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)

The apoenzyme form of cytosolic aspartate aminotransferase of pig hearts was allowed to react at room temperature with 1 equiv of pyridoxal 5'-sulfate. The resulting covalently modified enzyme was degraded with pepsin. Fluorescent tri-, tetra-, and hexapeptides were isolated and characterized as fragments of the active site sequence: Phe-Ser-Lys-Asn-Phe-Gly-Leu. This sequence contains a modified form (Lys) of lysine-258 that is known to form a Schiff base with pyridoxal phosphate in the active site. The peptides were further degraded by acid hydrolysis to give a fluorescent derivative of lysine with light absorption and chemical properties similar to those of the original modified enzyme. A related series of peptides were obtained from apoenzyme after reaction with the 5-carboxyethenyl analogue of pyridoxal 5'-phosphate.
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PMID:Covalently modified peptides isolated from aspartate aminotransferase after reaction with pyridoxal 5'-sulfate. 717 51

We studied the effects on 25 analytes of duration of contact of serum with non-anticoagulated blood and of temperature. Serum was separated after blood was allowed to stand, for 0, 2, 4, 6, 8, 24, or 48 h at 4, 23, or 30 degrees C. Results obtained for bilirubin, albumin, zinc sulfate turbidity, thymol turbidity, cholinesterase (EC 3.1.1.8), alkaline phosphatase (EC 3.1.3.1), leucine aminopeptidase (EC 3.4.11.1), amylase (EC 3.2.1.2), total cholesterol, triglycerides, beta-lipoprotein, serum urea nitrogen, creatinine, uric acid, and gamma-glutamyltransferase (EC 2.3.2.2) were not influenced by storage at 4, 24, or 30 degrees C for as long as 48 h. Negligible differences were seen for potassium in sera in contact with cells as long as 24 h at 23 degrees C and for inorganic phosphorus after 48 h at 4 degrees C. However, at 4 degrees C we noted an increase at 8 h, a slight decrease at 30 degrees C. Statistically significant changes were seen for total protein and calcium after 48 h at 30 degrees C; for aspartate aminotransferase (EC 2.6.1.1), and alanine aminotransferase (EC 2.6.1.2), between 8 and 24 h at 23 degrees C and as soon as 6 h at 30 degrees C; for lactate dehydrogenase (EC 1.1.1.27) after 8 h at 30 degrees C and between 8 and 24 h at 23 degrees C; for glucose at 24, 4, or 2 h of storage at 4, 23, or 30 degrees C, respectively; for inorganic phosphorus after 48 h at 23 degrees C or 8 h at 30 degrees C; for potassium after 4 h at 4 degrees C or 24 h at 30 degrees C; and for sodium after 48 h at 4 degrees C or 6 h at 23 or 30 degrees C.
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PMID:Serum-constituents analyses: effect of duration and temperature of storage of clotted blood. 744 20

To purify cytoplasmic and mitochondrial isoenzymes of aspartate aminotransferase (EC 2.6.1.1) from human liver. We used heat treatment, ammonium sulfate precipitation, anion- and cation-exchange chromatography, affinity chromatography, and isoelectric focusing. Final preparations of the isoenzymes were homogeneous, with specific activities of 198 and 208 kU/g for the cytoplasmic and the mitochondrial enzymes, respectively. The mitochondrial isoenzyme focused as a single band with a pl value of 9.60, whereas the cytoplasmic isoenzyme had subforms with pl values of 5.22, 5.42, and 5.62 at 4 degrees C. In Tris . HCl buffer, both isoenzymes have an activity maximum at pH 7.8. In [bis(2-hydroxyethyl)amino]tris(hydroxymethyl)methane (Bistris) buffer, however, the mitochondrial isoenzyme also showed an optimum pH of 6.7.
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PMID:Isolation and purification of aspartate aminotransferase isoenzymes from human liver by chromatography and isoelectric focusing. 746 Feb 73

J.M., a healthy, 25-year-old male, volunteered for a study involving warfarin and acetaminophen. Acetaminophen 1 g four times a day was started for 21 days. Liver function tests taken at regular intervals for the first 12 days were unremarkable. On day 18, however, aspartate aminotransferase (AST) was 527 IU/liter and alanine aminotransferase (ALT) was 166 IU/liter. Acetaminophen was discontinued and serum transaminase levels returned to baseline levels two weeks later (AST = 26, ALT = 20). Analysis of J.M.'s urine samples over the first 18 days showed excretion patterns of glucuronide, sulfate, and glutathione derived cysteine and mercapturic acid conjugates were similar to the other subjects in the study. Acetaminophen causes hepatotoxicity in overdose or malnourished or alcoholic patients, none of which applied to our subject. Differences in metabolic activation and capacity for glutathione synthesis can predispose individuals given therapeutic doses of acetaminophen to adverse effects. Failure to detoxify a highly reactive metabolite, formed by P-450 metabolism, via glutathione conjugation is responsible for the development of acute hepatic necrosis. Accumulation of the toxic metabolite due to depleted glutathione stores may have occurred with prolonged high dosing in our subject and been responsible for his abnormal rise in liver enzymes.
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PMID:Abnormal serum transaminases following therapeutic doses of acetaminophen in the absence of known risk factors. 755 49

In vitro techniques make a major contribution to the development of alternatives to the in vivo "Draize" skin irritation test, and the development of sensitive and generally applicable in vitro endpoints of cutaneous toxicity is an area of intensive research. To investigate in vitro characteristics of cutaneous irritation, skin explants of rabbit and human origin were topically exposed to chemical irritants, after which the culture medium was analyzed for the presence of metabolites of both arachidonic and linoleic acid. In rabbits exposed to the potent irritant benzalkonium chloride, a direct relation was established between clinical signs of irritation and in vitro release of the proinflammatory mediator 12-hydroxyeicosatetraenoic acid (12-HETE) by the exposed skin. Histological examination revealed varying degrees of epidermal damage. 12-HETE was also the predominant hydroxy fatty acid released in a dose-dependent way by rabbit skin cultures after in vitro exposure to sodium dodecyl sulfate (SDS), benzalkonium chloride (BC), and formaldehyde (FA). Human skin cultures released, in addition to 12-HETE, predominantly 15-HETE and 13-hydroxyoctadecadienoic acid (13-HODE), omega-6 oxygenase products of arachidonic acid and linoleic acid, respectively. The irritant-induced release of hydroxy fatty acids was strongly inhibited by the lipoxygenase inhibitor eicosatetraynoic acid, indicating enzyme-mediated generation of these bioactive lipids. Comparison of hydroxy fatty acid release to more established markers of cytotoxicity (leakage of the cellular enzymes, such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH)) revealed that increased levels of 13-HODE, 9-HODE, 12-HETE, and ALT were specific markers of cutaneous irritancy in rabbit skin cultures.
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PMID:Release of arachidonic and linoleic acid metabolites in skin organ cultures as characteristics of in vitro skin irritancy. 760 24

Human placental cytoplasmic aspartate transaminase was purified 404-fold by heat treatment, ammonium sulfate fractionation, dialysis and DEAE-Sephadex chromatography. The pH optimum of the enzyme was 6.8 in either phosphate or cacodylate buffer. The Km values of alpha-ketoglutarate and L-aspartate were 2.06 and 22.5 mM, respectively. A 78% inhibition of the enzyme was noted at 4 mM concentration of maleate which inhibited the enzyme upon competing with alpha-ketoglutarate with a Ki value of 1.72 mM. The kinetic properties of this enzyme are compared with those of the enzyme from various mammalian and other sources. The data are discussed in terms of the probable effectiveness of this enzyme in catabolizing L-aspartate in placenta especially after the consumption of a high protein diet by the pregnant mother.
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PMID:Partial purification and kinetic properties of human placental cytosolic aspartate transaminase. 771 46

A new crystal form of chicken cytosolic aspartate aminotransferase (EC 2.6.1.1) has been grown using a mixture of ammonium sulfate with ethanol as a precipitant. Crystals of the enzyme belong to the space group P 2(1)2(1)2(1) having the following unit cell dimensions: a = 62.38 A, b = 117.41 A, c = 124.34 A. There is one molecule of the enzyme in the asymmetric unit. The crystals diffract at 1.8 A resolution.
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PMID:[A new form of aspartate aminotransferase crystals]. 787 85

hisH encodes imidazole acetol phosphate (IAP) aminotransferase in Zymomonas mobilis and is located immediately upstream of tyrC, a gene which codes for cyclohexadienyl dehydrogenase. A plasmid containing hisH was able to complement an Escherichia coli histidine auxotroph which lacked the homologous aminotransferase. DNA sequencing of hisH revealed an open reading frame of 1,110 bp, encoding a protein of 40,631 Da. The cloned hisH product was purified from E. coli and estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to have a molecular mass of 40,000 Da. Since the native enzyme had a molecular mass of 85,000 Da as determined by gel filtration, the active enzyme species must be a homodimer. The purified enzyme was able to transaminate aromatic amino acids and histidine in addition to histidinol phosphate. The existence of a single protein having broad substrate specificity was consistent with the constant ratio of activities obtained with different substrates following a variety of physical treatments (such as freeze-thaw, temperature inactivation, and manipulation of pyridoxal 5'-phosphate content). The purified enzyme did not require addition of pyridoxal 5'-phosphate, but dependence upon this cofactor was demonstrated following resolution of the enzyme and cofactor by hydroxylamine treatment. Kinetic data showed the classic ping-pong mechanism expected for aminotransferases. Km values of 0.17, 3.39, and 43.48 mM for histidinol phosphate, tyrosine, and phenylalanine were obtained. The gene structure around hisH-tyrC suggested an operon organization. The hisH-tyrC cluster in Z. mobilis is reminiscent of the hisH-tyrA component of a complex operon in Bacillus subtilis, which includes the tryptophan operon and aroE. Multiple alignment of all aminotransferase sequences available in the database showed that within the class I superfamily of aminotransferases, IAP aminotransferases (family I beta) are closer to the I gamma family (e.g., rat tyrosine aminotransferase) than to the I alpha family (e.g., rat aspartate aminotransferase or E. coli AspC). Signature motifs which distinguish the IAP aminotransferase family were identified in the region of the active-site lysine and in the region of the interdomain interface.
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PMID:Imidazole acetol phosphate aminotransferase in Zymomonas mobilis: molecular genetic, biochemical, and evolutionary analyses. 788 15

The aspartate and tyrosine aminotransferases from Escherichia coli have 43% sequence identity and nearly identical active sites. Both are equally good enzymes for dicarboxylate substrates, but the latter transaminates aromatic amino acids 1000 times faster. In an attempt to discover the critical residues for this differential substrate specificity, the aspartate aminotransferase mutant V39L has recently been prepared. It showed improved Kcat/Km values for aspartate, glutamate and tyrosine and the corresponding oxo acids, mainly due to two to ten times lower Km values. For example, the Km values of V39L (wild type) for Asp and Glu are 0.12 (1.0) and 0.85 (2.7) mM respectively. The mutant was co-crystallized with 30 mM maleate from both polyethylene glycol and ammonium sulfate. Both structures were solved and refined to R-factors of 0.22 and 0.20 at 2.85 and 2.5 A resolution respectively. They bear strong resemblance to the closed structure of the wild type enzyme complexed with maleate. The unexpected feature is that, for the first time, the closed form was produced in crystals grown from ammonium sulfate. It is concluded that the mutation has shifted the conformational equilibrium towards the closed form, which leads to generally reduced substrate Kms.
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PMID:Three-dimensional structure of a mutant E. coli aspartate aminotransferase with increased enzymic activity. 807 30

A relationship between plasma membrane fatty acid binding protein (FABPpm), a putative membrane transporter for long-chain fatty acids, and the mitochondrial isoform of aspartate aminotransferase (m-AspAT) has been reported. Accordingly, we have compared the chemical and immunological properties of rat liver m-AspAT with those of rat liver FABPpm isolated by two procedures: 1) detergent solubilization of the membranes followed by purification via fatty acid affinity chromatography (FABP-1) or 2) salt extraction of the membranes and subsequent purification by high-performance liquid chromatography (HPLC; FABP-2). Comparison of the three protein preparations revealed no differences with respect to NH2-terminal amino acid sequence, amino acid composition, peptides from tryptic digests, AspAT enzymatic activity, isoelectric point, mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), retention on five different HPLC columns, and immunoprecipitation and immunoblotting of SDS-PAGE separated proteins with polyclonal antisera. Examination of the proteins by nondenaturing PAGE showed a consistent second band in FABP-1 and FABP-2 not always present in m-AspAT. However, whenever present, this band was immunoreactive with antibodies to both m-AspAT and FABP-1. Hence, FABP-1 and FABP-2 are indistinguishable from one another. They are also at least closely related, if not identical, to m-AspAT.
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PMID:Comparison of plasma membrane FABP and mitochondrial isoform of aspartate aminotransferase from rat liver. 823 19


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