Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P80404 (GABA transaminase)
 786 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of different treatments on amino acid levels in neostriatum was studied to throw some light on the synthesis and metabolism of gamma-aminobutyric acid (GABA). Irreversible inhibition of GABA transaminase by microinjection of gamma-vinyl GABA (GVG) led to a decrease in aspartate, glutamate, and glutamine levels and an increase in the GABA level, such that the nitrogen pool remained constant. The results indicate that a large part of brain glutamine is derived from GABA. Hypoglycemia led to an increase in the aspartate level and a decrease in glutamate, glutamine, and GABA levels. The total amino acid pool was decreased compared with amino acid levels in normoglycemic rats. GVG treatment of hypoglycemic rats led to a decrease in the aspartate level and a further reduction in glutamate and glutamine levels. In this case, GABA accumulation continued, although the glutamine pool was almost depleted. The GABA level increased postmortem, but there were no detectable changes in levels of the other amino acids. Pretreatment of the rats with hypoglycemia reduced both glutamate and glutamine levels with a subsequent decreased postmortem GABA accumulation. The half-maximal GABA synthesis rate was obtained when the glutamate level was reduced by 50% and the glutamine level was reduced by 80%.
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PMID:Regulation of transmitter gamma-aminobutyric acid (GABA) synthesis and metabolism illustrated by the effect of gamma-vinyl GABA and hypoglycemia. 289 10

A gene encoding a putative GABA aminotransferase (ugatA) was isolated from the basidiomycete Ustilago maydis via heterologous hybridization to the GABA aminotransferase gene (gatA) of Aspergillus nidulans . The derived amino-acid sequence of ugatA shows strong identity throughout the protein to the GABA aminotransferase enzymes from A. nidulans and Saccharomyces cerevisiae. Northern analysis in U. maydis indicated that the ugatA transcript is inducible by the omega-amino acids GABA and beta-alanine, and is not subject to nitrogen catabolite repression. With the use of ugatA promoter-lacZ fusion constructs, it was demonstrated that the removal of sequences located approximately 250 bp 5' to the translational start site of ugatA (including multiple copies of a 7-bp direct repeat) resulted in the loss of induction by omega-amino acids. While the ugatA gene under the control of the A. nidulans gatA promoter was able to fully complement a gatA- phenotype in A. nidulans, the full-length ugatA gene was not, suggesting a lack of expression from the U. maydis promoter in A. nidulans. A U. maydis strain with a gene disruption at the ugatA locus showed decreased growth on beta-alanine as a sole nitrogen source, but was able to grow on GABA as a sole nitrogen source, indicating an alternative pathway for the utilization of GABA in U. maydis.
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PMID:Characterization of the ugatA gene of Ustilago maydis, isolated by homology to the gatA gene of Aspergillus nidulans. 859 57

Gamma-aminobutyric acid (GABA), a four-carbon non-protein amino acid, is a significant component of the free amino acid pool in most prokaryotic and eukaryotic organisms. In plants, stress initiates a signal-transduction pathway, in which increased cytosolic Ca2+ activates Ca2+/calmodulin-dependent glutamate decarboxylase activity and GABA synthesis. Elevated H+ and substrate levels can also stimulate glutamate decarboxylase activity. GABA accumulation probably is mediated primarily by glutamate decarboxylase. However, more information is needed concerning the control of the catabolic mitochondrial enzymes (GABA transaminase and succinic semialdehyde dehydrogenase) and the intracellular and intercellular transport of GABA. Experimental evidence supports the involvement of GABA synthesis in pH regulation, nitrogen storage, plant development and defence, as well as a compatible osmolyte and an alternative pathway for glutamate utilization. There is a need to identify the genes of enzymes involved in GABA metabolism, and to generate mutants with which to elucidate the physiological function(s) of GABA in plants.
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PMID:Metabolism and functions of gamma-aminobutyric acid. 1052 26

The ultimate objective of PhIMED, in which two European (Germany, Italy) and two Mediterranean (Morocco, Egypt) countries collaborate, is to improve the cultivation of French bean (Phaseolus vulgaris) under arid and semi-arid conditions by analysing and enhancing stress tolerance of the nitrogen fixing rhizobial microsymbionts. Rhizobial strains nodulating P. vulgaris (RP strains) isolated from areas in Morocco frequently subjected to drought were analysed for their salt and pH tolerance and their phylogenetic relationship. Strain RP163, exhibiting high nodulation efficiency and a broad pH tolerance was mutagenised by Tn5 and mutants unable to grow on extreme pH media were isolated. Some of the mutants affected in low pH tolerance were found to be mutated in genes related to cobalmin biosynthesis and in succinate dehydrogenase (sdhA). In a parallel approach, promoters and genes inducible under extreme pH values were identified in Rhizobium leguminosarum bv. viciae VF39, among them gabT, which encodes the GABA transaminase and which is induced under acidic conditions. The same gene is present and similarly regulated in RP163. The actSR gene region was cloned from VF39, sequenced and mutants generated in this region were found to be impaired in growth at low pH, but also under neutral conditions. The Agrobacterium rhizogenes 'promintron' promoter, reported to be activated in stationary phase, was found to be also strongly induced under acidic conditions in rhizobia and it is currently being characterised to construct a system allowing the expression of stress tolerance genes in bacteroids and free-living bacteria.
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PMID:Characterisation of Phaseolus symbionts isolated from Mediterranean soils and analysis of genetic factors related to pH tolerance. 1156 93

A Rhizobium leguminosarum bv. viciae VF39 gene (gabT) encoding a gamma-aminobutyrate (GABA) aminotransferase was identified, cloned and characterized. This gene is thought to be involved in GABA metabolism via the GABA shunt pathway, a theoretical bypass of the 2-oxoglutarate dehydrogenase complex. Mutants in gabT are still able to grow on GABA as a sole carbon and nitrogen source. 2-oxoglutarate-dependent GABA aminotransferase activity is absent in these mutants, while pyruvate-dependent activity remains unaffected. This indicates that at least two enzymes with different substrate specifities are involved in the GABA metabolism of R. leguminosarum bv. viciae VF39. The gabT promoter was cloned into a newly constructed, stable promoter-probe vector pJP2, suitable for the study of transcriptional GUS fusions in free-living bacteria and during symbiosis. Under free-living conditions the gabT promoter is induced by GABA and repressed by succinate. Transcriptional regulation is mediated by GabR in a repressor-like manner. During symbiosis with the pea host plant gabT is induced and highly expressed in the symbiotic zone. Nodules induced by gabT mutants, however, are still effective in nitrogen fixation.
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PMID:The Rhizobium leguminosarum bv. viciae VF39 gamma-aminobutyrate (GABA) aminotransferase gene (gabT) is induced by GABA and highly expressed in bacteroids. 1183 24

The growth of the biotrophic pathogen Cladosporium fulvum within the tomato (Lycopersicon esculentum Mill.) leaf is restricted to the intercellular space. Previous studies from this laboratory have demonstrated that gamma-aminobutyric acid (GABA) accumulates to millimolar concentrations in the apoplast during a compatible interaction. We decided to further investigate the role of GABA during infection. A gene encoding a required enzyme for GABA metabolism, GABA transaminase (Gat1), was cloned and sequenced from C. fulvum. The predicted protein sequence of Gat1 had high homology to other fungal GABA transaminases, particularly from Aspergillus nidulans. In vitro expression experiments revealed Gat1 to be strongly expressed during fungal growth on both GABA and glutamate whereas nearly no expression was evident during nitrogen starvation conditions. Expression of Gat1 was also apparent during infection, suggesting for the first time that C. fulvum actively metabolises GABA during infection. This indicates that the fungus may be utilising the GABA in the apoplast as a nutrient source. Further analysis revealed that the expression of tomato glutamate decarboxylase, the enzyme responsible for GABA synthesis, appeared appreciably higher during a compatible interaction than in the incompatible interaction. These findings imply that the infecting fungus may alter the physiology of the tomato leaf with the result that a source of nitrogen is supplied.
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PMID:Evidence that gamma-aminobutyric acid is a major nitrogen source during Cladosporium fulvum infection of tomato. 1185 46

Sake yeasts take up gamma-aminobutyric acid (GABA) derived from rice-koji in the primary stage of sake brewing. The GABA content in sake brewed with the UGA1 disruptant, which lacked GABA transaminase, was higher than that brewed with the wild-type strain K701. The UGA1 disruptant derived from sake yeast could not grow on a medium with GABA as the sole nitrogen source. We have isolated the sake yeast mutants of K701 that were unable to grow on a medium containing GABA as the sole nitrogen source. The growth defect of GAB7-1 and GAB7-2 mutants on GABA plates was complemented by UGA1, which encodes GABA transaminase, and UGA2, which encodes succinic semialdehyde dehydrogenase (SSADH), respectively. DNA sequence analysis revealed that GAB7-1 had a homozygous nonsense mutation in UGA1 and GAB7-2 had a heterozygous mutation (G247D) in UGA2. The GABA transaminase activity of GAB7-1 and the SSADH activity of GAB7-2 were markedly lower than those of K701. These GAB mutants displayed a higher intracellular GABA content. The GABA contents in sake brewed with the mutants GAB7-1 and GAB7-2 were 2.0 and 2.1 times higher, respectively, than that brewed with the wild-type strain K701. These results suggest that the reduced function of the GABA utilization pathway increases the GABA content in sake.
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PMID:Isolation and characterization of sake yeast mutants deficient in gamma-aminobutyric acid utilization in sake brewing. 1623 52

During germination the chestnut (Castanea sativa L.) var ecotype 33 accumulates a large amount of asparagine in the cotyledons. This compound also accumulates in the growing axis:shoots and roots. In the cotyledons, gamma-aminobutyrate (GABA) represents a major amino compound during germination and early seedling growth. In young seedlings, 35 days old, arginine predominates over the other soluble amino acids, particularly in roots. Five enzymic activities involved in arginine and GABA have been measured in the storage organ of the seed: arginase and ornithine carbamyltransferase decrease during germination indicating the slowing down of the urea cycle. In contrast, ornithine aminotransferase increases. Glutamate decarboxylase is particularly active about 21 days after imbibition and GABA aminotransferase activity decreases during germination. These two activities are in good agreement with the likely transport of GABA from cotyledons to growing axis. Asparagine, arginine, and GABA are the three amino compounds obviously involved in the mobilization of nitrogen reserves in the germinating chestnut seeds Castanea sativa.
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PMID:Amino Acids Content in Germinating Seeds and Seedlings from Castanea sativa L. 1666 82

Pea plants incubated in 15N2 rapidly accumulated labeled gamma-aminobutyrate (GABA) in the plant cytosol and in bacteroids of Rhizobium leguminosarum bv. viciae 3841. Two pathways of GABA metabolism were identified in R. leguminosarum 3841. In the first, glutamate is formed by GABA aminotransferase (GabT), transferring the amino group from GABA to 2-oxoglutarate. In the second, alanine is formed by two omega-aminotransferases (OpaA and OpaB), transferring the amino group from GABA to pyruvate. While the gabT mutant and the gabT opaA double mutant grew on GABA as a nitrogen source, the final triple mutant did not. The semialdehyde released from GABA by transamination is oxidized by succinate semialdehyde dehydrogenase (GabD). Five of six potential GabD proteins in R. leguminosarum bv. viciae 3841 (GabD1, -D2, -D3, -D4, and -D5) were shown by expression analysis to have this activity. However, only mutations of GabD1, GabD2, and GabD4 were required to prevent utilization of GABA as the sole nitrogen source in culture. The specific enzyme activities of GabT, Opa, and GabD were highly elevated in bacteroids relative to cultured bacteria. This was due to elevated expression of gabT, opaA, gabD1, and gabD2 in nodules. Strains mutated in aminotransferase and succinate semialdehyde dehydrogenases (gabT, opaA, or opaB and gabD1, gabD2, or gabD4, respectively) that cannot use GABA in culture still fixed nitrogen on plants. While GABA catabolism alone is not essential for N2 fixation in bacteroids, it may have a role in energy generation and in bypassing the decarboxylating arm of the tricarboxylic acid cycle.
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PMID:Pathway of gamma-aminobutyrate metabolism in Rhizobium leguminosarum 3841 and its role in symbiosis. 1918 99

The gamma-aminobutyrate (GABA) shunt, an alternative route for the conversion of alpha-ketoglutarate to succinate, involves the glutamate decarboxylase Gad1p, the GABA transaminase Uga1p and the succinate semialdehyde dehydrogenase Uga2p. This pathway has been extensively described in plants and animals, but its function in yeast remains unclear. We show that the flux through Gad1p is insignificant during fermentation in rich sugar-containing medium, excluding a role for this pathway in redox homeostasis under anaerobic conditions or sugar stress. However, we found that up to 4 g of exogenous GABA/liter was efficiently consumed by yeast. We studied the fate of this consumed GABA. Most was converted into succinate, with a reaction yield of 0.7 mol/mol. We also showed that a large proportion of GABA was stored within cells, indicating a possible role for this molecule in stress tolerance mechanisms or nitrogen storage. Furthermore, based on enzymatic and metabolic evidence, we identified an alternative route for GABA catabolism, involving the reduction of succinate-semialdehyde into gamma-hydroxybutyric acid and the polymerization of gamma-hydroxybutyric acid to form poly-(3-hydroxybutyric acid-co-4-hydroxybutyric acid). This study provides the first demonstration of a native route for the formation of this polymer in yeast. Our findings shed new light on the GABA pathway and open up new opportunities for industrial applications.
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PMID:New insights into {gamma}-aminobutyric acid catabolism: Evidence for {gamma}-hydroxybutyric acid and polyhydroxybutyrate synthesis in Saccharomyces cerevisiae. 1941 12


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