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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↗
PubMedDate not supplied

Comparison of the effects of leucines, non-metabolizable leucine analogues and other insulin secretagogues on the activity of glutamate dehydrogenase.

Glutamate dehydrogenase (GLDH) from bovine liver was employed in model system for testing a possible role of GLDH in insulin release. The ability of different insulin secretagogues to stimulate the activity of the diethylstilbestrol-inhibited enzyme was tested. The two insulin-releasing amino acids, L-leucine and its non-metabolizable analogue 2-aminobicyclo(2, 2, 1)heptane-2-carboxylic acid [b(--)-BCH], were the best stimulators of GLDH activity. The non-secreting stereoisomers, D-leucine and b(+)-BCH, were less effective. Glucose, L-arginine and the leucine metabolite alpha-ketoisocaproic acid lacked significant effects on GLDH activity. Small and diverging effects were obtained with sulfonvlurea compounds: whereas carbutamide caused slight stimulation, tolbutamide and glipizide had no effect, and glibenclamide was an inhibitor. The specificity of the insulin-releasing amino acids L-leucine and b(--)-BCH in stimulating GLDH activity makes it tempting to speculate about a connection between allosteric regulation of pyridine nucleotide-dependent enzymes and insulin release.

Amino Acids↗
PubMed1984

Neurological disorders associated with deficiency of glutamate dehydrogenase.

Glutamate dehydrogenase (GDH) activity was measured in leukocytes from 88 patients with various types of degenerative neurological disorders affecting primarily the cerebellum and/or the basal ganglia, and 26 healthy control subjects. Twelve patients with slowly progressive multiple-system atrophic disorders were found to have a partial deficiency of this enzyme (52% of control level). The majority of these patients evidenced a constellation of neurological findings consistent with the diagnosis of olivopontocerebellar atrophy, although others were atypical in their neurological manifestations. Thus, GDH-deficient patients were encountered with predominantly extrapyramidal manifestations (atypical Parkinson's disease), cerebellar dysfunction with peripheral neuropathy, or anterior horn cell signs, suggesting that a pleomorphic phenotypic expression of the enzymatic deficiency may occur. Seven cases of GDH deficiency were familial and 5 were sporadic. The former patient group consisted of siblings of either sex, but no parents or offspring were affected. The genetic pattern of the disorder is compatible with autosomal recessive inheritance. Patients with dominantly inherited olivopontocerebellar atrophy or other types of cerebellar or basal ganglia degenerative neurological disorders showed normal GDH activity. Leukocyte GDH was fractionated into "particulate-heat labile" and "soluble-heat stable" components. In the patients the decrease in activity was limited to the "particulate-heat labile" component. A genetic mutation of a GDH "isoenzyme" may occur in some patients with multiple-system degeneration.

Adult↗
PubMed1997

Enzymes in antarctic fish: glucose-6-phosphate dehydrogenase and glutamate dehydrogenase.

Glucose-6-phosphate dehydrogenase (G6PD) and L-glutamate dehydrogenase (GDH) from Antarctic fish were isolated and characterized. G6PD was purified from the erythrocytes of red-blooded Dissostichus mawsoni and from the colorless blood of the icefish Chionodraco hamatus. Structural and functional characterization showed that the two enzymes do not differ significantly from each other. GDH was purified from the liver of the icefish Chaenocephalus aceratus. As in other fish ODHs, it showed a marked preference for NAD-. The amino acid sequence of the active-site peptide is virtually identical to that of other fish and vertebrate counterparts. Although the basic structural features of the Antarctic enzymes are similar to those of mesophilic organisms, some catalytic and thermodynamic properties make the Antarctic enzymes more suited to cold-adapted organisms.

Amino Acid Sequence↗
PubMed1976

Studies of glutamate dehydrogenase. Regulation of glutamate dehydrogenase from Candida utilis by a pH and temperature-dependent conformational transition.

Glutamate dehydrogenase from Candida utilis undergoes a reversible conformational transition between an active and an inactive state at low pH AND low temperature. This conformational transition can also be followed by fluorescence measurements. The temperature-dependent equilibrium between the active and the inactive state is characterized by a transition temperature of 10.7 degrees C and a delta H value of 148 kcal/mol (620 kJ/mol). The temperature dependence of the enzymic activity above 15 degrees C yields an activation energy of 15 kcal/mol (63 kJ/mol), a larger value than that for the beef liver enzyme (9 kcal/mol; 38 kJ/mol). In contrast to the yeast enzyme the Arrhenius plot is linear and, therefore, the beef liver enzyme is not transformed into an inactive conformation at low temperatures. Sedimentation analysis shows that the inactivation of the Candida utilis enzyme is not caused by change in the quaternary structure. The pH dependence of the conformational transition at low pH measured by fluorescence change is characterized by a pK value of 7.01 for the enzyme in the absence and of 6.89 for the enzyme in the presence of 2-oxoglutarate with a Hill coefficient of 3.4 in both cases. Similar results are found when the pH dependence of the enzymic activity is analyzed. With the beef liver enzyme the same pK value is obtained but with a Hill coefficient of 1 indicating cooperativity only in the case of the Candida utilis enzyme. The best fit of the pH dependence of the rate constants of the fluorescence changes was obtained with pK values of 7.45 and 6.45 for the active and the inactive state respectively. In this model the lowest time constant which is obtained at the pH of the equilibrium was found to be 0.05 s-1. Preincubation experiments with the substrate 2-oxoglutarate but not with the coenzyme shift the equilibrium to the active conformation. The coenzyme obviously reduces the rate constant of the conformational transition. The sedimentation coefficient (SO20, w) and the molecular weight were found to be 11.0 S and 276 000, respectively. The enzyme molecule is built up by six polypeptide chains each having a molecular weight of 47 000.

Binding Sites↗
PubMed1969

Kinetic studies of glutamate dehydrogenase with glutamate and norvaline as substrates. Coenzyme activation and negative homotropic interactions in allosteric enzymes.

1. Kinetic studies of glutamate dehydrogenase were made with wide concentration ranges of the coenzymes NAD(+) and NADP(+) and the substrates glutamate and norvaline. Initial-rate parameters were evaluated. 2. Deviations from Michaelis-Menten behaviour towards higher activity were observed with increasing concentrations of either coenzyme with glutamate as substrate, but not with norvaline as substrate. 3. In phosphate buffer, pH7.0, Lineweaver-Burk plots with either coenzyme as variable and a constant, large glutamate concentration showed three or four linear regions of different slope with relatively sharp discontinuities. Maximum rates obtained by extrapolation and Michaelis constants for the coenzymes increased in steps with increase of coenzyme concentration. 4. In the absence of evidence of heterogeneity of the enzyme and coenzyme preparations, the results are interpreted in terms of negative homotropic interactions between the enzyme subunits. It is suggested that sharp discontinuities in Lineweaver-Burk plots or reciprocal binding plots may be characteristic of this new type of interaction, which can be explained in terms of an Adair-Koshland model, but not by the model of Monod, Wyman & Changeux.

Binding Sites↗
PubMed2001

Photorespiration-dependent increases in phospho enolpyruvate carboxylase, isocitrate dehydrogenase and glutamate dehydrogenase in transformed tobacco plants deficient in ferredoxin-dependent glutamine-alpha-ketoglutarate aminotransferase.

The metabolic cross-talk associated with re-assimilation of photorespiratory NH4+ was analysed in transformed tobacco (Nicotiana tabacum L.) plants with low activities of ferredoxin-dependent glutamine-alpha-ketoglutarate aminotransferase (Fd-GOGAT; EC 1.4.7.1). Amounts of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) protein and Rubisco transcripts were similar in all lines whether photorespiration rates were low (4,000 microl l(-1) CO2) or high (air). Leaf sucrose, hexose and starch contents were similar in all lines. In contrast, there was evidence that anaplerotic carbon flow was stimulated in the transformed lines with less than 60% Fd-GOGAT, since phospho enolpyruvate carboxylase (PEPc) activity and (PEPc) protein were increased. A strong positive correlation between leaf PEPc activity and glutamine accumulation was observed, suggesting that the increase in PEPc was related to the accumulation of glutamine. A modest stimulation of total NADP-isocitrate dehydrogenase (ICDH; EC 1.1.1.42) activity was also observed in the transformed lines with less than 60% Fd-GOGAT. This was accompanied by increases in both the cytosolic ICDH and mitochondrial NAD-isocitrate dehydrogenases (IDH; EC 1.1.1.41). IDH protein was also increased in the transformed plants with low Fd-GOGAT, suggesting that both IDH and ICDH are involved in the production of carbon skeletons (and ultimately alpha-ketoglutarate) necessary for the re-assimilation of NH4+. In contrast, PEPc, ICDH and IDH transcripts were similar in all lines. The aminating (but not the de-aminating) activity of NAD(H)-glutamate dehydrogenase (NAD(H)-GDH; EC 1.4.1.2) was greatly increased in plants with less than 60% of Fd-GOGAT after transfer to air. The data confirm that NH4+ or glutamine are involved in signalling, leading to modified gene expression and enzyme activity required for enhanced production of the C skeletons, to accommodate increases in the assimilation of photorespiratory NH4+. In addition, we provide the first demonstration of a compensatory role for NAD(H)-GDH in stabilising the leaf glutamic acid pool when Fd-GOGAT becomes limiting.

Amino Acid Oxidoreductases↗
PubMed1994

Purification and characterization of NADP-specific alcohol dehydrogenase and glutamate dehydrogenase from the hyperthermophilic archaeon Thermococcus litoralis.

Thermococcus litoralis is a strictly anaerobic archaeon that grows at temperatures up to 98 degrees C by fermenting peptides. Little is known about the primary metabolic pathways of this organism and, in particular, the role of enzymes that are dependent on thermolabile nicotinamide nucleotides. In this paper we show that the cytoplasmic fraction of cell extracts contained NADP-specific glutamate dehydrogenase (GDH) and NADP-specific alcohol dehydrogenase (ADH) activities, neither of which utilized NAD as a cofactor. The GDH is composed of identical subunits having an M(r) of 45,000 and had an optimal pH and optimal temperature for glutamate oxidation of 8.0 and > 95 degrees C, respectively. Potassium phosphate (60 mM), KCl (300 mM), and NaCl (300 mM) each stimulated the rate of glutamate oxidation activity between two- and threefold. For glutamate oxidation the apparent Km values at 80 degrees C for glutamate and NADP were 0.22 and 0.029 mM, respectively, and for 2-ketoglutarate reduction the apparent Km values for 2-ketoglutarate, NADPH, and NH4+ were 0.16, 0.14, and 0.63 mM, respectively. This enzyme is the first NADP-specific GDH purified form a hyperthermophilic organism. T. litoralis ADH is a tetrameric protein composed of identical subunits having an M(r) of 48,000; the optimal pH and optimal temperature for ethanol oxidation were 8.8 and 80 degrees C, respectively. In contrast to GDH activity, potassium phosphate (60 mM), KCl (0.1 M), and NaCl (0.3 M) inhibited ADH activity, whereas (NH4)2SO4 (0.1 M) had a slight stimulating effect. This enzyme exhibited broad substrate specificity for primary alcohols, but secondary alcohols were not oxidized.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Dehydrogenase↗
PubMed2005

Localization of NAD-isocitrate dehydrogenase and glutamate dehydrogenase in rice roots: candidates for providing carbon skeletons to NADH-glutamate synthase.

In rice roots, transient and cell-type-specific accumulation of both mRNA and protein for NADH-dependent glutamate synthase (NADH-GOGAT) occurs after the supply of NH(4) (+) ions. In order to better understand the origin of 2-oxoglutarate for this reaction, we focused on mitochondrial NAD-dependent isocitrate dehydrogenase (IDH) and glutamate dehydrogenase (GDH) in rice roots. Six rice cDNAs encoding a single catalytic (OsIDHa) and two regulatory (OsIDHc;1, OsIDHc;2) IDH subunits and three GDH proteins (OsGDH1-3) were isolated. These genes, except OsGDH3, were expressed in the roots. Real-time PCR analysis showed that OsIDHa and OsIDHc;1 transcripts, but not OsGDH1 and OsGDH2 transcripts, accumulated in a similar manner to NADH-GOGAT mRNA along the crown roots after the supply of different forms of inorganic nitrogen. Furthermore, immunolocalization studies revealed the NH(4) (+) induction of IDHa protein in two cell layers of the root surface, i.e. epidermis and exodermis, where NADH-GOGAT also accumulated. The possible relationship between NADH-GOGAT, IDH and GDH is discussed.

Amino Acid Sequence↗
PubMed2000

Salinity induced behavioural changes in malate dehydrogenase and glutamate dehydrogenase activities in rice seedlings of differing salt tolerance.

The activities of malate dehydrogenase in whole tissue extract (NAD(+)-MDH) as well as in mitochondrial (NAD(+)-MDH) and chloroplastic (NADP(+)-MDH) preparations of aminating (NADH-GDH) and deaminating(NAD(+)-GDH) glutamate dehydrogenases were studied in two sets of rice cultivars differing in salt tolerance grown under moderate (7 dS m(-1)) and high (14 dS m(-1)) NaCl salinity levels. A contrasting response to salinity on enzyme activities was found between the sensitive and tolerant cultivars during a 5-20-day growth period of study. NaCl salinity in situ caused increase in all three MDH activities in salt tolerant cvs. CSR-1 and CSR-3 whereas in salt sensitive cvs. Ratna and Jaya 16-100% inhibition in activities was noted. Chloroplastic MDH was extremely sensitive to NaCl. In seedlings of salt tolerant cultivars concomitant increase in both aminating and deaminating GDH activities was observed with increase in salinity level, whereas in sensitive cultivars under higher salinity level decrease in GDH activity was noted. Under in vitro conditions NaCl concentration in the range 1-1000 mM caused gradual inhibition in MDH activity. With 400 mM NaCl in vitro, complete loss of mitochondrial and chloroplastic MDH activities was observed. GDH activity increased with increasing concentration of NaCl up to 200 mM NaCl and other salts in vitro and was inhibited thereafter. However 800 mM NaCl caused complete loss of deaminating GDH activity from sensitive cultivar but not from tolerant cultivar. Results suggest varying behaviour of MDH and GDH in two sets of rice cultivars differing in salt tolerance and that inhibition in the activities of dehydrogenases in salt sensitive rice cultivars due to salinity may be one of the possible reasons for decreased growth of rice plants under saline conditions.

Journal Article↗
PubMed1993

Lactate dehydrogenase and glutamate dehydrogenase activities in the circumventricular organs of rat brain following neonatal monosodium glutamate.

Glutamate (glu) an excitatory neurotransmitter amino acid, is present in high concentrations in the mammalian central nervous system and is the most abundant amino acid in our daily diet. In the present study the activities of lactate dehydrogenase (LDH) and glutamate dehydrogenase (GDH) were evaluated in the circumventricular organs (CVO) of the brain in 25-day-old rats following MSG administration at a dose of 4 mg/g b.wt during the first ten days of life. The results show the LDH activity increased to 265% of that in the control (p < 0.001), whereas GDH activity was significantly decreased (p < 0.05). The great elevation in LDH, a cytoplasmic marker enzyme, is apparently due to cytoskeletal changes brought about as a consequence of glu toxicity, whereas lowered GDH activity indicates altered glu homostasis in the blood-brain-barrier deficient areas following neonatal exposure to glu.

Animals↗
PubMed2006

Tobacco isoenzyme 1 of NAD(H)-dependent glutamate dehydrogenase catabolizes glutamate in vivo.

Glutamate (Glu) dehydrogenase (GDH, EC 1.4.1.2-1.4.1.4) catalyzes in vitro the reversible amination of 2-oxoglutarate to Glu. The in vivo direction(s) of the GDH reaction in higher plants and hence the role(s) of this enzyme is unclear, a situation confounded by the existence of isoenzymes comprised totally of either GDH beta- (isoenzyme 1) or alpha- (isoenzyme 7) subunits, as well as another five alpha-beta isoenzyme permutations. To clarify the in vivo direction of the reaction catalyzed by GDH isoenzyme 1, [(15)N]Glu was supplied to roots of two independent transgenic tobacco (Nicotiana tabacum) lines with increased isoenzyme 1 levels (S4-H and S49-H). The [(15)N]ammonium (NH(4)(+)) accumulation rate in these lines was elevated approximately 65% compared with a null segregant control line, indicating that isoenzyme 1 catabolizes Glu in roots. Leaf glutamine synthetase (GS) was inhibited with a GS-specific herbicide to quantify any contribution by GDH toward photorespiratory NH(4)(+) reassimilation. Transgenic line S49-H did not show enhanced resistance to the herbicide, indicating that the large pool of isoenzyme 1 in S49-H leaves was unable to compensate for GS and suggesting that isoenzyme 1 does not assimilate NH(4)(+) in vivo.

Glutamate Dehydrogenase (NADP+)↗