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Query: EC:1.4.1.2 (glutamate dehydrogenase)
 4,380 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have characterized Neurospora crassa transformants obtained with plasmid pJR2, which consists of the Neurospora glutamate dehydrogenase (am) gene cloned in pUC8 and an am132 host strain which contains a deletion encompassing the cloned fragment. Every one of 33 transformants tested showed extreme meiotic instability: less than 1 or 2% am+ progeny were obtained in initial or successive backcrosses between am+ transformants and am132 or in intercrosses between am+ progeny. Furthermore, am+ progeny from backcrosses gave a high proportion of auxotrophic (am) mitotic segregants during vegetative growth. These results indicate that the am+ character is not stably integrated into chromosomal DNA in any of the transformants tested. Nuclear DNAs from six transformants were analyzed by Southern hybridization. All six transformants contained sequences homologous to pJR2. Four showed restriction fragments expected for unmodified pJR2, but most showed additional bands. Southern blots of undigested DNAs showed that the plasmid sequences are present predominantly in high-molecular-weight form (larger than 20 kilobases). Southern blots showed that auxotrophic (am) progeny from a backcross to am132 had lost restriction bands corresponding to free plasmid but retained additional bands, apparently integrated into chromosomal DNA in a nonfunctional manner. Considered together, these results are most reasonably interpreted as follows: recombinant plasmids containing the am+ gene can replicate autonomously in N. crassa, the free plasmids are present in oligomeric or modified form or both, and plasmid sequences also integrate at multiple sites in the deletion host but in a nonfunctional manner. An alternate interpretation--that tandem repeats of the plasmid are integrated into chromosomal DNA but eliminated during meiosis--cannot be completely excluded. However, stable integration of the am gene can be obtained under a variety of other conditions, viz., using the am gene cloned in a phage lambda vector (J. A. Kinsey and J. A. Rambosek, Mol. Cell. Biol. 4:117-122, 1984), using derivatives of pJR2, or using pJR2 to transform a frameshift mutant.
Mol Cell Biol 1984 Oct
PMID:Transformation of Neurospora crassa with recombinant plasmids containing the cloned glutamate dehydrogenase (am) gene: evidence for autonomous replication of the transforming plasmid. 609 37

The formation of GABA from L-glutamate was investigated in homogenates of rat brain, liver, and kidney, using highly purified [14C]-L-glutamic acid as substrate and a thin-layer chromatographic separation of products. In agreement with other workers, liberation of [14C]-CO2 was found to be stoichiometric with GABA formation in brain homogenates, but not in liver or kidney extracts. Subcellular fractionation and dialysis experiments suggested that most of the GABA synthesis in these peripheral tissues, unlike brain, does not occur via a direct decarboxylation of glutamate and requires one or more cofactors other than pyridoxal phosphate. NAD stimulated GABA formation in dialyzed extracts, and inhibition of GABA-transaminase, both in vitro and in vivo, caused marked inhibition of GABA formation from glutamate in peripheral extracts. Although a very low GAD activity in liver and kidney cannot be excluded, these experiments suggest a major pathway from glutamate to GABA in these homogenates which includes (1) conversion of glutamate to alpha-ketoglutarate by glutamate dehydrogenase or transaminases, (2) conversion of alpha-ketoglutarate to succinic semialdehyde, and (3) formation of GABA from succinic semialdehyde and glutamate by GABA-transaminase.
Mol Cell Biochem 1981 Sep 25
PMID:Glutamate as a precursor of GABA in rat brain and peripheral tissues. 611 23

The effects of transcription and translation inhibitors on NADP-glutamate dehydrogenase and glutamine synthetase synthesis in nitrogen-starving Ankistrodesmus braunii cells have been studied. Considering the results obtained one can suggest that both enzymes are coded in a chloroplast genome and that during nitrogen starvation specific mRNA's are partly transferred from chloroplast into cytoplasm and can be translated there on 80S ribosomes.
Mol Cell Biochem 1982 Sep 03
PMID:The role of chloroplast and cytoplasm in the NADP-glutamate dehydrogenase and glutamine synthetase synthesis in Ankistrodesmus cells. 612 70

An amber mutation (glnA3711), the first nonsense mutation isolated in Klebsiella aerogenes, is described. When amber suppressors were present, the mutant made active glutamine synthetase which was more thermolabile than wild type, showing that glnA3711 lies in the structural gene for glutamine synthetase. Strains carrying the glnA3711 allele were unable to express nitrogen regulation of genes coding for histidase, asparaginase, and glutamate dehydrogenase unless amber suppressors were also present. These results support a model that expression of gene(s) from the glnA promoter is required for nitrogen regulation in K. aerogenes.
Mol Gen Genet 1982
PMID:A nonsense mutation in the structural gene for glutamine synthetase leading to loss of nitrogen regulation in Klebsiella aerogenes. 612 65

The effects of transcription and translation inhibitors on NADP-glutamate dehydrogenase and glutamine synthetase synthesis in nitrogen-starving Ankistrodesmus braunii cells have been studied. Considering the results obtained one can suggest that both enzymes are coded in the chloroplast genome and that during nitrogen starvation specific mRNA's are partly transferred from the chloroplast into the cytoplasm and can be translated there on 80S ribosomes.
Mol Cell Biochem 1982 Dec 10
PMID:The role of chloroplast and cytoplasm in the NADP-glutamate dehydrogenase and glutamine synthetase synthesis in Ankistrodesmus cells. 613 76

Mutants of the yeast Saccharomyces cerevisiae have been isolated which fail to derepress glutamine synthetase upon glutamine limitation. The mutations define a single nuclear gene, GLN3, which is located on chromosome 5 near HOM3 and HIS1 and is unlinked to the structural gene for glutamine synthetase, GLN1. The three gln3 mutations are recessive, and one is amber suppressible, indicating that the GLN3 product is a positive regulator of glutamine synthetase expression. Four polypeptides, in addition to the glutamine synthetase subunit are synthesized at elevated rates when GLN3+ cultures are shifted from glutamine to glutamate media as determined by pulse-labeling and one- and two-dimensional gel electrophoresis. The response of all four proteins is blocked by gln3 mutations. In addition, the elevated NAD-dependent glutamate dehydrogenase activity normally found in glutamate-grown cells is not found in gln3 mutants. Glutamine limitation of gln1 structural mutants has the opposite effect, causing elevated levels of NAD-dependent glutamate dehydrogenase even in the presence of ammonia. We suggest that there is a regulatory circuit that responds to glutamine availability through the GLN3 product.
Mol Cell Biol 1984 Dec
PMID:Regulation of glutamine-repressible gene products by the GLN3 function in Saccharomyces cerevisiae. 615 12

Glutamate synthase catalyzes glutamate formation from 2-oxoglutarate plus glutamine and plays an essential role when glutamate biosynthesis by glutamate dehydrogenase is not possible. Glutamate synthase activity has been determined in a number of Neurospora crassa mutant strains with various defects in nitrogen metabolism. Of particular interest were two mutants phenotypically mute except in an am (biosynthetic nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase deficient, glutamate requiring) background. These mutants, i and en-am, are so-called enhancers of am; they have been redesignated herein as en(am)-1 and en(am)-2, respectively. Although glutamate synthase levels in en(am)-1 were essentially wild type, the en(am)-2 strain was devoid of glutamate synthase activity under all conditions examined, suggesting that en(am)-2 may be the structural locus for glutamate synthase. Regulation of glutamate synthase occurred to some extent, presumably in response to glutamate requirements. Glutamate starvation, as in am mutants, led to enhanced activity. In contrast, glutamine limitation, as in gln-1 mutants, depressed glutamate synthase levels.
Mol Cell Biol 1981 Feb
PMID:Glutamate synthase levels in Neurospora crassa mutants altered with respect to nitrogen metabolism. 615 51

We used DNA containing the am gene of Neurospora crassa, cloned in the lambda replacement vector lambdaL-47 (this clone is designated lambdaC-10), and plasmid vector subclones of this DNA to transform am deletion and point mutant strains. By means of subcloning, all sequences required for transformation to am prototrophy and expression of glutamate dehydrogenase have been shown to reside on a 2.5-kilobase BamHI fragment. We also characterized several am+ strains that were obtained after transformation with lambdaC-10. These strains showed Mendelian segregation of the am+ gene, although less than 50% of the transformed strains showed the normal linkage relationship of am with inl. In all cases tested, the strains had incorporated lambda DNA as well. The lambda DNA also showed a Mendelian segregation pattern. In one case, the incorporation of am DNA in a novel position was associated with a mutagenic event producing a strain with a very tight colonial morphology. In all cases in which the am+ gene had become the resident of a new chromosome, glutamate dehydrogenase was produced to only 10 to 20% of the wild-type levels.
Mol Cell Biol 1984 Jan
PMID:Transformation of Neurospora crassa with the cloned am (glutamate dehydrogenase) gene. 623 May 18

Nutrients which stimulate insulin secretion are currently thought to initiate the series of cellular events eventually leading to insulin release either by interacting with a stereospecific receptor system (the regulatory site hypothesis) or by acting as a fuel (the substrate site hypothesis) in the pancreatic B-cell. The latter hypothesis is supported by a number of observations indicating that the capacity of nutrients to stimulate insulin release is indeed highly dependent on their capacity to increase catabolic fluxes in isolated pancreatic islets. However, these observations do not rule out the existence of nutrient receptors in islet cells. For instance, a nonmetabolized analog of L-leucine stimulates insulin release by causing allosteric activation of glutamate dehydrogenase, which should be considered, therefore, as a receptor for certain amino acids. Likewise, the increase in glycolytic flux, which is associated with the process of glucose-stimulated insulin release, is attributable not solely to a mass action phenomenon but also to the activation of phosphofructokinase by fructose 2.6-bisphosphate. The biosynthesis of this activator may involve a glucose receptor system. The fact that certain nutrient secretagogues (e.g. D-glucose and L-leucine) act in the B-cell both as substrates and enzyme activators permits reconciliation of the substrate site and regulatory site hypotheses for insulin release.
Mol Cell Biochem 1981 Jul
PMID:Insulin release: reconciliation of the receptor and metabolic hypotheses. Nutrient receptors in islet cells. 626 62

The influence of the relA1 mutation on the regulation of the ammonia assimilatory enzymes, glutamate dehydrogenase (EC 1.4.1.4), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.3), was examined. When cells grown in rich media (either Luria broth or glucose-ammonia plus casamino acids) were transferred to a glucose-ammonia medium, the relA mutant failed to resume growth and did not have the same increase in any of the assimilatory enzyme activities as the rel+ strain. This effect was particularly dramatic for glutamate dehydrogenase, which increased 6-fold in the rel+ strain. Measurements of the guanosine nucleotide concentrations showed that the rel+ strain had a ppGpp concentration about 9 times that of the relA mutant 5 min after the shift to minimal medium. These results are consistent with those for other biosynthetic enzymes and show that the ammonia assimilatory enzymes require a relA product for their synthesis during shift from rich to minimal media. In addition, we examined the response of these strains to a change in nitrogen source. The relA mutant again failed to resume growth after a shift from glucose-ammonia to glucose-arginine medium. Even though the ppGpp concentration did not increase, the rel+ strain grew and increased glutamine synthetase activities about 2-fold. These changes the absence of increased ppGpp levels suggest that some other relA-mediated function is important during this change in nitrogen source.
Mol Gen Genet 1982
PMID:The regulation of the ammonia assimilatory enzymes in Rel+ and Rel- strains of Salmonella typhimurium. 628 74


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