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At least 271 records · Page 15Linked to original sources
PubMed1967

Genetic analysis of glutamate transport and glutamate decarboxylase in Escherichia coli.

The location of the Escherichia coli K-12 genes determining or regulating glutamate transport, and the location of the gene determining glutamate decarboxylase synthesis, were established by conjugation. The ability to grow on glutamate as the sole source of carbon and energy was used to select for glutamate transport recombinants. Two genes determining the ability to grow on glutamate as the sole source of carbon and energy were mapped. One (gltC) is located near mtl (mannitol), and the other (gltH) appears to be located between the gal (galactose) and trp (tryptophan) loci. The glutamate decarboxylase gene (gad) is strongly linked to gltC. The gltC(+) recombinants grow on glutamate much faster and accumulate this amino acid to a greater extent than do the gltH(+) recombinants. The gltH(+) gene functioned only in one female strain (P678), whereas the gltC gene functioned in all the female strains tested (P678, C600, W1).

Biological Transport↗
PubMed2006

Ciliary neurotrophic factor activates astrocytes, redistributes their glutamate transporters GLAST and GLT-1 to raft microdomains, and improves glutamate handling in vivo.

To study the functional role of activated astrocytes in glutamate homeostasis in vivo, we used a model of sustained astrocytic activation in the rat striatum through lentiviral-mediated gene delivery of ciliary neurotrophic factor (CNTF). CNTF-activated astrocytes were hypertrophic, expressed immature intermediate filament proteins and highly glycosylated forms of their glutamate transporters GLAST and GLT-1. CNTF overexpression produced a redistribution of GLAST and GLT-1 into raft functional membrane microdomains, which are important for glutamate uptake. In contrast, CNTF had no detectable effect on the expression of a number of neuronal proteins and on the spontaneous glutamatergic transmission recorded from striatal medium spiny neurons. These results were replicated in vitro by application of recombinant CNTF on a mixed neuron/astrocyte striatal culture. Using microdialysis in the rat striatum, we found that the accumulation of extracellular glutamate induced by quinolinate (QA) was reduced threefold with CNTF. In line with this result, CNTF significantly increased QA-induced [(18)F]-fluoro-2-deoxyglucose uptake, an indirect index of glutamate uptake by astrocytes. Together, these data demonstrate that CNTF activation of astrocytes in vivo is associated with marked phenotypic and molecular changes leading to a better handling of increased levels of extracellular glutamate. Activated astrocytes may therefore be important prosurvival agents in pathological conditions involving defects in glutamate homeostasis.

Animals↗
PubMed2005

Glutamate transporter studies reveal the pruning of metabotropic glutamate receptors and absence of AMPA receptor desensitization at mature calyx of Held synapses.

We examined the effect of glutamate transporter blockade at the calyx of Held synapse. In immature synapses [defined as postnatal day 8 (P8) to P10 rats], transporter blockade causes tonic activation of NMDA receptors and strong inhibition of the AMPA receptor-mediated EPSC amplitude. EPSC inhibition was blocked with a metabotropic glutamate receptor (mGluR) antagonist [1 microm LY341495 (2S-2-amino-2-(1S,2S-2-carboxycycloprop-1-yl)-3-(xanth-9-yl)propanoic acid)], suggesting that elevated resting glutamate concentration specifically activates group II and group III mGluRs. Using mGluR subtype-specific agonists and antagonists, we determined that increased glutamate activates presynaptic mGluR2/3 and mGluR8 receptors but not mGluR4, although this receptor is present. Surprisingly, in older animals (P16-P18), transporter blockade had no effect on EPSC amplitude because of a developmental downregulation of group II/III mGluR activation in rats and mice. In contrast to other CNS synapses, we observed no effect of transporter blockade on EPSC decay kinetics, although expression of glutamate transporters was strong in nearby glial processes at both P9 and P17. Finally, using a low-affinity AMPA receptor antagonist (gamma-D-glutamylglycine), we show that desensitization occurs at P8-P10 but is absent at P16-P18, even during trains of high-frequency (100-300 Hz) stimulation. We suggest that diffusion and transporter activation are insufficient to clear synaptically released glutamate at immature calyces, resulting in significant desensitization. Thus, mGluRs may be expressed in the immature calyx to help limit glutamate release. In the more mature calyx, there is a far smaller diffusional barrier attributable to the highly fenestrated synaptic terminal morphology, so AMPA receptor desensitization is avoided and mGluR-mediated inhibition is not necessary.

Animals↗
PubMed1985

[Studies on the mechanism of placental transport of L-glutamate (the effect of K+ in microvillous vesicles on L-glutamate uptake)].

The effect of potassium ion and membrane potential on the uptake of L-glutamate in microvilli (brush border) vesicles prepared from human term placenta was studied using a rapid filtration technique. The uptake of L-glutamate into microvilli vesicles is Na+ electrochemical gradient dependent and pre-equilibration of the vesicles with K+ stimulates L-glutamic acid uptake. Imposition of a K+ gradient (K+ in greater than K+ out) enhances Na+-dependent L-glutamate uptake. Changes in membrane potential due to the imposition of anion replacement markedly affect Na+ dependent L-glutamate uptake only in the presence of K+. However, this effect is not significant when changes in membrane potential incur following the imposition of valinomycin induced by K+ diffusion potential. The data indicate that Na+-dependent L-glutamate transport can be additionally energized by a K+ gradient. Furthermore K+ renders Na+-dependent L-glutamate transport sensitive to changes in the transmembrane potential difference.

Cell Membrane Permeability↗
PubMed1994

Determination of L-glutamate using flow injection analysis with immobilized L-glutamate oxidase reactor.

L-Glutamate oxidase (GOD) and horseradish peroxidase (HRP) were covalently coupled on alkylamine pretreated controlled pore glass (CPG) by means of glutaraldehyde. The immobilized enzymes were packed into a teflon tube and used in flow injection analysis (FIA) system for L-glutamate determination. A good linearity range was obtained at 0.1-2.0 mM, and the coefficient of variation was 0.7% (n = 8). More than 80 samples were measured within an hour. The stability of the immobilized GOD reactor was good, retaining 50% of its initial activity after 4 months storage in buffer at 4 degrees C. When the concentration of L-glutamate remained lower than 2.5 mM, the determination of L-glutamate in this system was not affected by pH and temperature within the range of 6.0-8.0 and 20-35 degrees C, respectively. The system was applied to determine L-glutamate in broth samples during L-glutamate fermentation and good correlations were achieved between results obtained with the FIA system, L-glutamate oxidase kit and Warburg's method.

Amino Acid Oxidoreductases↗
PubMed1993

Glutamate and imprinting memory: the role of glutamate receptors in the encoding of imprinting memory.

Glutamate-sensitive receptors have been implicated in many forms of neural plasticity and learning, including imprinting of chicks. Previous studies have indicated that glutamate binding levels in the left intermediate medial hyperstriatum ventrale (IMHV) region of the chick forebrain increase as a correlate of the acquisition of an imprinting memory; however, it has not been determined whether this is due to an increase in the number of glutamate receptors or to increased receptor affinity. The area specificity of these changes, within the left and right hemisphere, was also unexplored. We have performed Scatchard displacement binding analyses to examine changes in both the number and affinity of glutamate receptors in the left and right hyperstriatum ventrale (HV) and also the left and right archistriatal/lobus parolfactorius (AS/LPO) areas from imprinted and non-imprinted chicks. The results of this study demonstrate lateralised increases in both the number and affinity of glutamate receptors in the left HV area at 7-8 h after imprinting. Significant increases in the affinity, but not the number, of glutamate receptors were found in the left AS/LPO. This suggests that the left AS/LPO, which has previously been shown to be involved in the acquisition of a passive avoidance memory, may also be involved in the formation of an imprinting memory.

Animals↗
PubMed1986

Effect of sucrose ingestion on plasma glutamate concentrations in humans administered monosodium L-glutamate.

Plasma glutamate concentrations in human subjects are markedly lower when monosodium L-glutamate (MSG) is ingested in consomme with starch than when ingested in consomme alone. This study investigated whether sucrose had a similar effect. Six normal adult subjects (three male, three female) ingested two servings of beef consomme each providing 50 mg MSG/kg body weight in a randomized crossover design. One serving of consomme contained no added carbohydrate; the other provided 0.5 g sucrose/kg body weight. Ingestion of the consomme without sucrose significantly (p less than 0.05) increased the mean plasma glutamate concentration from baseline (4.44 +/- 0.97 mumol/dl) to a peak value of 18.1 +/- 6.99 mumol/dl 30 min after dosing. The area under the plasma glutamate concentration-time curve was 553 +/- 238 mumol/dl X min. When the consomme contained 0.5 g sucrose/kg body weight, both the mean peak plasma glutamate concentration (5.48 +/- 2.19 mumol/dl) and the area under the curve (105 +/- 46 mumol/dl X min) were significantly lower. These data confirm that metabolizable carbohydrate has a significant effect on plasma glutamate concentration response after MSG loading.

Administration, Oral↗
PubMed1987

[Molecular organization of glutamate-sensitive chemo-stimulated nerve cell membranes. Interaction of monoclonal antibodies with glutamate-binding membrane proteins in the rat brain, human neuroblastoma and molluscan neurons].

Hybrid cells obtained by fusion of myeloma PX63-Ag8-653 with immune splenocytes of BALB/c mice were found to produce monoclonal antibodies with a high degree of specificity to rat and human brain. The kinetics of specific IgG binding to purified fractions of glutamate-binding membrane proteins from rat and human brain were analyzed in Scatchard plots. The presence of a single type of binding sites with Kd = 100 nM was demonstrated. The monoclonal antibodies were shown to inhibit the specific binding of tritium-labeled L-glutamate to different brain synaptic membranes. Addition of monoclonal antibodies to the incubation medium induced a modulating effect of physiological responses to L-glutamate in Planorbarius corneus neurons. The possible use of specific antibodies to glutamate-binding proteins as immunochemical markers for the study of glutamate receptor topography on membrane surface was demonstrated with the aid of neuroblastoma cells N18 Tg2a and rat brain tissue slices. An analysis of glutamate receptor binding sites with the use of monoclonal antibodies revealed that these antibodies specifically recognize the active center in the receptor molecules which have identical antigen determinant sites in different biological systems.

Animals↗
PubMed1982

[Glutamate dehydrogenase from rat brain. Properties of the enzyme when acting in the direction of glutamate degradation].

Several aspects on regulation of rat brain glutamate dehydrogenase when the enzyme catalyses the reaction of glutamate degradation have been studied. The 2-oxo-glutarate is a competitive inhibitor against glutamate and NADH competes with NAD. The enzyme seems to have three sites of binding for glutamate, two of them bind the alpha and gamma carboxylic groups and the other the NH2-group of glutamate. Between the binding of two -COO- groups, the site on the enzyme which binds the gamma -COO- group of glutamate seems to be more important than the alpha one.

Allosteric Regulation↗
PubMed1988

Characterization of the RNA Required for Biosynthesis of delta-Aminolevulinic Acid from Glutamate : Purification by Anticodon-Based Affinity Chromatography and Determination That the UUC Glutamate Anticodon Is a General Requirement for Function in ALA Biosynthesis.

The heme and chlorophyll precursor delta-aminolevulinic acid acid (ALA) is formed in plants and algae from glutamate in a process that requires at least three enzyme components plus a low molecular weight RNA which co-purifies with the tRNA fraction during DEAE-cellulose column chromatography. RNA that is effective in the in vitro ALA biosynthetic system was extracted from several plant and algal species that form ALA via this route. In all cases, the effective RNA contained the UUC glutamate anticodon, as determined by its specific retention on an affinity resin containing an affine ligand directed against this anticodon. Construction of the affinity resin was based on the fact that the UUC glutamate anticodon is complementary to the GAA phenylalanine anticodon. By covalently linking the 3' terminus of yeast tRNA(Phe(GAA)) to hydrazine-activated polyacrylamide gel beads, a resin carrying an affine ligand specific for the anticodon of tRNA(Glu(UUC)) was obtained. Column chromatography of plant and algal RNA extracts over this resin yielded a fraction that was highly enriched in the ability to stimulate ALA formation from glutamate when added to enzyme extracts of the unicellular green alga Chlorella vulgaris. Enhancement of ALA formation per A(260) unit added was as much as 50 times greater with the affinity-purified RNA than with the RNA before affinity purification. The affinity column selectively retained RNA which supported ALA formation upon chromatography of RNA extracts from species of the diverse algal groups Chlorophyta (Chlorella Vulgaris), Euglenophyta (Euglena gracilis), Rhodophyta (Cyanidium caldarium), and Cyanophyta (Synechocystis sp. PCC 6803), and a higher plant (spinach). Other glutamate-accepting tRNAs that were not retained by the affinity column were ineffective in supporting ALA formation. These results indicate that possession of the UUC glutamate anticodon is a general requirement for RNA to participate in the conversion of glutamate to ALA in plants and algae.

Journal Article↗
PubMed1983

Regulation of folylpoly-gamma-glutamate synthesis in bacteria: in vivo and in vitro synthesis of pteroylpoly-gamma-glutamates by Lactobacillus casei and Streptococcus faecalis.

Lactobacillus casei and Streptococcus faecalis accumulated labeled folic acid and metabolized this compound to poly-gamma-glutamates of chain lengths of up to 11 and 5, respectively. Octa- and nonaglutamates predominated in L. casei, and tetraglutamates predominated in S. faecalis. The most effective monoglutamate substrates for the L. casei and S. faecalis folylpoly-gamma-glutamate (folylpolyglutamate) synthetases were methylene- and formyltetrahydrofolate, respectively. Methylenetetrahydropteroylpoly-gamma-glutamates were the preferred poly-gamma-glutamate substrates for both enzymes and, in each case, the highest activity was observed with the diglutamate substrate. The final distribution of folylpolyglutamates in these bacteria appeared to reflect the ability of folates with various glutamate chain lengths to act as substrates for the bacterial folylpolyglutamate synthetases. The proportions of individual folylpolyglutamates were markedly affected by culturing the bacteria in medium containing adenine, whereas thymine was without effect. Adenine did not affect the level of folylpolyglutamate synthetase in either organism but caused a large increase in the proportion of intracellular folates containing one-carbon units at the oxidation level of formate, folates which are substrates for enzymes involved in purine biosynthesis. The folates with shorter glutamate chain lengths in bacteria cultured in the presence of adenine resulted from primary regulation of the de novo purine biosynthetic pathway, regulation which caused an accumulation of formyltetrahydropteroyl-poly-gamma-glutamates (folate derivatives that are ineffective substrates for folylpolyglutamate synthetases), and did not result from regulation of folylpolyglutamate synthetase per se.

Adenine↗
PubMed1988

Fine distribution of gamma-aminobutyric acid, glutamic acid decarboxylase, and glutamic acid in the rabbit cerebellum.

The fine distribution of GABA, glutamic acid decarboxylase, and glutamic acid within each layer of the rabbit cerebellar cortex was determined with microanalytical methods. The greatest glutamic acid decarboxylase activity and the highest GABA concentration were found in the Purkinje cell layer. In the distribution of GABA and glutamic acid decarboxylase the peak of glutamic acid decarboxylase activity was more pronounced than that of GABA; the concentration of glutamic acid did not show much variation between each layer.

Animals↗
PubMed1987

Use of cystine to distinguish glutamate binding from glutamate sequestration.

Cystine is shown to be a high-affinity substrate for the chloride-dependent glutamate exchange system in brain membranes, which mediates what has previously been considered chloride-dependent glutamate 'binding'. Similarities in the pharmacological profile and in kinetic properties suggest that this transport system may be a high-affinity adaptation of the transport system xc- present in somatic cells. Since cystine selectively inhibits glutamate sequestration and does not interact with the major glutamate binding sites, it can be used to assess the contribution of sequestration to overall 'binding' of glutamate or glutamate-analogs or to suppress sequestration in receptor binding assays. As an example, it is shown that more than 90% of 'bound' [3H]aminophosphonobutyrate [( 3H]APB) is displaced by cystine and should be interpreted as APB sequestration.

Animals↗
PubMed1995

Extracellular glutamate levels in the hypothalamus and hippocampus of rats after acute or chronic oral intake of monosodium glutamate.

Using brain microdialysis we studied the effect of high doses of monosodium glutamate (MSG) on the extracellular concentration of glutamate in the hypothalamus and in the hippocampus of freely moving rats. MSG at 4 g/kg (40% solution) given by gavage caused a significant increase in plasma (5.3 +/- 0.4-fold, P < 0.01) and extracellular glutamate in the hippocampus (4.2 +/- 0.6-fold, P < 0.01) and in the hypothalamus (8.9 +/- 1.7-fold, P < 0.01) compared to control rats receiving a 40% sucrose solution (10 ml/kg). The peak increase was found within 40 min after MSG administration then declining to baseline in the next 80 min. No changes were found in glutamate tissue concentrations. Twenty-one days after ad libitum MSG intake with the diet (approximately 4 g/kg) no changes were found, in plasma, in extracellular and tissue concentration of glutamate in the hypothalamus compared to rats fed with a normal diet. Glutamate release induced by 200 mM KCl was not modified as well. Histological analysis of Nissl-stained brain tissue slices did not reveal any obvious cell loss in the hippocampus after acute or chronic MSG administration.

Administration, Oral↗
PubMed1998

Taste dimensions of monosodium glutamate (MSG) in a food system: role of glutamate in young American subjects.

Freshly cooked chicken broth was prepared with several concentrations (0.06-0.32 M) of added NaCl. In the first study, subjects were presented with pairs of samples, each having the same concentration of NaCl (salt) but one of which contained 0.01 M monosodium glutamate (MSG). The subjects preferred the sample with added MSG when the salt levels were low to moderate. The next two studies were designed to determine the relative role of the added sodium and glutamate in MSG in enhancing palatability. In the second study, NaCl was added in amounts equivalent to the sodium in 0.01 M MSG to one of the two samples. Subjects preferred the one with more salt at the low salt level indicating that the added sodium played a role in enhancing palatability. In the last study, the concentration of sodium was held constant in the soups but the glutamate was varied by adding 0.01 M MSG to one sample and 0.01 M NaCl to the other. Subjects preferred the sample with added glutamate to the one without, at the moderate salt concentrations, demonstrating a role for glutamate alone in enhancing palatability. These studies, in sum, demonstrate that MSG increases palatability of salted soups and that both the sodium and the glutamate independently contribute to this enhancement.

Adult↗
PubMed2001

Neuronal glutamate transporters control activation of postsynaptic metabotropic glutamate receptors and influence cerebellar long-term depression.

Neuronal and glial isoforms of glutamate transporters show distinct distributions on membranes surrounding excitatory synapses, but specific roles for transporter subtypes remain unidentified. At parallel fiber (PF) synapses in cerebellum, neuronal glutamate transporters and metabotropic glutamate receptors (mGluRs) have overlapping postsynaptic distributions suggesting that postsynaptic transporters selectively regulate mGluR activation. We examined interactions between transporters and mGluRs by evoking mGluR-mediated excitatory postsynaptic currents (mGluR EPSCs) in slices of rat cerebellum. Selective inhibition of postsynaptic transporters enhanced mGluR EPSCs greater than 3-fold. Moreover, impairing glutamate uptake facilitated mGluR-dependent long-term depression at PF synapses. Our results demonstrate that uniquely positioned glutamate transporters strongly influence mGluR activation at cerebellar PF synapses. Postsynaptic glutamate uptake may serve as a general mechanism for regulating mGluR-initiated synaptic depression.

ATP-Binding Cassette Transporters↗
PubMed1978

Inactivation of glutamate dehydrogenase and glutamate synthase from Bacillus megaterium by phenylglyoxal, butane-2,3-dione and pyridoxal 5'-phosphate.

Reaction of phenylglyoxal with glutamate dehydrogenase (EC 1.4.1.4), but not with glutamate synthase (EC 2.6.1.53), from Bacillus megaterium resulted in complete loss of enzyme activity. NADPH alone or together with 2-oxoglutarate provided substantial protection from inactivation by phenylglyoxal. Some 2mol of [14C]Phenylglyoxal was incorporated/mol of subunit of glutamate dehydrogenase. Addition of 1mM-NADPH decreased incorporation by 0.7mol. The Ki for phenylglyoxal was 6.7mM and Ks for competition with NADPH was 0.5mM. Complete inactivation of glutamate dehydrogenase by butane-2,3-dione was estimated by extrapolation to result from the loss of 3 of the 19 arginine residues/subunit. NADPH, but not NADH, provided almost complete protection against inactivation. Butane-2,3-dione had only a slight inactivating effect on glutamate synthase. The data suggest that an essential arginine residue may be involved in the binding of NADPH to glutamate dehydrogenase. The enzymes were inactivated by pyridoxal 5'-phosphate and this inactivation increased 3--4-fold in the borate buffer. NADPH completely prevented inactivation by pyridoxal 5'-phosphate.

Aldehydes↗
PubMed1988

Measurement of the transfer of the nitrogen moiety of intestinal lumen glutamic acid in man after oral ingestion of l-[15N]glutamic acid.

1. The measurement of the intestinal metabolism of the nitrogen moiety of glutamic acid has been investigated by oral ingestion of l-[15N]glutamic acid and sampling of arterialized blood. 2. Measurements have been made in six normal adults weighing an average of 72.8 kg ingesting 100 mg of l-[15N]glutamic acid after an overnight fast. 3. Measurement of the enrichment of arterial glutamic acid, glutamine and alanine was by gas chromatography-mass spectrometry. Isotopic enrichment of the amino acids was followed for 150 min after the ingestion of the amino acid. 4. Arterialized venous blood amino acid concentrations, measured by h.p.l.c., demonstrated no significant changes during the course of the experiment. 5. From the observed appearance of label in arterialized glutamic acid, alanine and glutamine, little luminal glutamic acid reaches the extracellular pool. The majority of the administered nitrogen label appears in the arterial alanine and glutamine components.

Administration, Oral↗