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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two isoenzymic forms of aspartate aminotransferase are present in the plant fraction of developing lupin root nodules. One of these forms, aspartate aminotransferase-P2 (AAT-P2), increases dramatically with the onset of biological nitrogen fixation and is associated with the assimilation of ammonia by the plant in the Rhizobium-legume symbiosis. A day 18 lupin nodule cDNA library in the lambda ZapII vector was immunoscreened with a monoclonal antibody specific for AAT-P2 and yielded two near-full-length 1700 bp clones. These clones were sequenced. Amino acid sequences from three peptides derived from immunopurified AAT-P2 were aligned, and showed 100% homology with the amino acid sequence deduced from the cDNA clones. The DNA sequence showed 50% homology with AAT sequences from a range of animal sources. Conversion of the clones to the phagemid form allowed their expression in Escherichia coli where both exhibited enzyme activity that could be immunoprecipitated with AAT-P2-specific monoclonal antibodies. Western blot analysis revealed protein moieties with molecular masses of 39, 43, 45 and 55 kDa. The 5' end of the clones coded for a hydrophobic leader sequence of about 50 amino acids indicative of a targeting sequence and consistent with the plastid localisation of nodule AAT-P2.
Plant Mol Biol 1992 Jun
PMID:Molecular cloning of a cDNA encoding aspartate aminotransferase-P2 from lupin root nodules. 162 92

We have isolated an alfalfa leaf cDNA clone that encodes aspartate aminotransferase (AAT, EC 2.6.1.1) by direct complementation of an Escherichia coli aspartate auxotroph with a plasmid cDNA library. DNA sequence analysis of the recombinant plasmid, pMU1, revealed that a 1514 bp cDNA was inserted in the correct orientation and in-frame with the start of the lacZ coding sequence in the vector, pUC18. The resulting fusion protein is predicted to be 424 amino acids in length with a molecular weight of 46387 Daltons. The cDNA-encoded protein has a characteristic pyridoxal phosphate attachment site motif and has substantial amino acid sequence homology to both animal and bacterial AATs. Plasmid pMU1 encodes an AAT with a Km for aspartate of 3.3 mM, a Km for 2-oxoglutarate of 0.28 mM, and a pH optimum between 8.0 and 8.5. Several lines of evidence including Western blot analysis, the isoelectric point of the encoded protein, and the effect of pH on the activity of the fusion protein, suggest that the cDNA encodes the isozyme AAT-1 rather than AAT-2. Northern blot analysis showed that the aat-1 clone hybridized to a 1.6 kb transcript present in alfalfa leaves, roots and nodules. The relative concentrations of aat-1 mRNA in these tissues were 1:2:5, respectively. Thus, transcription of aat-1 appears to be induced during nodule development. Southern blot analysis suggested that AAT-1 in alfalfa is encoded by either a single-copy gene or a small, multigene family.
Mol Gen Genet 1991 Dec
PMID:Isolation and analysis of a cDNA clone that encodes an alfalfa (Medicago sativa) aspartate aminotransferase. 175 49

Four new crystal forms of chicken cytosolic aspartate aminotransferase have been grown from polyethylene glycol solutions. Crystals of the unliganded enzyme and of enzyme liganded with maleate diffract to 1.8 A resolution. Both the free and maleate-liganded enzymes crystallize in space group P2(1)2(1)2(1), but display slightly different cell dimensions (a = 56.9 A, b = 126.9 A and c = 124.6 A versus a = 56.5 A, b = 126.1 A and c = 124.6 A). The influence of various divalent metal ions, dioxane and non-ionic detergent beta-octylglucoside on crystallization has been investigated. The best crystals of liganded enzyme were obtained in the presence of Mg2+ ions, and these crystals were used for data collection to 1.9 A resolution.
J Mol Biol 1991 Sep 05
PMID:New crystal form of cytosolic chicken aspartate aminotransferase suitable for high-resolution X-ray analysis. 192 Apr 19

Effect of ultraviolet and gamma radiations on the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LD) in Biomphalaria alexandrina snails, the specific intermediate host of schistosomiasis, was investigated. Changes in the electrophoretic pattern of LD in the species under study were also taken as a measured parameter and the effect of gamma-irradiation on the glutathione content in the haemolymph of the snails have been included.
Cell Mol Biol 1991
PMID:Variation of transaminases and lactate dehydrogenase in irradiated Biomphalaria alexandrina snails. 193 13

Aspartate aminotransferase undergoes major shifts in the conformational equilibrium of the protein matrix during transamination. The present study defines the two conformational states of the enzyme by crystallographic analysis, examines the conditions under which the enzyme crystallizes in each of these conformations, and correlates these conditions with the conformational behaviour of the enzyme in solution, as monitored by a fluorescent reporter group. Cocrystallization of chicken mitochondrial aspartate aminotransferase with inhibitors and covalent coenzymesubstrate adducts yields three different crystal forms. Unliganded enzyme forms triclinic crystals of the open conformation, the structure of which has been solved (space group P1) [Ford, G. C., Eichele, G. & Jansonius, J. N. (1980) Proc. Natl Acad. Sci. USA 77, 2559-2563; Kirsch, J. F., Eichele, G., Ford, G. C., Vincent, M. G., Jansonius, J. N., Gehring, H. & Christen, P. (1984) J. Mol. Biol. 174, 487-525]. Complexes of the enzyme with dicarboxylate ligands form monoclinic or orthorhombic crystals of the closed conformation. The results of structure determinations of the latter two crystal forms at 0.44 nm resolution are described here. In the closed conformation, the small domain has undergone a rigid-body rotation of 12-14 which closes the active-site pocket. Shifts in the conformational equilibrium of aspartate aminotransferase in solution, as induced by substrates, substrate analogues and specific dicarboxylic inhibitors, can be monitored by changes in the relative fluoresence yield of the enzyme labelled at Cys166 with monobromotrimethylammoniobimane. The pyridoxal and pyridoxamine forms of the labelled enzyme show the same fluorescence properties, whereas in the apoenzyme the fluorescence intensity is reduced by 30%. All active-site ligands, if added to the labelled pyridoxal enzyme at saturating concentrations, cause a decrease in the fluorescence intensity by 40-70% and a blue shift of maximally 5 nm. Comparison of the fluorescence properties of the enzyme in various functional states with the crystallographic data shows that both techniques probe the same conformational equilibrium. The conformational change that closes the active site seems to be ligand-induced in the reaction of the pyridoxal form of the enzyme and syncatalytic in the reverse reaction with the pyridoxamine enzyme.
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PMID:The open/closed conformational equilibrium of aspartate aminotransferase. Studies in the crystalline state and with a fluorescent probe in solution. 200 2

The pathway construction for biosynthesis of aromatic amino acids in Escherichia coli is atypical of the phylogenetic subdivision of gram-negative bacteria to which it belongs (R. A. Jensen, Mol. Biol. Evol. 2:92-108, 1985). Related organisms possess second pathways to phenylalanine and tyrosine which depend upon the expression of a monofunctional chorismate mutase (CM-F) and cyclohexadienyl dehydratase (CDT). Some enteric bacteria, unlike E. coli, possess either CM-F or CDT. These essentially cryptic remnants of an ancestral pathway can be a latent source of biochemical potential under certain conditions. As one example of advantageous biochemical potential, the presence of CM-F in Salmonella typhimurium increases the capacity for prephenate accumulation in a tyrA auxotroph. We report the finding that a significant fraction of the latter prephenate is transaminated to L-arogenate. The tyrA19 mutant is now the organism of choice for isolation of L-arogenate, uncomplicated by the presence of other cyclohexadienyl products coaccumulated by a Neurospora crassa mutant that had previously served as the prime biological source of L-arogenate. Prephenate aminotransferase activity was not conferred by a discrete enzyme, but rather was found to be synonymous with the combined activities of aspartate aminotransferase (aspC), aromatic aminotransferase (tyrB), and branched-chain aminotransferase (ilvE). This conclusion was confirmed by results obtained with combinations of aspC-, tyrB-, and ilvE-deficient mutations in E. coli. An example of disadvantageous biochemical potential is the presence of a cryptic CDT in Klebsiella pneumoniae, where a mutant carrying multiple enzyme blocks is the standard organism used for accumulation and isolation of chorismate.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Remnants of an ancient pathway to L-phenylalanine and L-tyrosine in enteric bacteria: evolutionary implications and biotechnological impact. 208 22

Both the mouse cytosolic malate dehydrogenase gene and its mitochondrial counterpart contain eight introns, of which two are present at identical positions between the isozyme genes. The probability that the two intron positions coincide by chance between the two genes has been shown to be significantly small (= 1.3 x 10(-3), suggesting that the conservation of the intron positions has a biological significance. On the basis of a rooted phylogenetic tree inferred from a comparison of these isozymes and lactate dehydrogenases, we have shown that the origins of the conserved introns are very old, possibly going back to a date before the divergence of eubacteria, archaebacteria, and eukaryotes. In the aspartate aminotransferase isozyme genes, five of the introns are at identical places. The origins of the five conserved introns, however, are not obvious at present. It remains possible that some or all of the conserved introns have evolved after the divergence of eubacteria and eukaryotes.
J Mol Evol 1990 Sep
PMID:Compartmentalized isozyme genes and the origin of introns. 212 Apr 56

In situ hybridization histochemistry (ISHH) using synthetic oligonucleotide probes has been used to identify cells containing the mRNAs coding for glutaminase (GluT), aspartate aminotransferase (AspT) and glutamic acid decarboxylase (GAD). The distribution of GAD mRNA confirms previous descriptions and matches the distribution of GAD detected using specific antibodies. AspT mRNA is widely distributed in the brain, but is present at high levels in GABAergic neuronal populations, some that may be glutamatergic, and in a subset of neurons which do not contain significant levels of either GAD or GluT mRNA. Particularly prominent are the neurons of the magnocellular division of the red nucleus, the large cells in the deep cerebellar nuclei and the vestibular nuclei and neurons of the lateral superior olivary nucleus. GluT mRNA does not appear to be present at high levels in all GAD-containing neurons, but is seen prominently in many neuronal populations that may use glutamate as a neurotransmitter, such as neocortical and hippocampal pyramidal cells, the granule cells of the cerebellum and neurons of the dentate gyrus of the hippocampus. The heaviest labelling of GluT mRNA is seen in the lateral reticular nucleus of the medulla. ISHH using probes directed against the mRNAs encoding these enzymes may be an important technique for identifying glutamate and aspartate using neuronal populations and for examining their regulation in a variety of experimental and pathological circumstances.
Brain Res Mol Brain Res 1990 May
PMID:Distribution of messenger RNAs encoding the enzymes glutaminase, aspartate aminotransferase and glutamic acid decarboxylase in rat brain. 216 7

Crystals suitable for X-ray analysis of porcine mitochondrial aspartate aminotransferase in the closed conformation were obtained after the apoenzyme was reconstituted with N-5'-phosphopyridoxyl-L-aspartate, an inhibitor in which the cofactor is covalently bound to the substrate. This results in a crystal form that has not been encountered previously in studies of aspartate aminotransferases. The crystals belong to the trigonal space group P3121 (or the enantiomeric P3221) with unit cell dimensions alpha = b = 202.0 A, c = 58.0 A, alpha = beta = 90 degrees, gamma = 120 degrees and contain one dimer in the asymmetric unit.
J Mol Biol 1990 Oct 05
PMID:Trigonal crystals of porcine mitochondrial aspartate aminotransferase. 223 9

Hepatic ischemia induced in vivo by ligation of the left hepatic lobe of rats for up to 2 hr had no effect on cytochrome P-450, cytochrome c reductase, or lobe histology; however, cytochrome b5 increased with ischemia duration. Ethylmorphine demethylation decreased 35% after 2 hr of ischemia. Reperfusion of tissue previously made ischemic for up to 2 hr was associated with appreciable necrosis as well as decreases in cytochrome P-450, cytochrome b5, cytochrome c reductase, and ethylmorphine demethylation. Serum alanine transaminase and aspartate transaminase concentrations were increased by reperfusion of previously ischemic tissue. Reperfusion of the previously ischemic lobe for 18 hr was associated with a greater loss of cytochromes P-450 and b5, cytochrome c reductase, and ethylmorphine demethylation than reperfusion for 1 hr. The total decrease in cytochrome P-450 and b5 content was equal to the decrease in total microsomal heme content, although cytochrome P-450 decreased more than cytochrome b5. Ethoxyresorufin deethylation by hepatic microsomes from 3-methylcholanthrene-treated rats was decreased by ischemia-reperfusion; however, pentoxyresorufin dealkylation by hepatic microsomes from phenobarbital-treated rats was not, suggesting specific cytochrome P-450 isozyme loss. In vitro NADPH-dependent lipid peroxidation in hepatic microsomes from control and phenobarbital- and 3-methylcholanthrene-treated rats resulted in a selective decrease of ethoxyresorufin but not pentoxyresorufin dealkylation, similar to that observed in livers subjected to ischemia-reperfusion in vivo. These data suggest that cytochrome P-450, ethylmorphine demethylation, and ethoxyresorufin deethylation are more susceptible to ischemia-reperfusion injury than cytochrome b5 or pentoxyresorufin dealkylation.
Mol Pharmacol 1990 Dec
PMID:Effects of hepatic ischemia-reperfusion injury on the hepatic mixed function oxidase system in rats. 225 Jun 63


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