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)

Aromatic amino acid aminotransferase (ArAT) from Escherichia coli was overexpressed in E. coli cells, purified, and characterized. The enzyme was similar to aspartate aminotransferase (AspAT) of E. coli in many aspects, such as gross protein structure and spectroscopic properties. The reactions of pyridoxal 5'-phosphate-form ArAT with amino acids and pyridoxamine 5'-phosphate-form ArAT with oxo acids were investigated using stopped-flow spectrophotometric techniques. The kinetic parameters for these "half" reactions could excellently explain the ArAT-catalyzed overall transamination reactions at pH 8.0. Reactions of ArAT with aspartate and tryptophan which had been deuterated at position 2 showed isotope effects of 2.5 and 6.0 in the kcat values of the half-reactions, showing that the proton-transfer step is at least partially rate-limiting for these reactions. ArAT and AspAT showed overlapping substrate specificity. Both ArAT and AspAT were active toward dicarboxylic substrates. ArAT showed, however, 10(3)-fold higher activity toward aromatic substrates than AspAT. This high activity toward aromatic substrates was in part ascribed to the active site hydrophobicity of ArAT, which was suggested to be about 1.4 times as large as that of AspAT. In addition to dicarboxylic substrate analogs, aromatic substrate analogs such as carboxylic acids, 2-methyl amino acids, and 3-hydroxy amino acids caused characteristic changes in the absorption spectra of ArAT, while these aromatic analogs did not significantly change the spectra of AspAT. In particular, the erythro-3-hydroxy analogs of phenylalanine and aspartate caused a prominent absorption of ArAT at around 500 nm, which is generally ascribed to the accumulation of quinonoid intermediates. The threo forms of these 3-hydroxy analogs acted as substrates for ArAT. The erythro and threo forms of 3-hydroxyaspartate reacted with AspAT similarly as they reacted with ArAT; however, both forms of 3-phenylserine were poor substrates for AspAT, although phenylalanine was a fairly good substrate for AspAT. The observations on the two erythro-3-hydroxy amino acids show the similar orientation of these analogs in the active site of ArAT, probably through a hydrogen-bonding network involving the hydroxy groups of the analogs and Tyr70, and suggest that the aromatic binding pocket is near or even overlaps the side-chain-carboxylate-binding site for dicarboxylic substrates.
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PMID:Escherichia coli aromatic amino acid aminotransferase: characterization and comparison with aspartate aminotransferase. 821

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing 120, 210 and 300 g crude protein/kg diet and 0, 1.67 or 16.7 g added tryptophan (TRP)/kg diet. The hypothesis tested was that crude protein levels and TRP would affect both growth and neurotransmitter metabolism. Heart, brain and pancreatic neurotransmitter (noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxy-indole-3-acetic acid (5-HIAA)) concentrations were determined by HPLC separation and electrochemical detection. Malate dehydrogenase (2-oxoglutarate decarboxylating) (NADP+) (MDH(NADP+); EC 1.1.1.40), isocitrate dehydrogenase (NADP+) (ICD(NADP+); EC 1.1.1.42) and aspartate aminotransferase (AAT; EC 2.6.1.1) activities were also measured. Supplemental TRP decreased growth and feed intake. Increasing dietary crude protein decreased MDH(NADP+), but increased (ICD(NADP+) and AAT activities. Additional dietary TRP decreased MDH(NADP+) activity, but had no effect on other enzyme activities. Cardiac NA concentrations were directly related to dietary crude protein levels while pancreatic levels were inversely related. An increase in dietary crude protein decreased both brain NA and DA. Supplemental dietary TRP increased both 5-HIAA and 5-HT. Changes in feed intake caused by different levels of both dietary crude protein and TRP are accompanied by altered levels of neurotransmitters. The present study indicates that much larger amounts of TRP are required to make simultaneous changes in feed intake and neurotransmitters.
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PMID:Crude protein and supplemental dietary tryptophan effects on growth and tissue neurotransmitter levels in the broiler chicken. 877 19

In the end-stage renal disease patient, certain uremic compounds could influence the cellular accumulation of aluminum (Al). In this study, we examined the effect of 15 uremic ultrafiltrate fractions obtained by HPLC on the uptake and toxicity of Al in mouse hepatocytes (MH) in culture, a model system in which Al is taken up bound to transferrin (Tf). Uremic fractions 4 to 8, 12, 14, and 15 increased cellular Al uptake and aspartate aminotransferase release and decreased cell growth when Tf-Al, not Al citrate, was added to culture media. Compounds that have been extracted previously from these ultrafiltrate fractions (p-cresol, xanthine, tryptophan, hippuric acid, and o-hydroxyhippuric acid) were then tested for their effect on Al uptake and toxicity in MH at concentrations found in uremic serum. Significant Al uptake by MH was observed only when p-cresol was added together with Tf-Al. Time-response curves showed increased Al uptake and toxicity at p-cresol concentrations of 3 mg/dl in culture media. Dose-response curves confirmed that Al uptake and cell toxicity were proportional to p-cresol from 1.5 mg/dl to 3 mg/dl in culture media. p-Cresol was not toxic to MH in the absence of Tf-Al in media. p-Cresol increased Tf-associated Al uptake only because there was no effect on Al uptake when Al citrate was substituted, and studies with Tf-I125-Al in the presence of this compound showed increased Tf-I125 taken up by MH. p-Cresol did not increase Tf saturation with Al. p-Cresol also increased Tf-Al uptake in Friend erythroleukemia and neuroblastoma cells in culture. Our studies suggest that p-cresol and uremic fractions 4 to 8, 12, 14, and 15 increase the uptake and toxicity of Al in cultured MH. These compounds may play a role in the accumulation and toxicity of Al in the liver of end-stage renal disease patients and possibly in all cells that express Tf receptors.
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PMID:P-Cresol, a uremic compound, enhances the uptake of aluminum in hepatocytes. 918 61

1. Living-related liver transplantation has some advantages in the evaluation of novel clinical protocols, since many complicated factors affecting initial graft function are almost uniform in grafts obtained from healthy donors. 2. To compare histidine-tryptophan-ketoglutarate (HTK) and University of Wisconsin (UW) solution in terms of tissue oxygenation in living-related liver transplantation, oxygen saturation of haemoglobin (SO2) in hepatic tissue and its heterogeneity (CV, coefficient of variation) were measured by near-infrared spectroscopy. The HTK and UW groups consisted of 15 and 49 successful transplants respectively, in which no statistical differences in background were observed. 3. In the HTK group, hepatic SO2 after portal vein reflow was higher (P < 0.01) than that in the UW group, as was that after hepatic artery reflow (P < 0.05). In the UW group, hepatic SO2 remained at the lower level at the end of the operation. 4. Furthermore, the increase in CV after portal vein reflow was normalized after hepatic artery reflow in the HTK group. However, the CV remained at a high level at the end of the operation in the UW group. 5. Postoperative peak aspartate aminotransferase level in the HTK group was lower than that in the UW group (P < 0.05). 6. In cadaveric liver transplantation, higher hepatic SO2 and lower CV of hepatic SO2 in the early phase after reperfusion compared with the UW group (n = 18) were also observed in the HTK group (n = 30) (P < 0.05). 7. In conclusion, recovery of tissue oxygenation and its heterogeneity after reperfusion in HTK-preserved livers were more rapid and homogeneous than in UW-preserved livers in living-related liver transplantation. Accordingly, HTK solution may be a potential alternative to UW solution.
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PMID:Hepatic preservation with histidine-tryptophan-ketoglutarate solution in living-related and cadaveric liver transplantation. 927 7

The aim of these investigations was to examine the influence of "natural fibrous feedstuffs" as wheat bran and alfalfa meal on criteria of vitamin B6 metabolism of adult sows subjected to a low vitamin B6 supply. Two experiments were conducted in two periods with 12 sows (180 kg BW) and 3 groups each. The supplements were in the first experiment 0 g, 225 g and 675 g wheat bran, and in the second experiment 0 g, 575 g and 1150 g alfalfa meal to a compound feed, low in vitamin B6 content. The criteria were fecal and urinary vitamin B6 concentration and excretion, vitamin B6 concentration in blood, hematological criteria, activity of aspartate aminotransferase in erythrocytes (EAST) and xanthurenic acid excretion in the tryptophan load test. Vitamin B6 concentration in feces amounted 10-12 micrograms/g DM and was neither influenced by quality or amount of the fibrous products. Vitamin B6 excretion was increased by each supplement and 60-70% of vitamin B6 was excreted via feces. Fecal vitamin B6 excretion was enlarged linearly by increasing fibrous supplementation. Bacterially fermentable substrates from wheat bran induced a higher bacterial vitamin B6 synthesis compared to cellulose.
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PMID:[The effect of wheat bran and green meal supplements on vitamin B6 metabolism of sows fed suboptimal vitamin B6 supply]. 932 21

To better understand how an enzyme controls cofactor chemistry, we have changed a tryptophan synthase residue that interacts with the pyridine nitrogen of the pyridoxal phosphate cofactor from a neutral Ser (beta-Ser377) to a negatively charged Asp or Glu. The spectroscopic properties of the mutant enzymes are altered and become similar to those of tryptophanase and aspartate aminotransferase, enzymes in which an Asp residue interacts with the pyridine nitrogen of pyridoxal phosphate. The absorption spectrum of each mutant enzyme undergoes a pH-dependent change (pKa approximately 7.7) from a form with a protonated internal aldimine nitrogen (lambdamax = 416 nm) to a deprotonated form (lambdamax = 336 nm), whereas the absorption spectra of the wild type tryptophan synthase beta2 subunit and alpha2 beta2 complex are pH-independent. The reaction of the S377D alpha2 beta2 complex with L-serine, L-tryptophan, and other substrates results in the accumulation of pronounced absorption bands (lambdamax = 498-510 nm) ascribed to quinonoid intermediates. We propose that the engineered Asp or Glu residue changes the cofactor chemistry by stabilizing the protonated pyridine nitrogen of pyridoxal phosphate, reducing the pKa of the internal aldimine nitrogen and promoting formation of quinonoid intermediates.
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PMID:Mutation of an active site residue of tryptophan synthase (beta-serine 377) alters cofactor chemistry. 956 51

The gene encoding aspartate aminotransferase from the psychrophilic bacterium Pseudoalteromonas haloplanktis TAC 125 was cloned, sequenced and overexpressed in Escherichia coli. The recombinant protein (PhAspAT) was characterized both at the structural and functional level in comparison with the E. coli enzyme (EcAspAT), which is the most closely related (52% sequence identity) bacterial counterpart. PhAspAT is rapidly inactivated at 50 degrees C (half-life = 6.8 min), whereas at this temperature EcAspAT is stable for at least 3 h. The optimal temperature for PhAspAT activity is approximately 64 degrees C, which is some 11 degrees C below that of EcAspAT. The protein thermal stability was investigated by following changes in both tryptophan fluorescence and amide ellipticity; this clearly suggested that a first structural transition occurs at approximately 50 degrees C for PhAspAT. These results agree with the expected thermolability of a psychrophilic enzyme, although the observed stability is much higher than generally found for enzymes isolated from cold-loving organisms. Furthermore, in contrast with the higher efficiency exhibited by several extracellular psychrophilic enzymes, both kcat and kcat/Km of PhAspAT are significantly lower than those of EcAspAT over the whole temperature range. This behaviour possibly suggests that the adaptation of this class of endocellular enzymes to a cold environment may have only made them less stable and not more efficient. The affinity of PhAspAT for both amino-acid and 2-oxo-acid substrates decreases with increasing temperature. However, binding of maleate and 2-methyl-L-aspartate, which both inhibit the initial steps of catalysis, does not change over the temperature range tested. Therefore, the observed temperature effect may occur at any of the steps of the catalytic mechanism after the formation of the external aldimine. A molecular model of PhAspAT was constructed on the basis of sequence homology with other AspATs. Interestingly, it shows no insertion or extension of loops, but some cavities and a decrease in side chain packing can be observed.
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PMID:Aspartate aminotransferase from the Antarctic bacterium Pseudoalteromonas haloplanktis TAC 125. Cloning, expression, properties, and molecular modelling. 1078 2

Aspartate aminotransferases have been cloned and expressed from Crithidia fasciculata, Trypanosoma brucei brucei, Giardia intestinalis, and Plasmodium falciparum and have been found to play a role in the final step of methionine regeneration from methylthioadenosine. All five enzymes contain sequence motifs consistent with membership in the Ia subfamily of aminotransferases; the crithidial and giardial enzymes and one trypanosomal enzyme were identified as cytoplasmic aspartate aminotransferases, and the second trypanosomal enzyme was identified as a mitochondrial aspartate aminotransferase. The plasmodial enzyme contained unique sequence substitutions and appears to be highly divergent from the existing members of the Ia subfamily. In addition, the P. falciparum enzyme is the first aminotransferase found to lack the invariant residue G197 (P. K. Mehta, T. I. Hale, and P. Christen, Eur. J. Biochem. 214:549-561, 1993), a feature shared by sequences discovered in P. vivax and P. berghei. All five enzymes were able to catalyze aspartate-ketoglutarate, tyrosine-ketoglutarate, and amino acid-ketomethiobutyrate aminotransfer reactions. In the latter, glutamate, phenylalanine, tyrosine, tryptophan, and histidine were all found to be effective amino donors. The crithidial and trypanosomal cytosolic aminotransferases were also able to catalyze alanine-ketoglutarate and glutamine-ketoglutarate aminotransfer reactions and, in common with the giardial aminotransferase, were able to catalyze the leucine-ketomethiobutyrate aminotransfer reaction. In all cases, the kinetic constants were broadly similar, with the exception of that of the plasmodial enzyme, which catalyzed the transamination of ketomethiobutyrate significantly more slowly than aspartate-ketoglutarate aminotransfer. This result obtained with the recombinant P. falciparum aminotransferase parallels the results seen for total ketomethiobutyrate transamination in malarial homogenates; activity in the latter was much lower than that in homogenates from other organisms. Total ketomethiobutyrate transamination in Trichomonas vaginalis and G. intestinalis homogenates was extensive and involved lysine-ketomethiobutyrate enzyme activity in addition to the aspartate aminotransferase activity. The methionine production in these two species could be inhibited by the amino-oxy compounds canaline and carboxymethoxylamine. Canaline was also found to be an uncompetitive inhibitor of the plasmodial aspartate aminotransferase, with a K(i) of 27 microm.
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PMID:Methionine regeneration and aspartate aminotransferase in parasitic protozoa. 1144 76

The aim of present experiment was to study the changes of corticosterone, insulin and glucose levels in plasma, of the activity of enzymes involved in aminoacid metabolism in liver and the binding of insulin to specific receptors of cell membrane from liver and also of adipose tissue of rats exposed to space flight for 14 days on biosatellite Cosmos 2044. Adult male Wistar rats (body mass 300-370 g) were divided into five groups: intact control rats (AC), rats exposed to space flight (F), animals in synchronous model experiment (S), rats in antiorthostatic hypokinesia (A) and so called operated control group (C). Half of all groups (5 animals) except the intact control were operated 3 days before the experiment (fibulas on both hind legs were broken). The flight animals were sacrificed 5-6 hours after landing. It was observed that plasma insulin levels are increased in rat exposed to 14-day space flight and in synchron experiments. A significant increase of plasma glucose levels was found in flight rats in spite of high insulin concentrations suggesting that in rats exposed to 14-day space a deterioration of tissue sensitivity to insulin could by present. No significant differences of specific insulin binding to liver plasma membrane fraction in flight and intact control animals were observed. A decrease of insulin binding capacity in liver was found in rats in antiorthostatic hypokinesia (A). However in the membrane of adipocytes an important increase of insulin receptors was noted in rats subjected to space flight. These results suggest, that the liver and adipocyte insulin receptors of flight rats did not respond to the increased plasma insulin levels by "down regulation". The determination of plasma corticosterone levels showed that in flight rats and animals exposed to antiorthostatic hypokinesia the plasma hormone levels are significantly elevated. A significant increase of tyrosine aminotransferase and tryptophan pyrrolase activities in liver of flight rats and those exposed to hypokinesia was observed. Also the elevation of alanine amino-transferase in liver was observed in flight rats, while, the activity of aspartate aminotransferase in liver was similar in control and flight animals. These results showed that the changes in liver enzyme activities in rats after 14-day space flight are in agreement with the results observed in previous experiments after a shorter space flight (7 days).
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PMID:The effect of space flight on the board of the satellite Cosmos 2044 on plasma hormone levels and liver enzyme activities of rats. 1154 60

The activity of the enzymes involved in aminoacid metabolism (tyrosine aminotransferase, TAT, tryptophan pyrrolase TP, serine dehydratase, SD) with rapid response to glucocorticoids and enzymes requiring for activity increase repeated administration of corticosterone (alanine aminotransferase, ALT, aspartate aminotransferase, AST) in liver, the changes of lipolysis in adipose tissue and the plasma corticosterone levels were studied in rats subjected to space flight (F), in animals from synchron model experiments (SM, simulated conditions of space flight in laboratory) and in intact controls (C). The increase of plasma corticosterone concentration and of the activity of rapidly (TAT, TP, SD) and slowly activating enzymes (ALT, AST) was found in F group 6-10 hr after space flight (18.5 days on biosatellite COSMOS 1129). This suggested the presence of acute-stress (associated primarily with the landing) and chronic stress induced hypercorticosteronemia during the flight. After the short 6-day period of recovery the plasma corticosterone concentrations and the activities of liver enzymes returned to control levels. The exposition of animals to repeated immobilization stress showed higher response of corticosterone levels in flight rats as compared to intact controls. No changes in basal lipolysis were observed in flight rats in comparison to intact controls, however the stimulation of lipolysis by norepinephrine was lower in animals from F and SM groups. This lower response of lipolytic processes to norepinephrine was found in flight animals also after six days period of recovery. These results showed that there are important changes in the regulation of lipolytic processes in adipose tissue of rats after space flight and in the conditions of model experiments.
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PMID:Metabolic changes in the animals subjected to space flight. 1154 92


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