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PubMed1982

Characterization of glutamic acid decarboxylase activity in cerebral blood vessels.

Glutamic acid decarboxylase activity associated with cerebral blood vessels appears to be part of a specific cerebrovascular system involving gamma-aminobutyric acid. This activity was characterized kinetically and pharmacologically and compared with that in brain and several nonneuronal tissues. Formation of gamma-aminobutyric acid from [14C]glutamate was measured in a soluble extract of pia-arachnoid blood vessels isolated from bovine brain. The vascular activity was like brain glutamate decarboxylase in that it required pyridoxal phosphate, was completely inhibited by aminooxyacetic acid, and had a similar affinity for glutamate. Cerebrovascular decarboxylase activity differed, however, from brain decarboxylase in that it was less sensitive to sulfhydryl reagents, was stimulated by 3-mercaptopropionic and cysteic acids, and was competitively inhibited by cysteine sulfinic acid. The glutamate decarboxylase activity of the cerebral vessels was similar to that in renal cortex and mesenteric blood vessels in its responses to sulfhydryl reagents and 3-mercaptopropionic acid. These findings are consistent with previous suggestions of a nonneuronal form of the enzyme and offer the possibility that synthesis of gamma-aminobutyric acid in cerebral blood vessels can be manipulated independently from that in neuronal tissue.

Animals↗
PubMed1965

Metabolism of glutamic acid in a mutant of Escherichia coli.

Vender, Joyce (Indiana University, Bloomington), Kunthala Jayaraman, and H. V. Rickenberg. Metabolism of glutamic acid in a mutant of Escherichia coli. J. Bacteriol. 90:1304-1307. 1965.-A mutant strain of Escherichia coli W1485 was selected for its ability to utilize glutamic acid as the sole source of carbon. Growth of the mutant on glutamic acid led to the repression of glutamic acid dehydrogenase formation. The mutant differed from the wild-type strain in that glutamic decarboxylase activity was absent from the mutant under conditions of growth which supported the formation of this enzyme in the parent strain. Evidence is presented which suggests that loss of the decarboxylase activity results in the acquisition of the ability to utilize glutamic acid as sole source of carbon; a pathway of glutamate utilization via transamination is proposed.

Chromatography, Paper↗
PubMed2002

Synthesis and pharmacology of 3-hydroxy-delta2-isoxazoline-cyclopentane analogues of glutamic acid.

The synthesis and pharmacology of two potential glutamic acid receptor ligands are described. Preparation of the bicyclic 3-hydroxy-delta2-isoxazoline-cyclopentane derivatives (+/-)-7 and (+/-)-8 was accomplished via 1,3-dipolar cycloaddition of bromonitrile oxide to suitably protected 1-amino-cyclopent-3-enecarboxylic acids. Their structure was established using a combination of 1H NMR spectroscopy and molecular mechanics calculations carried out on the intermediate cycloadducts (+/-)-11 and (+/-)-12. Amino acid derivatives (+/-)-7 and (+/-)-8 were assayed at ionotropic and metabotropic glutamic acid receptor subtypes and their activity compared with that of trans-ACPD and cis-ACPD. The results show that the replacement of the omega-carboxylic group of the model compounds with the 3-hydroxy-delta2-isoxazoline moiety abolishes or reduces drastically the activity at the metabotropic glutamate receptors. Conversely, on passing from cis-ACPD to derivative (+/-)-8, the agonist activity at NMDA receptors is almost unaffected.

Amino Acids↗
PubMed1978

Mechanism of the stereospectific irreversible inhibition of bacterial glutamic acid decarboxylase by (R)-(--)-4-aminohex-5-ynoic acid, an analogue of 4-aminobutyric acid.

4-Aminohex-5-ynoic acid inhibits bacterial glutamic acid decarboxylase in a time-dependent irreversible manner. The inhibition is stereospecific and requires the abstraction of the propargylic hydrogen from 4(R)-(--)-4-aminohex-5-ynoic acid. This leads to the generation of a reactive alkylating agent in the active site which can react with a nucleophilic residue. At complete inhibition, there is incorporation of one molecule of inhibitor per pyridoxal binding site. If the decarboxylation of glutamate occurs with retention of configuration, the irreversible inhibition of this enzyme by the 4-(R) isomer can be rationalized on the basis of reversibility of the protonation step in the normal catalytic mechanism.

Aminocaproates↗
PubMed1978

Isolation and identification of beta-citryl-L-glutamic acid from newborn rat brain.

An unknown compound containing glutamic acid residue was found in newborn rat brain. The compound occurred predominantly in brain. Its concentration was approx. 1 mumol/g tissue at birth and decreased to one-tenth 24 days after birth. The compound was isolated from newborn rat brains, and subjected to elementary analysis and to infrared and mass spectrometric analysis. Glutamic acid and citric acid were formed from the compound on acid hydrolysis. The compound was presumed to be a citrylglutamic acid. Two isomers, alpha- and beta-citrylglutamic acid, were synthesized. The unknown compound was identified as beta-citryl-L-glutamic acid. The occurence of this compound has not been reported in nature.

Animals↗
PubMed1983

The release and neosynthesis of glutamic acid are increased in experimental models of hepatic encephalopathy.

The effects of ammonium ions on the release of glutamic acid from the rat cerebral cortex were measured in vivo using cortical cups and a multiple ion detection technique. The neosynthesis of this amino acid from glucose was also studied in two experimental models of hepatic encephalopathy: (1) rats receiving large amounts of ammonium acetate (i.p.) and (2) rats with a surgically constructed portocaval anastomosis. Intraperitoneal administration of 8 mmol/kg of ammonium acetate increased the cortical release of glutamic acid from 9.1 +/- 0.8 to 19 +/- 2 (nmol X cm-2 X min-1). Moreover, 20 min after ammonium acetate administration the rate of incorporation of 13C2, originating from [13C]glucose, into glutamic acid increased by 65%. In several brain areas of rats bearing a portocaval anastomosis and fed ad libitum for 4 weeks, the content of glutamic acid slightly increased and the rate of formation of [13C2]glutamate from [13C]glucose approximately doubled. These results indicate that ammonium ions increase the release and the formation of glutamic acid in the brain. The resulting increased concentration of this amino acid in the extracellular spaces may be one of the mechanisms of ammonia toxicity in vivo.

Acetates↗
PubMed1984

Glutamic acid and glutamine levels in serum and cerebrospinal fluid in hepatic encephalopathy.

Significant elevation of glutamic acid and glutamine concentrations in CSF was observed in hepatic encephalopathic patients with fulminant hepatitis and liver cirrhosis. However, the ratios of CSF glutamic acid to CSF glutamine levels and of CSF to serum glutamic acid and glutamine levels were significantly higher only in cirrhotic patients with hepatic encephalopathy. CSF glutamine levels were positively correlated with blood ammonia and CSF tyrosine levels in cirrhotic patients. The results indicate that CSF glutamic acid and glutamine levels are important tools in diagnosing hepatic encephalopathy in severe liver disease.

Adult↗
PubMed1981

[Influence of chloramphenicol on glutamic acid excretion in citrobacter intermedius C3 (author's transl)].

Chloramphenicol inhibits growth of C. intermedius C3 along with glutamic acid excretion, isocitrate dehydrogenase, glutamate dehydrogenase and the percentage of glutamic acid excreting colonies in solid medium. Repression of isocitrate dehydrogenase and glutamate dehydrogenase may explain the observed decrease in extracellular glutamic acid accumulation even when media were supplemented with 2-oxoglutarate, a known inducer of excretion in C. intermedius C3.

Cell Division↗
PubMedDate not supplied

Protective effect of glutamic acid on cardiac function and metabolism during cardioplegia and reperfusion.

The effect of glutamic acid added to cardioplegic solution containing 20 mM K+ on the cardiac function and metabolism was studied in isolated working rat hearts. 30-min cardiac arrest resulted in profound fall in creatine phosphate and ATP content, by four- and two-fold, respectively, as well as in four-fold rise in AMP content. Simultaneously, during cardioplegia a decline in tissue glutamate and aspartate content and an increase in tissue ammonia and alanine content were found. After reperfusion, an incomplete restoration of ATP, AMP, and creatine phosphate content were observed; the cardiac output recovered only to 39 percent of the initial value. An addition of glutamic acid to cardioplegic solution was associated with significantly less decline in the content of high-energy phosphates and less prominent rise in AMP content during cardioplegia. It also prevented the decline in tissue aspartate content and caused a lesser ammonia accumulation in myocardial tissue due to the activation of glutamine synthesis. In spite of this the tissue ammonia level remained elevated. Reperfusion with Krebs-Henseleit buffer resulted in the recovery of cardiac output to 75% of the initial value as well as better restoration of high-energy phosphate content. The addition of glutamic acid in the perfusate during reperfusion led to further improvement of ATP and creatine phosphate content. It is suggested that an addition of glutamic acid may have beneficial effect in open heart surgery.

Adenine Nucleotides↗
PubMed1991

Stimulation of 22Na+ efflux from rat forebrain membrane vesicles by L-glutamic acid, L-aspartic acid and kainic acid.

A glass fiber filter assay method is described for measuring 22Na+ efflux stimulated by L-glutamic acid, L-aspartic acid and kainic acid from osmotically sensitive membrane vesicles prepared from rat brain. L-Glutamic acid and L-aspartic acid showed the greatest efficacy for the stimulation of 22Na+ efflux with EC50 values of 3 microM. Kainic acid produced 28% of the maximal efflux seen with L-glutamic acid or L-aspartic acid with an EC50 value of 1.5 microM. Quisqualic acid never showed statistically significant increases in 22Na+ efflux over control experiments. N-Methyl-D-aspartic acid showed no detectable efflux activity in this preparation. DL-2-Amino-4-phosphonobutyric acid (APB) inhibited up to 40% of the 50 microM L-glutamic acid-stimulated or 50 microM L-aspartic acid-stimulated 22Na+ efflux with an IC50 value of 1.5 nM. Calcium was required for the inhibitory action of APB, but not for the stimulatory actions of L-glutamic, L-aspartic, or kainic acids. L-Glutamic, L-aspartic, and kainic acids at concentrations above 100 microM were found to inhibit rather than to stimulate 22Na+ efflux. Veratridine (1 microM) had no influence on the 22Na+ efflux component which was produced by L-glutamic or kainic acids. We are unable to firmly establish the mechanism for the stimulated 22Na+ efflux.

Animals↗
PubMed1969

Metabolism of Glutamic Acid and N-Acetylglutamic Acid in Leaf Discs and Cell-free Extracts of Higher Plants.

Radioactive glutamic acid and N-acetylglutamic acid have been incubated with normal and wilted leaf discs and radioactivity recovered in uncombined proline. The discs which had been placed under moisture stress incorporated considerably more label in uncombined proline than did normal discs.In extracts of swiss chard leaves, both (14)C-N-acetylglutamic acid and glutamic acid are metabolized to their corresponding semialdehyde as evidenced by a recovery of proline after appropriate treatment. There is also incorporation of label in N(a)-acetylornithine from N-acetylglutamic acid. These reactions require ATP, Mg(2+), and NADH or NADPH.

Journal Article↗
PubMed1996

Valproic acid differs in its in vitro effect on glutamic acid decarboxylase activity in neonatal and adult rat brain.

1. The in vitro effect of valproic acid (VA) (10(-6) to 10(-3) M) on glutamic acid decarboxylase (GAD) activity in whole brain and cerebral cortex (CC) of neonates and of adult rats was examined. 2. VA did not induce changes on GAD activity either in CC or in the rest of the brain (RB) of adult animals. 3. But at 10(-3) M, VA induced an increase in GAD activity in homogenates of noncortical brain areas of neonates; no increments were found in CC of these animals. This latter increase was detected in the membrane-bound fraction of the enzyme and was not due to physicochemical nonspecific changes related to the potential solvent activity of VA at this high concentration. 4. We may conclude that VA induces changes on GAD activity in neonatal stages of development but not in adult brain. Therefore, although a direct enhancement of GAD activity may play a role in the mechanism of action of VA in pediatric patients, this cannot be verified in the adult population.

Aging↗
PubMed1993

Human autoantibodies react with glutamic acid decarboxylase antigen in human and rat but not in mouse pancreatic islets.

The presence of one of the major targets for autoantibodies in Type 1 (insulin-dependent) diabetes mellitus, the enzyme glutamic acid decarboxylase, was studied in human, rat and mouse pancreatic tissue using immunoprecipitation and immunohistochemical techniques. Immunoprecipitation of glutamic acid decarboxylase was attempted with lysates of [35S]-methionine-labelled rat or mouse pancreatic islets using two different glutamic acid decarboxylase antisera, one mouse monoclonal antibody raised against the 65 kDa isoform of the enzyme, sera from six patients with Type 1 diabetes, one patient with stiff-man syndrome and sera from 19 non-obese diabetic mice. The same sera were used for immunoperoxidase staining of cryosections of human, rat or mouse pancreas. Using patient sera glutamic acid decarboxylase was detected by immunoprecipitations from isolated rat islets but not from islets of five different mouse strains tested, including the non-obese diabetic mouse. When using the non-obese diabetic mouse sera, glutamic acid decarboxylase could not be detected in either rat or mouse tissue. Immunoperoxidase staining demonstrated high levels of glutamic acid decarboxylase in human and rat pancreatic islets but low levels in mouse islets. Direct measurements of enzyme activity showed glutamic acid decarboxylase to be present in mouse islets at a level of about 40% of that in rat islets, and subsequent Western blot analyses indicated that mouse islets express the 67 kDa isoform, whereas as in rat islets both the 67 and 65 kDa isoforms are present.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Mechanism of the thesaurismosis and altered lysosomal dynamics induced by poly-D-glutamic acid in kidney proximal tubular cells.

In the companion paper, we report that a single injection of poly-D-glutamic acid causes an acute lysosomal storage condition and apparently impairs the lysosomal fission dynamics. The present paper addresses the mechanisms of these two alterations using a combination of in vivo and in vitro biochemical approaches. After a single intravenous injection, 14C-poly-D-glutamic acid was rapidly cleared from the plasma and appeared in the urine. Yet, a small but sizable fraction of the injected polymer was taken up by the kidney cortex through a saturable process (Kuptake, 150 mg/kg body wt; uptakemax 96 micrograms/g cortex). Analytical subcellular fractionation of cortex homogenates demonstrated that at initial stages, the 14C label was predominantly associated with subcellular particles of intermediate size and low equilibrium density, and was therefore slowly transferred to larger particles equilibrating at high density, then codistributing with the lysosomal hydrolases. At a concentration of 10 mg/ml (equivalent to its estimated concentration in lysosomes), poly-D-glutamic acid formed micronic aggregates ( > or = 10 microns) when brought to solution at pH < or = 6 in relation to its decreased ionization (pKa of lateral chains approximately equal to 4.25). Finally, 1 day after the injection of poly-D-glutamic acid, the activities of several lysosomal enzymes (hexosaminidase, cathepsin B, acid sphingomyelinase, and sulfatase B), but not of all of them (eg, acid phosphatase), were increased in the kidney cortex. We propose that poly-D-glutamic acid reaches lysosomes by adsorptive endocytosis and becomes concentrated within these organelles because its withstands hydrolysis until it forms aggregates or precipitates, causing a decrease in the fluidity or the deformability ("gelling") of the lysosomal matrix. This should alter the dynamics of intercommunication of these organelles by impairing their fission without a proportionate effect on their fusion properties. In addition, the data suggest that the presence of poly-D-glutamic acid directly or indirectly slows down the degradation of several lysosomal enzymes.

Animals↗
PubMed1986

Cardiorespiratory effects produced by microinjecting L-glutamic acid into medullary nuclei associated with the ventral surface of the feline medulla.

The purpose of our study was to use microinjections of L-glutamic acid to better localize the cell bodies in the intermediate area of the ventral medullary surface that exert control over cardiorespiratory activity. L-glutamic acid (200 nl of a 1-M solution) was microinjected into the nucleus paragigantocellularis lateralis, lateral reticular nucleus and into an area which is part of the 'glycine-sensitive area', which lies in the center of the intermediate area. Normally, when L-glutamic acid is applied to the surface of the intermediate area, increases in arterial pressure and tidal volume are observed. Increases in tidal volume were never observed upon microinjection into the 3 sites associated with the intermediate area, suggesting that the tidal volume change elicited from surface application occurs because of L-glutamic acid interacting with cell bodies either on the surface or extremely close to the surface. Pressor responses were elicited with microinjection of L-glutamic acid into the lateral reticular nucleus and the 'glycine-sensitive area', but not the nucleus paragigantocellularis lateralis; indeed, microinjection of L-glutamic acid into the nucleus paragigantocellularis lateralis caused hypotension. Hence, cell bodies responsible for raising arterial pressure may reside in either the lateral reticular nucleus or the 'glycine-sensitive area'.

Animals↗
PubMed1989

Glutamic acid-113 serves as the retinylidene Schiff base counterion in bovine rhodopsin.

The characteristic wavelength at which a visual pigment absorbs light is regulated by interactions between protein (opsin) and retinylidene Schiff base chromophore. By using site-directed mutagenesis, charged amino acids in bovine rhodopsin transmembrane helix C were systematically replaced. Substitution of glutamic acid-134 or arginine-135 did not affect spectral properties. However, substitution of glutamic acid-122 by glutamine or by aspartic acid formed pigments that were blue-shifted in light absorption (lambda max = 480 nm and 475 nm, respectively). While the substitution of glutamic acid-113 by aspartic acid gave a slightly red-shifted pigment (lambda max = 505 nm), replacement by glutamine formed a pigment that was strikingly blue-shifted in light absorption (lambda max = 380 nm). The 380-nm species existed in a pH-dependent equilibrium with a 490-nm species such that at acidic pH all of the pigment was converted to lambda max = 490 nm. We conclude that glutamic acid-113 serves as the retinylidene Schiff base counterion in rhodopsin. We believe that this opsin-chromophore interaction is an example of a general mechanism of color regulation in the visual pigments.

Amino Acid Sequence↗
PubMed1983

Enzymic resolution and binding to rat brain membranes of the glutamic acid agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid.

The enantiomers of the glutamic acid central nervous system receptor agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were prepared via kinetic resolution of the racemic N-acetylated 3-methoxy derivative by reusable, immobilized aminoacylase. L-AMPA was more effective (IC50 = 0.6 microM) than D-AMPA (IC50 = 4.8 microM) in displacing racemic [3H]AMPA from binding sites on rat brain synaptic membranes in agreement with their relative in vivo excitatory potencies.

Animals↗