Relative activities of glutamine synthetase and glutaminase in mammalian synaptosomes

Ward, H. K.; Bradford, H. F.

doi:10.1111/j.1471-4159.1979.tb11737.x

Cited by 65 publications

(24 citation statements)

References 17 publications

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“…The increase in the activity of AAT and GPT during the postconvulsive stage was reduced Glutamine synthase activity in fasted rats was found to be 7.06 x lo3 & 0.35 (6) nmoles/min/mg protein, which is of the same order as values obtained by Ward and Bradford (1979). after the onset of seizure, (I) The onset of Picrotoxin induced seizure preconvulsive stage (98% and 124% for AAT and GPT respectively).…”

Section: G L U T a M I N E G A B Asupporting

confidence: 70%

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Changes in the Activity of Glutamate Related Enzymes in Cerebral Cortex, During Insulin-Induced Seizures

Abdul-Ghani

Ghneim

El-lati

et al. 1989

International Journal of Neuroscience

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The activity of glutamate related enzymes and the concentration of glutamine, glutamate and gamma-amino n-butyric acid (GABA) were investigated in the cerebral cortex of rats, in different stages of insulin-induced hypoglycemia. Hypoglycemia was produced by intraperitoneal injection of insulin 0.05-100 units per kg body weight. The minimum required dose to produce irreversible severe hypoglycemia was 0.5 units/kg. In 85% of the cases an insulin induced hypoglycemic convulsion, was achieved 130-150 minutes after injection. Blood glucose levels during insulin induced seizures ranged between 8-15 mg%. In the range of 0.5-100 u insulin/kg the degree of hypoglycemia and the onset of convulsions were identical. The concentration of glutamine was significantly reduced during convulsive and postconvulsive stages. Glutamate and GABA concentrations were reduced significantly in all stages of insulin-induced hypoglycemia. The decrease in glutamine concentration was concurrent with an increase in the activity of its degradative enzyme, glutaminase. This was apparent at the preconvulsive, convulsive and postconvulsive stages. The activity of other enzymes related to energy production such as glutamate dehydrogenase (GDH), glutamate transaminase (GPT) and aspartate aminotransferase (AAT) were also increased. The activity of glutamine synthase (GS) was unaffected by hypoglycemia. Insulin induced changes in glutamine, glutamate and their related enzymes could not be attributed to convulsion since a similar pattern of changes was observed in the preconvulsive and postconvulsive stages, and no changes were detected following picrotoxin-induced seizures.

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Section: G L U T a M I N E G A B Asupporting

confidence: 70%

“…Glutamine synthase activity in brain cortical tissue was assayed using the method described by Ward and Bradford (1979).…”

Section: Determination Oj'enzyme Aciivitiesmentioning

confidence: 99%

Changes in the Activity of Glutamate Related Enzymes in Cerebral Cortex, During Insulin-Induced Seizures

Abdul-Ghani

Ghneim

El-lati

et al. 1989

International Journal of Neuroscience

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“…The increased concentration of glutamine in the hyperammonemic rabbit brain presented in this study is expected, since ammonia is thought to both increase synthesis and inhibit the activity of glutaminase (e.g. Ward and Bradford, 1979). Indeed, the concentration of cerebral [5-"N]glutamine is significantly higher, about fivefold (5.2 pmol/ 100 mg protein), than that of "N glutamate (1.1 pmo1/100 mg protein) (Table 3).…”

Section: Resultsmentioning

confidence: 59%

Quantitation of Metabolic Compartmentation in Hyperammonemic Brain by Natural Abundance ¹³C‐NMR Detection of ¹³C‐¹⁵N Coupling Patterns and Isotopic Shifts

Lapidot¹

1997

European Journal of Biochemistry

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In the present study, the removal of cerebral ammonia by glutamine synthetase (GS) and by reductive amination of 2-oxoglutarate by glutamate dehydrogenase in the presence of an amino donor group, was determined in hyperammonemic rabbit brains.The "N enrichments of brain metabolite a-amino and amide positions of glutamine, glutamate, and alanine were determined by the indirect detection of ' Wlabeled compounds of the lT-''N spin coupling patterns of natural abundance IT-NMR spectra. The 'IC-NMR spectra of brain extracts were obtained from rabbits infused with "NH,CI with or without intraperitoneal infusion of the GS inhibitor, L-methionine DL-sulfoximine, in a reasonable acquisition time period. When "NH,CI was infused, ]alanine concentrations (2.9 pmoM00 mg protein and 1.8 pmol/l00 mg protein, respectively). These findings and those obtained from 'T-''C isotopomer analysis (Lapidot and Gopher, 1994b) suggest that astrocytic 2-oxoglutarate is partially utilized (together with an amino group donor) as a precursor for neuronal glutamate in the hyperammonemic brain when GS is inhibited. This process can partly replace GS activity in metabolizing ammonia in the hyperammonemic rabbit brain.

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“…Glutamine synthetase activity was measured according to Ward and Bradford (20). Aliquots of 120 μl cell homogenate were incubated with 100 μl of reaction mixture at 37°C.…”

Section: Methodsmentioning

confidence: 99%

Ammonia induces MK‐801‐sensitive nitration and phosphorylation of protein tyrosine residues in rat astrocytes

et al. 2002

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Astrocytes play a key role in the pathogenesis of ammonia-induced neurotoxicity and hepatic encephalopathy. As shown here, ammonia induces protein tyrosine nitration in cultured rat astrocytes, which is sensitive to the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. A similar pattern of nitrated proteins is produced by NMDA. Ammonia-induced tyrosine nitration depends on a rise in [Ca2+]i, IkB degradation, and NO synthase (iNOS) induction, which are prevented by MK-801 and the intracellular Ca2+ chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Moreover, the increase in tyrosine nitration is blunted by L-NMMA, 1400W, uric acid, Cu, Zn-superoxide dismutase/catalase treatment, and methionine-sulfoximine, which indicate the involvement of reactive nitrogen intermediates and intracellular glutamine accumulation. Such reactive nitrogen intermediates additionally mediate ammonia-induced phosphorylation of the MAP-kinases Erk-1/Erk-2 and p38MAPK. Among the proteins, which are tyrosine -nitrated by ammonia, glyceraldehyde-3-phosphate dehydrogenase, the peripheral-type benzodiazepine receptor, Erk-1, and glutamine synthetase are identified. Ammonia-induced nitration of glutamine synthetase is associated with a loss of enzymatic activity. Astroglial protein tyrosine nitration is found in brains from rats after acute ammonia-intoxication or after portacaval anastomosis, indicating the in vivo relevance of the present findings. The production of reactive nitrogen intermediates and protein tyrosine nitration may alter astrocyte function and contribute to ammonia neurotoxicity.

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Relative activities of glutamine synthetase and glutaminase in mammalian synaptosomes

Cited by 65 publications

References 17 publications

Changes in the Activity of Glutamate Related Enzymes in Cerebral Cortex, During Insulin-Induced Seizures

Changes in the Activity of Glutamate Related Enzymes in Cerebral Cortex, During Insulin-Induced Seizures

Quantitation of Metabolic Compartmentation in Hyperammonemic Brain by Natural Abundance ¹³C‐NMR Detection of ¹³C‐¹⁵N Coupling Patterns and Isotopic Shifts

Ammonia induces MK‐801‐sensitive nitration and phosphorylation of protein tyrosine residues in rat astrocytes

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Relative activities of glutamine synthetase and glutaminase in mammalian synaptosomes

Cited by 65 publications

References 17 publications

Changes in the Activity of Glutamate Related Enzymes in Cerebral Cortex, During Insulin-Induced Seizures

Changes in the Activity of Glutamate Related Enzymes in Cerebral Cortex, During Insulin-Induced Seizures

Quantitation of Metabolic Compartmentation in Hyperammonemic Brain by Natural Abundance 13C‐NMR Detection of 13C‐15N Coupling Patterns and Isotopic Shifts

Ammonia induces MK‐801‐sensitive nitration and phosphorylation of protein tyrosine residues in rat astrocytes

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Quantitation of Metabolic Compartmentation in Hyperammonemic Brain by Natural Abundance ¹³C‐NMR Detection of ¹³C‐¹⁵N Coupling Patterns and Isotopic Shifts