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)

Five aspartate aminotransferase (EC 2.6.1.1; AAT) isozymes were identified in soybean seedling extracts and designated AAT1 to AAT5 based on their rate of migration on non-denaturing electrophoretic gels. AAT1 was detected only in extracts of cotyledons from dark-grown seedlings. AAT3 and AAT4 were detected in crude extracts of leaves and in cotyledons of seedlings grown in the light. AAT2 and AAT5 were detected in all tissues examined. A soybean leaf cDNA clone, pSAT17, was identified by hybridization to a carrot AAT cDNA clone at low stringency. pSAT17 had an open reading frame which could encode a 50,581 Da protein. Alignment of the deduced amino acid sequence from the pSAT17 open reading frame with mature AAT protein sequences from rat disclosed a 60 amino acid N-terminal extension in the pSAT17 protein. This extension had characteristics of a plastid transit peptide. A plasmid, pEXAT17, was constructed which encoded the mature protein lacking the putative chloroplast transit polypeptide. Transformed Escherichia coli expressed a functional soybean AAT isozyme, which comigrated with the soybean AAT5 isozyme during agarose gel electrophoresis. Differential sucrose gradient sedimentation of soybean extracts indicated that AAT5 specifically cofractionated with chloroplasts. Antibodies raised against the pEXAT17-encoded AAT protein specifically reacted with the AAT5 isozyme of soybean and not with any of the other isozymes, indicating that the soybean cDNA clone, pSAT17, encodes the chloroplast isozyme, AAT5.
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PMID:Isolation and characterization of a soybean cDNA clone encoding the plastid form of aspartate aminotransferase. 768 17

Here, a complete study is described of all the genes and isoenzymes for aspartate aminotransferase (AspAT) present in Arabidopsis thaliana. Four classes of cDNAs representing four distinct AspAT genes (ASP1-ASP4) have been cloned from Arabidopsis. Sequence analysis of the cDNAs suggests that the encoded proteins are targeted to different subcellular compartments. ASP1 encodes a mitochondrial form of AspAT, ASP3 encodes a chloroplastic/plastidic form of AspAT, whereas ASP2 and ASP4 each encode cytosolic forms of AspAT. Three distinct AspAT holoenzymes (AAT1-AAT3) were resolved by activity gel analysis. Organelle isolation reveals that AAT1 is mitochondrial-localized, AAT3 is plastid-localized, and AAT2 is cytosolic. Gene-specific Northern analysis reveals that each Asp mRNA accumulates differentially with respect to organ-type. However, the individual Asp mRNAs show no dramatic fluctuations in response to environmental stimuli such as light. Southern analysis reveals that four distinct nuclear genes probably represent the entire AspAT gene family in Arabidopsis. These molecular studies shed light on the subcellular synthesis of aspartate in Arabidopsis and suggest that some of the AspAT isoenzymes may play overlapping roles in plant nitrogen metabolism.
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PMID:The aspartate aminotransferase gene family of Arabidopsis encodes isoenzymes localized to three distinct subcellular compartments. 789 12

Arabidopsis contains five isoenzymes of aspartate aminotransferase (AspAT) localized to the cytosol, chloroplast, mitochondria, or peroxisomes. To define the in vivo function of individual isoenzymes, we screened for Arabidopsis mutants deficient in either of the two major isoenzymes, cytosolic AAT2 or chloroplastic AAT3, using a native gel activity assay. In a screen of 8,000 M2 seedlings, three independent mutants deficient in cytosolic AAT2 (aat2) and two independent mutants deficient in chloroplastic AAT3 (aat3) were isolated. Mapping of aat2 and aat3 mutations and the five AspAT genes (ASP1-ASP5) established associations as follows: the mutation affecting aat2 maps with and cosegregates with ASP2, one of two expressed genes for cytosolic AspAT; the mutation affecting aat3 maps to the same location as the ASP5 gene encoding chloroplastic AspAT. Phenotypic analysis of the aat2 and aat3 mutants revealed a dramatic aspartate-related phenotype in one of the mutants deficient in cytosolic AAT2. The aat2-2 mutant displays an 80% reduction in levels of aspartate transported in the phloem of light-grown plants, and a 50% reduction in levels of asparagine transported in dark-adapted plants. These results indicate that cytosolic AAT2 is the major isoenzyme controlling aspartate synthesized for nitrogen transport in the light, and that this aspartate pool is converted to asparagine when plants are dark adapted.
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PMID:Arabidopsis mutants define an in vivo role for isoenzymes of aspartate aminotransferase in plant nitrogen assimilation. 961 Nov 68

A soybean cDNA clone, pSAT1, which encodes both the cytosolic and glyoxysomal isozymes of aspartate aminotransferase (AAT; EC 2.6.1.1) was isolated. Genomic Southern blots and analysis of genomic clones indicated pSAT1 was encoded by a single copy gene. pSAT1 contained an open reading frame with ca. 90% amino acid identity to alfalfa and lupin cytosolic AAT and two in-frame start codons, designated ATG1 and ATG2. Alignment of this protein with other plant cytosolic AAT isozymes revealed a 37 amino acid N-terminal extension with characteristics of a peroxisomal targeting signal, designated PTS2, including the modified consensus sequence RL-X5-HF. The second start codon ATG2 aligned with previously reported start codons for plant cytosolic AAT cDNAs. Plasmids constructed to express the open reading frame initiated by each of the putative start codons produced proteins with AAT activity in Escherichia coli. Immune serum raised against the pSAT1-encoded protein reacted with three soybean AAT isozymes, AAT1 (glyoxysomal), AAT2 (cytosolic), and AAT3 (subcellular location unknown). We propose the glyoxysomal isozyme AAT1 is produced by translational initiation from ATG1 and the cytosolic isozyme AAT2 is produced by translational initiation from ATG2. N-terminal sequencing of purified AAT1 revealed complete identity with the pSAT1-encoded protein and was consistent with the processing of the PTS2. Analysis of cytosolic AAT genomic sequences from several other plant species revealed conservation of the two in-frame start codons and the PTS2 sequence, suggesting that these other species may utilize a single gene to generate both cytosolic and glyoxysomal or peroxisomal forms of AAT.
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PMID:Characterization of a single soybean cDNA encoding cytosolic and glyoxysomal isozymes of aspartate aminotransferase. 962 Feb 68