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)

Plasma L-arginine is usually deficient immediately after hepatic reperfusion in orthotopic liver transplantation, which may also contribute to the occurrence of either hepatic ischemia-reperfusion injury or pulmonary hypertension. In this study, exogenous L-arginine was thus experimentally used to reverse the deficient status of the L-arginine/NO pathway. An in vivo model of 1 hr hepatic ischemia and reperfusion was thus tested in both rats (Experiment A) and pigs (Experiment B). In Experiment A, 10 mg/kg of L-arginine (group 1, n = 7), D-arginine (group 2, n = 7), or saline (group 3, n = 7) was administered through the portal vein. The hepatic tissue blood flow, at 20 min after reperfusion, improved in group 1 (70.7 +/- 7.0% of the preclamp levels) compared to groups 2 and 3. The serum glutamate oxaloacetate transaminase levels at 24 hr after reperfusion were also lower in group 1 (320 +/- 22.2 IU/L) than in either group 2 or group 3. The intrahepatic NO levels showed a temporal burst (> 15,000 pA current) after reperfusion only in group 1. In Experiment B, 10 mg/kg of L-arginine (group 4, n = 5), D-arginine (group 5, n = 5), or 10 ml of saline (group 6, n = 5) was administered through the portal vein. In group 4, the MPAP (mean pulmonary arterial pressure)/MAP (mean arterial pressure) was lower than that observed in groups 5 and 6. In conclusion, exogenous L-arginine administered from the portal vein was thus found to be effective in mitigating both portal hypertension and reperfusion injury by producing an increased amount of NO immediately after reperfusion.
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PMID:Role of exogenous L-arginine in hepatic ischemia-reperfusion injury. 922 19

To evaluate the role of nitric oxide (NO) in hepatic microcirculation and liver injury during endotoxemia, we studied O2 transport in the hepatic microcirculation of endotoxin-infused rats. Rats were continuously infused with Escherichia coli lipopolysaccharide (LPS) (0.8 mg/kg/h) for 7 hours. LPS increased the plasma levels of NO2- + NO3- and aspartate transaminase (AST), and decreased the bile flow rate and hepatic adenosine triphosphate (ATP) level. Hepatic microcirculation was evaluated by two methods: reflectance spectrophotometry showed a decrease in the oxygenation of hemoglobin (Hb) in the liver, and dual-spot microspectroscopy indicated that LPS administration decreased blood velocity, the oxygenation of Hb, and O2 release from sinusoids to hepatocytes. The observed decreases in the O2 transport parameters were prominent in pericentral sinusoids. All of these phenomena were further aggravated by the administration of N(w)-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg/h) plus LPS, and by aminoguanidine (AMG) (5 mg/kg/h) plus LPS, and these could be reversed by the concomitant administration of L-arginine (L-Arg) (100 mg/kg/h). These results suggest that deterioration of hepatic oxygen transport and liver function induced by endotoxin can be ameliorated by NO.
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PMID:Role of nitric oxide in oxygen transport in rat liver sinusoids during endotoxemia. 925 43

The primary role of Tyr225 in the aspartate aminotransferase mechanism is to provide a hydrogen bond to stabilize the 3'O- functionality of bound pyridoxal phosphate. The strength of this hydrogen bond is perturbed by replacement of Tyr225 with 3-fluoro-L-tyrosine (FlTyr) by in vitro transcription/translation. This mutant enzyme exhibits kcat/values that are near to those of wild type enzyme; however, the kcat/vs pH profile is much sharper with similar pKas of approximately 7.5 for both the ascending and descending limbs. The pKas are assigned to the endocyclic proton of the internal aldimine and to the bridging hydrogen bond, respectively. The pKas in the kcat vs pH profile of 7.2 and 8.7 are assigned to the epsilon-NH3+ of lysine 258 and to the endocyclic protons of the ketimine complex, respectively. Arginine 292 forms a salt bridge with the beta-COOH of the substrate, aspartate. An improvement on the earlier attempt to invert the substrate charge specificity via R292D mutation-induced arginine transaminase activity [Cronin, C. N., & Kirsch, J. F. (1988) Biochemistry 27, 4572-4579] is described. Here Arg292 is replaced with homoglutamate (R292hoGlu). This construct exhibits 6.8 x 10(4)-fold greater activity for the cationic substrate D,L-[Calpha-3H]-alpha-amino-beta-guanidinopropionic acid (D,L-[Calpha-3H]AGPA) than does wild type enzyme. The gain in selectivity for this substrate is at least 4500-fold greater than that achieved in the 1988 experiment, i.e., [(kcat/KM)R292hoGlu/(kcat/KM)WT (D,L-[Calpha-3H]AGPA)] >/= 4500 x [(kcat/KM)R292D/(kcat/KM)WT (L-arginine)]. The value of (kcat/KM)R292D is 0.43 M-1 s-1 with L-Arg while (kcat/KM)R292hoGlu is 29 M-1 s-1 with D,L-[Calpha-3H]AGPA (it is assumed that the D-enantiomer is unreactive). The latter value is the lower limit because of the uncertain value of 3H kinetic isotope effect.
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PMID:Noncoded amino acid replacement probes of the aspartate aminotransferase mechanism. 926 32

Arg386 and Arg292 of aspartate aminotransferase bind the alpha and the distal carboxylate group, respectively, of dicarboxylic substrates. Their substitution with lysine residues markedly decreased aminotransferase activity. The kcat values with L-aspartate and 2-oxoglutarate as substrates under steady-state conditions at 25 degrees C were 0.5, 2.0, and 0.03 s-1 for the R292K, R386K, and R292K/R386K mutations, respectively, kcat of the wild-type enzyme being 220 s-1. Longer dicarboxylic substrates did not compensate for the shorter side chain of the lysine residues. Consistent with the different roles of Arg292 and Arg386 in substrate binding, the effects of their substitution on the activity toward long chain monocarboxylic (norleucine/2-oxocaproic acid) and aromatic substrates diverged. Whereas the R292K mutation did not impair the aminotransferase activity toward these substrates, the effect of the R386K substitution was similar to that on the activity toward dicarboxylic substrates. All three mutant enzymes catalyzed as side reactions the beta-decarboxylation of L-aspartate and the racemization of amino acids at faster rates than the wild-type enzyme. The changes in reaction specificity were most pronounced in aspartate aminotransferase R292K, which decarboxylated L-aspartate to L-alanine 15 times faster (kcat = 0.002 s-1) than the wild-type enzyme. The rates of racemization of L-aspartate, L-glutamate, and L-alanine were 3, 5, and 2 times, respectively, faster than with the wild-type enzyme. Thus, Arg --> Lys substitutions in the active site of aspartate aminotransferase decrease aminotransferase activity but increase other pyridoxal 5'-phosphate-dependent catalytic activities. Apparently, the reaction specificity of pyridoxal 5'-phosphate-dependent enzymes is not only achieved by accelerating the specific reaction but also by preventing potential side reactions of the coenzyme substrate adduct.
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PMID:Active-site Arg --> Lys substitutions alter reaction and substrate specificity of aspartate aminotransferase. 926 27

Tacrine is an acetylcholinesterase inhibitor approved for the treatment of Alzheimer's disease. Unfortunately, reversible hepatotoxicity in about 30% of patients at therapeutic doses limits clinical use. The purpose of this study was to develop and characterize a model of tacrine hepatotoxicity to begin to understand the mechanisms of injury. Rats were given tacrine (10-50 mg/kg, intragatrically) and killed 24 hr later. An increase in serum aspartate aminotransferase was observed up to 35 mg/kg and histology revealed pericentral necrosis and fatty changes. Aspartate aminotransferase was increased from 12 to 24 hr and returned to control values by 32 hr. Livers were perfused in a nonrecirculating system to measure oxygen uptake and trypan blue was infused at the end of each experiment to evaluate tissue perfusion. Time for trypan blue to distribute evenly throughout the liver 3 hr after tacrine treatment was significantly increased (6.9 +/- 1.3 min) compared to controls (1.0 +/- 0.3 min) reflecting decreased tissue perfusion. Tacrine also significantly increased the binding of a hypoxia marker, pimonidazole, in pericentral regions almost 3-fold, and increased portal pressure in vivo significantly. It is hypothesized that tacrine, by inhibiting acetylcholine breakdown in the celiac ganglion, increases sympathetic activity in the liver leading to vascular constriction, hypoxia and liver injury. To test this hypothesis, the hepatic nerve was severed and animals were allowed to recover before tacrine treatment. This procedure significantly reduced serum aspartate aminotransferase, time of dye distribution, pimonidazole binding and portal pressure. Furthermore, a free radical adduct was detected with spin trapping and electron spin resonance spectroscopy 8 hr after tacrine treatment, providing evidence for reoxygenation. When catechin (100 mg/kg, i.p.), a free radical scavenger, was given before tacrine, injury was decreased by about 45%. Furthermore, feeding 5% arginine in the diet significantly reduced portal pressure and time of dye distribution. These data are consistent with the hypothesis that tacrine hepatotoxicity is a hypoxia-reoxygenation injury mediated through the sympathetic nervous system.
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PMID:Development and characterization of a new model of tacrine-induced hepatotoxicity: role of the sympathetic nervous system and hypoxia-reoxygenation. 931 76

We tested the hypothesis that nutritional state affects seawater acclimation by transferring either fed or food-deprived (2 weeks) male tilapia (Oreochromis mossambicus) from fresh water to full-strength sea water. Food-deprivation resulted in a significant increase in plasma concentrations of Na+, Cl-, cortisol, glucose, total amino acid, glutamate, serine and alanine, and in hepatic pyruvate kinase (PK) and lactate dehydrogenase (LDH) activities, whereas the prolactin-188 to prolactin-177 ratio (tPRL188:tPRL177) and plasma prolactin-188 (tPRL188), lactate, arginine and hepatic glycogen content and hepatic alanine aminotransferase (AlaAT) and 3-hydroxyacyl-Coenzyme A dehydrogenase (HOAD) activities were lower than in the fed group. Seawater transfer significantly increased the tPRL188:tPRL177 ratio and plasma concentrations of Na+, Cl-, K+, growth hormone (GH), glucose, aspartate, tyrosine, alanine, methionine, phenylalanine, leucine, isoleucine and valine levels as well as gill Na+/K+-ATPase activity and hepatic PK and LDH activities, whereas plasma tPRL177, tPRL188, glycine and lysine concentrations were significantly lower than in fish retained in fresh water. There was a significant interaction between nutritional state and salinity that affected the tPRL188:tPRL177 ratio and plasma concentrations of Cl-, GH, glucose, aspartate, tyrosine, serine, alanine, glycine, arginine and hepatic PK, LDH, AlaAT, aspartate aminotransferase, glutamate dehydrogenase and HOAD activities. These results, taken together, indicate that food-deprived fish did not regulate their plasma Cl- levels, despite an enhancement of plasma hormonal and metabolic responses in sea water. Our study also suggests the possibility that plasma prolactin and essential amino acids may be playing an important role in the seawater acclimation process in tilapia.
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PMID:Food-deprivation affects seawater acclimation in tilapia: hormonal and metabolic changes 932 Mar 94

The physiological features of the mildiomycin production by Streptoverticillium rimofaciens were examined in iron-sufficient and -deficient media. Activities of NADP-linked glutamate dehydrogenase (GDH) and aspartate aminotransferase (AAT) were markedly enhanced by the addition of 10 micrograms/ml of ferrous ion into culture. Ammonium nitrogen assimilation increased with the increase in mildiomycin production. These indicate that ferrous ion contributes the supply of amino acids as a precursor of mildiomycin production. In the iron-sufficient medium, glutamate, aspartate, serine and arginine in cells were 2 to 10-fold to those in the iron-deficient medium. The major amino acid excreted from cells was arginine in the iron-sufficient culture, while in the iron-deficient culture, valine. Change in the amino acid profile by addition of ferrous ion was useful for mildiomycin biosynthesis, in which ferrous ion played a leading role in amino acid metabolism.
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PMID:Effect of ferrous ion on amino acid metabolism in mildiomycin production by Streptoverticillium rimofaciens 943 91

5-Aminolevulinate synthase (EC 2.3.1.37) catalyzes the first reaction in the heme biosynthetic pathway in nonplant eukaryotes and some prokaryotes. Homology sequence modeling between 5-aminolevulinate synthase and some other alpha-family pyridoxal 5'-phosphate-dependent enzymes indicated that the residue corresponding to the Arg-439 of murine erythroid 5-aminolevulinate synthase is a conserved residue in this family of pyridoxal 5'-phosphate-dependent enzymes. Further, this conserved arginine residue in several enzymes, e.g., aspartate aminotransferase, for which the three-dimensional structure is known, has been shown to interact with the substrate carboxyl group. To test whether Arg-439 is involved in substrate binding in murine erythroid 5-aminolevulinate synthase, Arg-439 and Arg-433 of murine erythroid 5-aminolevulinate synthase were each replaced by Lys and Leu using site-directed mutagenesis. The R439K mutant retained 77% of the wild-type activity; its K(m) values for both substrates increased 9-13-fold, while the activity of R433K increased 2-fold and the K(m) values for both substrates remained unchanged. R439L had no measurable activity as determined using a standard 5-aminolevulinate synthase enzyme-coupled activity assay. In contrast, the kinetic parameters for R433L were comparable to those of the wild-type. Dissociation constants (Kd) for glycine increased 5-fold for R439K and at least 30-fold for R439L, while Kd values for glycine for both R433K and R433L mutants were similar to those of the wild-type. However, there was not much difference in methylamine binding among the mutants and the wild-type, excepting of a 10-fold increase in K(d)methylamine for R439L. R439K proved much less thermostable than the wild-type enzyme, with the thermotransition temperature, T1/2, determined to be 8.3 degrees C lower than that of the wild-type enzyme. In addition, in vivo complementation analysis demonstrated that in the active site of murine erythroid 5-aminolevulinate synthase, R439 is contributed from the same subunit as K313 (which is involved in the Schiff base linkage of the pyridoxal 5'-phosphate cofactor) and D279 (which interacts electrostatically with the ring nitrogen of the cofactor), while another subunit provides R149. Taken together, these findings suggest that Arg-439 plays an important role in substrate binding of murine erythroid 5-aminolevulinate synthase.
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PMID:Role of arginine 439 in substrate binding of 5-aminolevulinate synthase. 948 17

Hepatic ischaemia/reperfusion is characterized by circulatory and metabolic derangement, liver dysfunction, and tissue damage. To evaluate the role of L-arginine, a substrate of nitric oxide, in ischaemia/reperfusion injury, total liver ischaemia was induced for 120 min in 22 Landrace x Large White female pigs, which were randomly assigned to a treatment group (10 animals) or a control group (12 animals). An L-arginine bolus (540 mg/kg i.v.) was administered to the treatment group 1 h before clamping the hepatic hilum, at clamping, at reperfusion, and at 1 and 2 h after reperfusion. The control animals received normal saline and an i.v. infusion. Liver function tests and analysis of serum, erythrocyte, and tissue malondialdehyde contents were performed at commencement of laparotomy, before reperfusion, and at 30 min and 7 days after reperfusion. Liver biopsies were taken at laparotomy, at 30 min, and at 7 days after reperfusion for histological and ultrastructural examination. Assessment of apoptosis included in situ end-labelling analysis and DNA gel electrophoresis. Survival at 7 days was better in the treated animals than in the controls (9/10 vs. 7/12). Tissue malondialdehyde content, aspartate aminotransferase, and lactate dehydrogenase levels were lower in the treatment group, in which morphological changes were significantly less evident than in the controls 30 min after reperfusion. At 7 days, differences between the groups with respect to cell integrity were apparent only on ultrastructural analysis. Glycogen content, 7 days after reperfusion, was higher in the treatment group than in the controls: 70.25 per cent vs. 21.66 per cent positive hepatocytes (score 3 vs. score 1). Multiparametric analysis showed fewer apoptotic cells in the treatment group at all times. Our data show that the administration of L-arginine reduces damage to liver tissue after ischaemia/reperfusion injury in a pig model. This may be explained not only by the known vasodilator, anti-aggregation, and superoxide inactivation effects of increased nitric oxide release, but possibly also by some other action of L-arginine, such as its influence on cellular metabolism.
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PMID:The protective effects of L-arginine after liver ischaemia/reperfusion injury in a pig model. 949 66

Two experiments were conducted with cross-bred barrows to determine the effect of somatotropin administration on liver enzyme activities. In the first experiment, pigs growing from 26 to 55 kg body weight were given two doses of pituitary porcine somatotropin (pST; 0 and 100 micrograms per kg body weight) and three levels of dietary energy (60, 80 and 100% of free choice intake). In the second experiment, pigs growing from 30 to 60 kg body weight were given two doses of recombinant porcine somatotropin (rpST; 0 and 100 micrograms per kg body weight) and five levels of dietary crude protein (110, 150, 190, 230 and 270 g crude protein/kg diet). Liver arginase (ARG, EC 3.5.3.1) and aspartate aminotransferase (AAT, EC 2.6.1.1) activities were then determined in organ samples taken at slaughter time. Dietary energy did not change liver ARG. Activities of both ARG and AAT increased as dietary crude protein increased. Both pST and rpST decreased ARG, AAT and serum utrea nitrogen. There was a lack of interaction between rpST therapy and dietary protein on either ARG or AAT activities, suggesting that set nutritional states are not required for expression of pST effects.
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PMID:Porcine somatotropin, dietary protein and energy effects on arginase and transaminase activities in pigs. 950 51


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