondria. Spectra of mitochondrial lipids spin-labeled with 5-doxyl stearic methyl ester showed that VPA had no significant effect on order parameters S. Second, the transmembrane movement of aspartate aminotransferase was studied by incubating liver mitochondria in a sucrose-succinate medium and then fractionating them. The translocation of aspartate aminotransferase from mitoplasts, vesicles formed of inner membrane and matrix, to the intermembrane fluid, was significantly higher in VPA-treated than in control mitochondria. Thus, VPA, at concentrations in the range of those used therapeutically, interacted with membranes by modifying the structural organization of the internal mitochondrial membrane, essentially the membrane protein conformation.
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PMID:Effects of sodium valproate on mitochondrial membranes: electron paramagnetic resonance and transmembrane protein movement studies. 301 82

X-ray crystallographic data have implicated Arg-292 as the residue responsible for the preferred side-chain substrate specificity of aspartate aminotransferase. It forms a salt bridge with the beta or gamma carboxylate group of the substrate [Kirsch, J. F., Eichele, G., Ford, G. C., Vincent, M. G., Jansonius, J. N., Gehring, H., & Christen, P. (1984) J. Mol. Biol. 174, 497-525]. In order to test this proposal and, in addition, to attempt to reverse the substrate charge specificity of this enzyme, Arg-292 has been converted to Asp-292 by site-directed mutagenesis. The activity (kcat/KM) of the mutant enzyme, R292D, toward the natural anionic substrates L-aspartate, L-glutamate, and alpha-ketoglutarate is depressed by over 5 orders of magnitude, whereas the activity toward the keto acid pyruvate and a number of aromatic and other neutral amino acids is reduced by only 2-9 fold. These results confirm the proposal that Arg-292 is critical for the rapid turnover of substrates bearing anionic side chains and show further that, apart from the desired alteration, no major perturbations of the remainder of the molecule have been made. The activity of R292D toward the cationic amino acids L-arginine, L-lysine, and L-ornithine is increased by 9-16-fold over that of wild type and the ratio (kcat/KM)cationic/(kcat/KM)anionic is in the range 2-40-fold for R292D, whereas this ratio has a range of [(0.3-6) x 10(-6)]-fold for wild type. Thus, the mutation has produced an inversion of the substrate charge specificity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Role of arginine-292 in the substrate specificity of aspartate aminotransferase as examined by site-directed mutagenesis. 316

Experimental and clinical experience with compounds containing antimony have shown that the trivalent compounds are generally more toxic than the pentavalent ones. APT can cause severe pain and tissue necrosis and is therefore not given by intramuscular or subcutaneous injection. APT has the actions and uses of AST, but it is less soluble and more irritating than the sodium salt which is therefore more suitable for intravenous use. Trivalent antimony compounds are toxic when used topically. Adverse effects are similar for all trivalent compounds, and include nausea, vomiting, weakness and myalgia, abdominal colic, diarrhoea, and skin rashes, including pustular eruptions. Hypersensitivity reactions also occur. Respiratory symptoms include cough, dyspnoea, and chronic lung changes. Cardiotoxicity is the most important and may produce arrhythmias, myocardial depression and damage, Stokes-Adams attacks, heart failure, and cardiac arrest. Hepatic damage and necrosis, as well as blood dyscrasias, may occur. Toxic effects on the kidney may follow chronic use. Continuous treatment with small doses of antimony may give rise to symptoms of subacute poisoning, similar to those of chronic arsenic poisoning, due to accumulation of antimony in the body, especially if trivalent compounds are used, because of their long biological half-lives. Reproductive disorders and chromosome damage have been reported; antimony compounds are, therefore, potentially toxic to reproduction and have mutagenic, and oncogenic potential. Antimony compounds should, therefore, not be used during pregnancy or in the presence of hepatic, renal, or heart disease. Pentavalent antimony preparations especially the organic compounds, together with non-metallic synthetic preparations, such as the diamidines, have now replaced APT for use in leishmaniasis. Because of the toxicity of antimony compounds, investigations have been undertaken to reduce their adverse effects by combining them with chelating agents. These preparations appear to have reduced the toxic effects of antimony without affecting the efficacy of the preparations. Liposome-encapsulated antimony products have, more recently, been shown to be much less toxic because of the reduced dose of the antimony compound required for effective therapy. The historical uses of antimony were based on the belief that the topical and systemic adverse effects, for example, skin eruptions and diarrhoea and vomiting, were signs that the condition being treated was responding by being brought to the surface to relieve congestion at the diseased area. There is no evidence in topical use, but there is evidence that such use can cause severe reactions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Toxicity of antimony and its compounds. 330 36

A 32-year-old male (Mr. A.), monitored during an 8-d heat acclimation (HA) investigation, unexpectedly exhibited heat intolerance and heat exhaustion. Thirteen other males completed HA without indications of either heat intolerance or heat exhaustion. Because Mr. A. responded normally to HA on days 1-4, the intervention of an unknown host factor on days 5-8 was suggested. Mr. A.'s heat exhaustion episode (day 8) was apparently forewarned by loss of body weight and increased delta HR, delta Tsk (days 5-8) and delta Tre (days 7-8) during daily 90-min trials. His symptoms indicated classical salt depletion heat exhaustion, but the calculated salt deficit (less than 0.1 g NaCl.kg-1 body weight) was mild. Post-heat exhaustion serum enzyme levels were either normal (ALT, AST) or acutely elevated (CPK). Blood beta-endorphin and cortisol levels were six times and two times greater than control values, respectively. This case report is unique because clinical/physiological measurements and blood analyses were performed before, during, and after heat intolerance and heat exhaustion.
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PMID:Heat intolerance, heat exhaustion monitored: a case report. 335 82

A lead-salt procedure was used for the cytochemical demonstration of aspartate aminotransferase (AT) in the CA3 of the rat hippocampus. Cytoplasmic- and mitochondrial-AT isoenzymes were demonstrated in different neuronal structures, but not in astrocytes. Of special interest was the localization of cytoplasmic AT in most mossy-fibre boutons. This might indicate that cytoplasmic AT is responsible for the production of releasable glutamate in the glutamatergic/aspartatergic mossy fibre system.
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PMID:Cytochemical demonstration of aspartate aminotransferase in the mossy-fibre system of the rat hippocampus. 369 29

beta-Sulfopyruvic acid (2-carboxy-2-oxoethanesulfonic acid) is prepared in greater than 90% yield by reaction of bromopyruvic acid with sodium sulfite. beta-[35S]Sulfopyruvate is prepared by transamination between [35S]cysteinesulfonate (cysteate) and alpha-ketoglutarate using mitochondrial aspartate aminotransferase isolated from rat liver. Following either chemical or enzymatic synthesis, the crude reaction product is conveniently purified by chromatography on Dowex 1; beta-sulfopyruvate is isolated as the stable, water-soluble dilithium salt. beta-Sulfopyruvate is shown to be an alternative substrate of mitochondrial malate dehydrogenase; in the presence of 0.25 mM NADH, beta-sulfopyruvate is reduced with an apparent Km of 6.3 mM and a Vmax equal to about 40% of that observed with oxaloacetate. This finding forms the basis of a convenient spectrophotometric assay of beta-sulfopyruvate.
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PMID:beta-Sulfopyruvate: chemical and enzymatic syntheses and enzymatic assay. 374 Apr 6

It was recently suggested that the apparent biliary transport maximum (Tm, secretory maximum) for bile salts is primarily determined by their degree of cytotoxicity (the cytotoxicity hypothesis), based on experiments on male rats [Hardison, W. G., D. E. Hatoff, K. Miyai, and R. G. Weiner. Am. J. Physiol. 241 (Gastrointest. Liver Physiol. 4): G337-G343, 1981]. To confirm this hypothesis, we determined the Tm of three different bile salts, taurocholate (TC), taurochenodeoxycholate (TCDC), and tauroursodeoxycholate (TUDC) in female rats and hamsters. The order of Tm values in female rats was the same as that reported for male rats (TUDC greater than TC greater than TCDC), whereas in female hamsters it was TC greater than TCDC greater than TUDC. On the other hand, in hamsters, the order of cytotoxicity, evaluated in vivo by the biliary excretion of hepatocyte enzymes such as lactate dehydrogenase and alkaline-phosphatase and an increase in plasma lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase levels under a fixed rate infusion (0.6 and 1.2 mumol X min-1 X 100 g body wt-1) of bile salts, was inverse to the order of Tm values (TCDC greater than TC greater than TUDC) in rats, but in hamsters, too, TCDC was most cytotoxic. The order of Tm value in hamsters thus does not correspond to the order of cytotoxicity of these bile salts, suggesting that the cytotoxicity of bile salts may not be the sole determinant of bile salt Tm.
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PMID:Differing transport maxima values for taurine-conjugated bile salts in rats and hamsters. 378 51

We examined 17 lots of 2-oxoglutarate (seven acid forms, three K salt forms, and seven Na salt forms), obtained from eight commercial suppliers, for suitability for measuring aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2) in human serum. Measurements of the catalytic activity concentrations of these two aminotransferases with each of these 17 preparations were not sufficiently sensitive to distinguish good from poor-quality material. Thus, we ranked these lots for purity, by specific analysis with glutamate dehydrogenase and by liquid chromatography, and determined the water content, acid content, and spectral characteristics of each. On the basis of a 2-oxoglutarate assay value by glutamate dehydrogenase of 98% or greater, we considered seven of the preparations acceptable and 10 unacceptable. The molar absorptivities (L X mol-1 X cm-1, mean +/- SD) of the seven acceptable lots in 1 mol/L HCl were: epsilon 325 nm = 9.12 +/- 0.02 (CV = 0.2%), epsilon 279 nm = 2.63 +/- 0.23 (CV = 9.9%), and epsilon 245 nm = 37.9 +/- 4.1 (CV = 10.9%). Use of these spectrophotometric limits alone unambiguously distinguished the inferior lots of 2-oxoglutarate. We urge the inclusion of detailed spectrophotometric specifications for 2-oxoglutarate in Reference Methods for aminotransferase measurements.
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PMID:Comparisons of 17 lots of 2-oxoglutarate, and specifications for use of this substrate in reference methods. 399 57


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