Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.6.1.1 (aspartate aminotransferase)
21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Arabidopsis mutants deficient in cytosolic (AAT2) or chloroplastic (AAT3) aspartate (Asp) aminotransferase were characterized at the molecular and physiological levels. All of the ethyl methane sulfonate- or nitrosomethylurea-generated mutants are missense mutations, as determined by sequencing of the ASP2 gene from the cytosolic aat2 mutants (aat2-1, aat2-2, aat2-4, and aat2-5) and the ASP5 gene from the chloroplastic aat3 mutants (aat3-1, aat3-2, and aat3-4). A T-DNA insertion mutant in cytosolic AAT2 (aat2-T) was also identified. All the cytosolic aat2 and chloroplastic aat3 mutants have less than 6% AAT2 and less than 3% AAT3 activity, respectively, as determined by the native gel assay; however, none are nulls. The metabolic and physiological affect of these mutations in AAT isoenzymes was determined by measuring growth and amino acid levels in the aat mutants. Two aat2 mutants (aat2-2 and aat2-T) show reduced root length on Murashige and Skoog medium. For aat2-2, this growth defect is exaggerated by Asp supplementation, suggesting a defect in Asp metabolism. Amino acid analysis of the aat mutants showed alterations in levels of Asp and/or Asp-derived amino acids in several aat2 alleles. Two aat2 mutants show dramatic decreases in Asp and asparagine levels in leaves and/or siliques. As such, the cytosolic AAT2 isoenzyme appears to serve a nonredundant function in plant nitrogen metabolism of Asp and Asp-derived amino acids.
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PMID:Molecular and physiological analysis of Arabidopsis mutants defective in cytosolic or chloroplastic aspartate aminotransferase. 1206 9

Nitrogen assimilation is a vital process controlling plant growth and development. Inorganic nitrogen is assimilated into the amino acids glutamine, glutamate, asparagine, and aspartate, which serve as important nitrogen carriers in plants. The enzymes glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), aspartate aminotransferase (AspAT), and asparagine synthetase (AS) are responsible for the biosynthesis of these nitrogen-carrying amino acids. Biochemical studies have revealed the existence of multiple isoenzymes for each of these enzymes. Recent molecular analyses demonstrate that each enzyme is encoded by a gene family wherein individual members encode distinct isoenzymes that are differentially regulated by environmental stimuli, metabolic control, developmental control, and tissue/cell-type specificity. We review the recent progress in using molecular-genetic approaches to delineate the regulatory mechanisms controlling nitrogen assimilation into amino acids and to define the physiological role of each isoenzyme involved in this metabolic pathway.
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PMID:THE MOLECULAR-GENETICS OF NITROGEN ASSIMILATION INTO AMINO ACIDS IN HIGHER PLANTS. 1501 1

Nitrogen (N) is an essential requirement for kernel growth in maize (Zea mays); however, little is known about how N assimilates are metabolized in young earshoots during seed development. The objective of this study was to assess amino acid metabolism in cob and spikelet tissues during the critical 2 weeks following silking. Two maize hybrids were grown in the field for 2 years at two levels of supplemental N fertilizer (0 and 168 kg N/ha). The effects of the reproductive sink on cob N metabolism were examined by comparing pollinated to unpollinated earshoots. Earshoots were sampled at 2, 8, 14, and 18 d after silking; dissected into cob, spikelet, and/or pedicel and kernel fractions; then analyzed for amino acid profiles and key enzyme activities associated with amino acid metabolism. Major amino acids in the cob were glutamine (Gln), aspartic acid (Asp), asparagine (Asn), glutamate, and alanine. Gln concentrations dropped dramatically from 2 to 14 d after silking in both pollinated and unpollinated cobs, whereas all other measured amino acids accumulated over time in unpollinated spikelets and cobs, especially Asn. N supply had a variable effect on individual amino acid levels in young cobs and spikelets, with Asn being the most notably enhanced. We found that the cob performs significant enzymatic interconversions among Gln, alanine, Asp, and Asn during early reproductive development, which may precondition the N assimilate supply for sustained kernel growth. The measured amino acid profiles and enzymatic activities suggest that the Asn to Gln ratio in cobs may be part of a signal transduction pathway involving aspartate aminotransferase, Gln synthetase, and Asn synthetase to indicate plant N status for kernel development.
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PMID:Amino acid metabolism in maize earshoots. Implications for assimilate preconditioning and nitrogen signaling. 1553 10

We have increased the contents of several amino acids in the seeds of Arabidopsis thaliana by introduction of aspartate aminotransferase (AAT), an enzyme of the aspartate biosynthetic pathway. mRNA was prepared from one-week-old seedlings of Glycine max cv. enrei and the cDNA encoding AAT5 was isolated and linked to the CaMV35S promoter in the plant vector pBI121. The AAT5 gene encodes a protein of 462 amino acid residues that shows 51% amino acid sequence similarity to A. thaliana chloroplast Asp3. The soybean AAT5 also contains a chloroplast transit peptide and is able to functionally complement a Saccharomyces cerevisiae mutant lacking the Asp5 gene. A. thaliana was transformed with the AAT5 gene from Agrobacterium tumefaciens by the vacuum infiltration method. The AAT5 gene was detected in the transcript and genomic DNA from the transgenic T2 plants. The T3 progeny showed a 3:1 segregation ratio indicating the presence of a single integration. Expression of G. max AAT5 in A. thaliana transformants caused 3-, 4-, 23-, and 50-fold increases in the contents of free glycine, alanine, asparagine, and glutamine, respectively, in the T3 seeds. A decrease in the contents of valine, tyrosine, isoleucine, leucine, and phenylalanine by several folds was also observed. Thus, it is of interest that a key gene expression resulted in marked changes of metabolites in plant seeds.
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PMID:Variation of the amino acid content of Arabidopsis seeds by expressing soybean aspartate aminotransferase gene. 1623 95

The free amino acid concentrations in cotyledons and axes of soybean (Glycine max [L.] Merr. cv. Wells) seedlings were determined by automated single column analysis after germination at 10 and 23 C. After 5 days germination at 10 C, glutamate and aspartate were in high concentration in both cotyledons and axes (38 and 24% of total free amino acids recovered, respectively), whereas the concentrations of their amide derivatives, asparagine and glutamine, were low in cotyledons (4.4%) and high in axes (21%). In contrast, after 5 days germination at 23 C, asparagine and glutamine accounted for 22 and 45% of total free amino acids in cotyledons and axes respectively, and aspartate and glutamate concentrations were low. The activities of glutamine synthetase and asparagine synthetase were considerably lower in tissues from the 10 C treatment than those from the 23 C treatment.Aspartate and glutamate concentrations were nearly equal in all but one sample. Both glutamate oxaloacetate transaminase and glutamate dehydrogenase activities were much higher in axis tissues at 23 C as compared to 10 C. Arrhenius plots of axis glutamate oxaloacetate transaminase and glutamate dehydrogenase activities were biphasic and triphasic, respectively, with energies of activation for both increasing with low temperature. Energies of activation were identical for glutamate oxaloacetate transaminase from 10 and 23 C treatments but much higher for glutamate dehydrogenase from 23 C-treated axes. This indicates a difference in enzyme complement for glutamate dehydrogenase with the two treatments.Hydrolysis of free amino acid sample (basic fraction) aliquots showed large quantities of peptides in 23 C-treated axes at 2 days, while few or no peptides were found in the 10 C treatment. Amino acid residues most prevalent in peptides were aspartate, threonine, serine, glutamate, and glycine.
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PMID:Low Temperature Effects on Soybean (Glycine max [L.] Merr. cv. Wells) Free Amino Acid Pools during Germination. 1666 May 75

In the seedcoats of developing pea seeds, the maximal activities of asparaginase (EC 3.5.1.1) and aspartate: alpha-ketoglutarate aminotransferase (EC 2.6.1.1) are attained early in development, before the embryo has expanded to fill the embryo sac. These two enzyme activities could account for the early absence of asparagine and aspartate from the fluid secreted by the seedcoats into the embryo sac.CHANGES IN THE ACTIVITIES OF ALANINE: alpha-ketoglutarate aminotransferase (EC 2.6.1.2), glutamate dehydrogenase (EC 1.4.1.3), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.13) have also been measured, in cotyledons as well as seedcoats. On a fresh weight basis, the highest activities of asparaginase and both aminotransferases developed in the seedcoats, whereas the highest activities of the remaining enzymes developed in the cotyledons.The data indicate that the amide groups of imported asparagine and glutamine are metabolized differently, largely by asparaginase and glutamate synthase, respectively. The NH(4) (+) released by the action of asparaginase is evidently reassimilated in cotyledon cells by the joint action of glutamate dehydrogenase, glutamine synthetase, and glutamate synthase. The data emphasize the central importance of alpha-ketoglutarate-glutamate cycling in the redistribution of amino groups associated with the net synthesis of amino acids and reserve proteins.
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PMID:Changes in Activities of Enzymes of Nitrogen Metabolism in Seedcoats and Cotyledons during Embryo Development in Pea Seeds. 1666 21

Amide and ureide biogenic enzymes were measured in the plant fraction of soybean (Glycine max) nodules during the period 11 to 23 days after inoculation with Rhizobium japonicum (USDA 3I1b142). Enzymes involved in the initial assimilation of ammonia, i.e. glutamine synthetase, glutamate synthase, and aspartate aminotransferase, showed substantial increases in their specific activities over the time course. These increases paralleled the induction of nitrogenase activity in the bacteroid and leghemoglobin synthesis in the plant fraction. The specific activity of asparagine synthetase, however, showed a rapid decline after an initial increase in specific activity. Following the initial increases in the ammonia assimilatory enzymes, there was an increase in the activity of 5-phosphoribosylpyrophosphate amidotransferase, the enzyme which catalyzes the first committed step of de novo purine biosynthesis. This was followed by a dramatic increase in the purine oxidative enzymes, xanthine dehydrogenase and uricase. Smaller increases were observed in the activities of enzymes associated with the supply of metabolites to the purine biosynthetic pathway: phosphoglycerate dehydrogenase, serine hydroxymethylase, and methylene tetrahydrofolate dehydrogenase.The concentration of asparagine in the plant fraction decreased at the same time as the observed decrease in asparagine synthetase activity. This was followed by a recovery in plant fraction levels of asparagine in the presence of a continuing fall in the glutamine concentration and continued low asparagine synthetase activity.The data presented are consistent with initial assimilation of ammonia into glutamine and aspartate, which are metabolized by an elevation of endogenous purine biosynthetic enzymes, and then, by the induction of a specific group of purine oxidative enzymes, directed to allantoic acid production.
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PMID:Enzymes of amide and ureide biogenesis in developing soybean nodules. 1666 97

Budgets for import and utilization of ureide, amides, and a range of amino acids were constructed for the developing first-formed fruit of symbiotically dependent cowpea (Vigna unguiculata [L.] Walp. cv Vita 3). Data on fruit total N economy, and analyses of the xylem and phloem streams serving the fruit, were used to predict the input of various solutes while the compositions of the soluble and protein pools of pod, seed coat, and embryo were used to estimate the net consumption of compounds. Ureides and amides provided virtually all of the fruit's N requirements for net synthesis of amino compounds supplied inadequately from the parent plant. Xylem was the principal source of ureide to the pod, while phloem was the major source of amides to pod and seed. All fruit parts showed in vitro activity of urease (EC 3.5.1.5), allantoinase (EC 3.5.2.5), asparaginase (EC 3.5.11), ammonia-assimilating enzymes and aspartate and alanine aminotransferases (EC 2.61.1 and EC 2.6.1.1.2). Asparagine:pyruvate aminotransferase (EC 2.6.1.14) was recovered only from the pod. The pod was initially the major site for processing and incorporating N; later seed coats and finally embryos became predominant. Ureides were broken down mainly in the pod and seed coat. Amide metabolism occurred in all fruit organs, but principally in the embryo during much of seed growth. Seed coats released N to embryos mainly as histidine, arginine, glutamine, and asparagine, hardly at all as ureide. Amino compounds delivered in noticeably deficient amounts to the fruit were arginine, histidine, glycine, glutamate, and aspartate, while seeds received insufficient arginine, histidine, serine, glycine, and alanine. Quantitatively based schemes are proposed depicting the principal metabolic transformation accompanying N-flow between seed compartments during development.
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PMID:Nitrogen nutrition and metabolic interconversions of nitrogenous solutes in developing cowpea fruits. 1666 63

This study was designed to assess the relationship between mutations in the FSH receptor (FSHr) gene and polycystic ovary syndrome (PCOS) in Italian women. The study population included 50 patients with PCOS and 50 age- and body mass index (BMI)-matched controls. A complete anthropometrical, hormonal and pelvic ultrasonographic evaluation was performed in all subjects. Genomic DNA was extracted from peripheral lymphocytes and then each exon of the FSHr gene was amplified by PCR. The mutation identified was cloned and the functional properties were studied after transient expression in COS-7 cells. Direct sequencing of exons 1-10 of the FSHr gene revealed the presence of a heterozygous AAT/ATT mutation affecting the isoleucine residue at position 411, which was replaced by an asparagine, in the second transmembrane segment (I411N). This mutation was only found in one woman with PCOS and not in her parents. This mutation was not present in 50 age and BMI controls and in another 150 women not affected by PCOS. The functional study after transient expression in COS-7 cells revealed that this I411N had similar functional characteristics with respect to the wild type FSHr (wtFSHr). Genetic analyses of polymorphisms in the human FSHr gene were also performed. All 50 women with PCOS harbored the A307T polymorphic variant, 56% harbored N680S, 30% S680S and 14% N680N polymorphisms. In conclusion, the present study demonstrates that mutations of the FSHr gene are rare in Italian women. The only mutation that we found does not appear to have any pathophysiological significance in PCOS.
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PMID:Genetic analysis of the follicle stimulating hormone receptor gene in women with polycystic ovary syndrome. 1725 94

A novel human leucocyte antigen (HLA)-A33 (HLA-A*3309) allele has been identified in a Caucasian family from Middle Europe using single allele-specific sequencing strategy. This allele is identical to the HLA-B*3308 allele except for one point mutation in exon 2 at codon 66 (AAA-->AAT), resulting in an amino acid change from lysine (K) to asparagine (N).
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PMID:A novel HLA-A*33 (A*3309) allele in a Caucasian family that differs at protein position 66 from HLA-A*3308. 1755 84


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