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

A soybean leaf cDNA clone, pSAT2, was isolated by hybridization to a carrot aspartate aminotransferase (EC 2.6.1.1.; AAT) cDNA clone at low stringency. pSAT2 contained an open reading frame encoding a 47640 Da protein. The protein encoded by pSAT2 showed significant sequence similarity to AAT proteins from both plants and animals. It was most similar to two Panicum mitochondrial AATs, 81.5% and 82.0% identity. Alignment of the pSAT2-encoded protein with other mature AAT enzymes revealed a 25 amino acid N-terminal extension with characteristics of a mitochondrial transit peptide. A plasmid, pEXAT2, was constructed to encode the mature pSAT2 protein lacking the putative mitochondrial transit peptide. Escherichia coli containing the plasmid expressed a functional AAT isozyme which comigrated with the soybean AAT4 isozyme during agarose gel electrophoresis. Equilibrium sucrose gradient sedimentation of soybean extracts demonstrated that AAT4 specifically cofractionated with mitochondria. Antibodies raised against the pEXAT2-encoded AAT protein reacted with AAT4 of soybean and not with other AAT isozymes detected in soybean tissues, providing further evidence that clone pSAT2 encodes the soybean mitochondrial isozyme AAT4.
Plant Mol Biol 1995 Mar
PMID:Characterization of a soybean cDNA clone encoding the mitochondrial isozyme of aspartate aminotransferase, AAT4. 776 91

A clone encoding aspartate aminotransferase (AAT, EC 2.6.1.1) was isolated from an Arabidopsis thaliana leaf cDNA library. This clone contains a 1365 bp open reading frame encoding a polypeptide of 49.8 kDa, designated Ataat1. The clone was shown to contain a chloroplastic isoenzyme as an in organellar protein import assay demonstrated that a radiolabelled transcription/translation product of 49.8 kDa was imported into viable pea chloroplasts and was subsequently processed to yield a mature protein of 45 kDa. The open reading frame corresponding to the predicted mature AAT was manipulated into an expression construct (pEC14). Transformed Escherichia coli cells containing pEC14 expressed up to 16 times more AAT activity than vector only controls, thus demonstrating conclusively that the clone encoded AAT.
Plant Mol Biol 1995 Mar
PMID:Isolation, characterisation and expression of a cDNA clone encoding plastid aspartate aminotransferase from Arabidopsis thaliana. 776 5

Aspartate aminotransferase isoenzymes are located in both the cytosol and organelles of eukaryotes, but all are encoded in the nuclear genome. In the work described here, a phylogenetic analysis was made of aspartate aminotransferases from plants, animals, yeast, and a number of bacteria. This analysis suggested that five distinct branches are present in the aspartate aminotransferase tree. Mitochondrial forms of the enzyme form one distinct group, bacterial aspartate aminotransferase formed another, and the plant and vertebrate cytosolic isoenzymes each formed a distinct group. Plant cytosolic isozymes formed a further group of which the plastid sequences were a member. The yeast mitochondrial and cytosolic aspartate aminotransferases formed groups separate from other members of the family.
J Mol Evol 1995 Apr
PMID:Evolutionary analysis of aspartate aminotransferases. 776 21

Two refined structures, differing in alkali metal ion content, of the bifunctional, pyridoxal phosphate-dependent enzyme dialkylglycine decarboxylase (DGD) are presented in detail. The enzyme is an alpha 4 tetramer, built up as a dimer of dimers, with a subunit molecular mass of 46.5 kDa. The fold of DGD is similar to those of aspartate aminotransferase, omega-amino acid aminotransferase and tyrosine phenol-lyase. The structure has two binding sites for alkali metal ions. DGD with potassium in site 1 (near the active site) and sodium in site 2 (at the surface of the molecule) has been refined against 2.6A resolution data (R-factor = 17.6%), and DGD with sodium at both sites has been refined against 2.1 A resolution data (R-factor = 17.8%). The proximity of site 1 to the active site accounts for the dependence of enzyme activity on potassium ions, and the observed active site structural changes caused by ion exchange at this site explain the inhibition of activity by sodium. DGD catalyzes both the decarboxylation of dialkylglycine species and the transamination of L-amino acids in its normal catalytic cycle. The active site structure of DGD is moderately homologous to that of aspartate aminotransferase, which catalyzes only transamination; both the differences and similarities provide mechanistic guidelines for the DGD-catalyzed reactions. Models of the L-isovaline and L-alanine external aldimine intermediates suggest mechanisms by which the decarboxylation and transamination reactions could be accomplished within the single active site. Decarboxylation is proposed to be at least partially catalyzed by stereoelectronic activation of the C alpha-carboxylate bond achieved by orienting this bond perpendicular to the plane of the pyridinium ring in the dialkylglycine external aldimine intermediate. Transamination is proposed to be catalyzed by a similar effect on the C alpha-H bond of the L-amino acid external aldimine intermediate, combined with general base catalysis provided by Lys272, in analogy to the mechanism of aspartate aminotransferase.
J Mol Biol 1995 Jan 13
PMID:Structural and mechanistic analysis of two refined crystal structures of the pyridoxal phosphate-dependent enzyme dialkylglycine decarboxylase. 779 33

We have placed two different penicillin structural genes from Aspergillus nidulans, ipnA (encoding isopenicillin N synthetase, IPNS) and acyA (encoding acyl-CoA:6-aminopenicillanic acid acyltransferase, AAT), under the control of the strong alcA promoter [alcA(p)]. Single copies of these transcriptional fusions were targeted to the same chromosomal location and conditions have been worked out which simultaneously allow induction of the alcA(p) and support penicillin biosynthesis. Transcriptional induction of the chimeric genes alcA(p)::ipnA or alcA(p)::acyA(cdna) in the relevant recombinant strains results in 10-fold higher levels of the ipnA or acyA transcripts than those resulting from transcription of the corresponding endogenous genes. This increase causes a 40-fold rise in IPNS activity or a 8-fold rise in AAT activity. Despite this rise in enzyme levels, forced expression of the ipnA gene results in only a modest increase in levels of exported penicillin, whereas forced expression of the acyA gene reduces penicillin production, showing that neither of these enzymes is rate-limiting for penicillin biosynthesis in A. nidulans. A genomic version of the alcA(p)::acyA fusion in which the acyA gene is interrupted by three small introns, is inducible by threonine to a lesser extent (as determined by both acyA mRNA levels and AAT enzyme levels) than the corresponding cDNA version, suggesting that processing of the introns present in the primary transcript may limit acyA expression.
Mol Gen Genet 1995 Jan 06
PMID:Overexpression of two penicillin structural genes in Aspergillus nidulans. 782 6

The C57BL/10 SPS/sps mouse mutant are audiogenic seizure-susceptible. The enzymatic activities of glutamate decarboxylase (GAD), GABA aminotransferase (GABA-T), alanine aminotransferase (ALA-T), aspartate aminotransferase (ASP-T), and glutamate dehydrogenase (GDH) of whole brain supernatant are significantly reduced in these epileptic mice. GABA uptake is decreased in cortex, midbrain, and pons medulla. Previous studies showed the presence of two sodium-dependent GLU uptake systems in normal (SPS/SP) mice. Glutamate Umax by System 1 is significantly decreased in these mice, whereas the Umax value for System 2 is significantly increased in the epileptic mice.
Mol Neurobiol
PMID:Altered GABAergic and glutamatergic transmission in audiogenic seizure-susceptible mice. 788 3

The crystal structure of chicken cytosolic aspartate aminotransferase (cAATase; EC 2.6.1.1) has been solved and refined at 1.9 A resolution. Orthorhombic crystals, space group P2(1)2(1)2(1), a = 56.4 A, b = 126.0 A and c = 142.3 A, were grown from polyethylene glycol solutions in the presence of maleate, a dicarboxylic inhibitor that forms a Michaelis-like complex. The pyridoxal form of the enzyme was used for crystallization. Diffraction data were collected using synchrotron radiation. The structure of the new orthorhombic crystal form was solved by molecular replacement using the partially refined 2.8 A resolution structure of the high-salt crystal form as a search model. The final value of the crystallographic R-factor after rigid body and restrained least-squares refinement is 0.175 with very good model geometry. The two 2-fold-related subunits of cAATase have distinct environments in the crystal lattice. Domain movement is strictly hindered by the lattice contacts in one subunit, while the second one possesses conformational freedom. Despite their different environments, both subunits were found in the closed conformation with one maleate molecule tightly bound in each active site. The present study allows a detailed comparison of the highly refined structures of the aspartate aminotransferase isozymes, and thus provide better insight into the role of conserved and variable residues in substrate recognition and catalysis.
J Mol Biol 1995 Mar 17
PMID:Crystal structure of the closed form of chicken cytosolic aspartate aminotransferase at 1.9 A resolution. 789 55

Despite the extensive search for disease causing mutations in exons 28-36 of the neurofibromatosis type 1 (NF1) gene, the NF1 specific mutations so far documented account for only a small proportion of all NF1 cases. In this study, we have used 8 sets of new primers to amplify sequences throughout the NF1 gene, including 10 different exons and their flanking intron sequences. The derived PCR products from 150 independent NF1 patients and 50 normal controls were examined by heteroduplex analysis on Hydrolink gels. Three novel mutations were identified and characterised. Two of these mutations include the same 3-bp deletion (AAT) within exon 17 with a silent codon change from ACA (threonine) to ACG (threonine) and a loss of the codon ATG (methionine). The third mutation is a 10-bp deletion (TTCTCTTGGA) within exon 44 resulting in the formation of an inappropriate stop codon. These results should be useful for the further elucidation of the molecular basis of NF1.
Hum Mol Genet 1993 Nov
PMID:Neurofibromatosis type 1 (NF1): the search for mutations by PCR-heteroduplex analysis on Hydrolink gels. 790 9

Hepatic and renal subacute toxicity induced by the antineoplastic drugs chlorambucil, cisplatin, epirubicin and methotrexate and the steroid alkylating agent 3 beta-hydroxy-13 alpha-amino-13,17-seco-5 alpha-androstan-17-oic-13, 17-lactam (p-[bis(2-chloroethyl) amino] phenyl) acetate was investigated in rats using serum biochemical parameters. Toxicological evaluation was performed in serum samples following the administration of dose regimens of the agents that were previously shown to be effective in suppressing malignant tumor growth or to prolong survival in tumor bearing animals. Hepatic and renal subacute toxicity was evaluated by measuring enzyme activity or concentrations of: alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, total cholesterol, gamma-glutamyltransferase, glucose, potassium, sodium, blood urea nitrogen and uric acid. The use of the above serum biochemical parameters indicated that the overall toxicity impact of the antitumor drugs was methotrexate < cisplatin < epirubicin < chlorambucil. The homo-azasteroid ester only transiently affected the biochemical parameters associated with renal toxicity, while it affected some of the biochemical parameters associated with hepatic toxicity, though to a significantly lower extent than the antitumor drugs.
Biochem Mol Biol Int 1993 Nov
PMID:Evaluation of kidney and liver subacute toxicity of antitumor agents using serum biochemical parameters in rats. 790 82

The objective was to determine the effects of persistent obesity on amino acid enzymes in white (WAT) and brown (BAT) adipose tissues. Dietary obesity was induced by feeding a cafeteria diet ad libitum for 3 months, then it was removed and the obese animals received the same diet as controls for 5 months. Dietary-induced obesity was persistent as obese rats showed a stable, higher body weight than controls (26%). Key enzymes of alpha-amino nitrogen metabolism were studied and results showed reduced activities in obese rats: glutamine synthetase (45%), AMP deaminase (52%), alanine aminotransferase (66%) and glutamate dehydrogenase (68%) in BAT, whereas WAT of obese animals only showed lower aspartate aminotransferase activity (47%) with respect to the controls. We can conclude that these adaptations in amino acid metabolism were exclusively dependent on the obese status as they were observed in an obesity model in which obese rats eat the same diet as controls.
Biochem Mol Biol Int 1994 Apr
PMID:Brown and white adipose tissue adaptive enzymatic changes on amino acid metabolism in persistent dietary-obese rats. 791 90


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