Levels Of Glutamate Dehydrogenase Research Articles

Nitrate reductase, nitrite reductase and glutamate dehydrogenase levels in roots and leaves of maize seedlings

Total activities of nitrate and nitrite reductases were higher in 4 to 20 day old maize plants in the leaves than in the roots. The ratio of activities found in the leaves and in the roots respectively was much higher in the case of nitrate reductase than in the case of nitrite reductase. On the other hand higher glutamate dehydrogenase activity in the roots than in the leaves clearly indicates that the roots play a more important role in the assimilation of ammonium than in the assimilation of nitrate. When comparing the distribution of seminal and nodal adventitious roots of maize seedlings with the assimilation of inorganic nitrogen on the basis of enzyme levels, it could be deduced that during the first 20 days of seedling growth seminal roots were more involved in the assimilation of nitrate whereas nodal adventitious roots were more active in ammonium assimilation.

Physiological studies on the effects of nutritional imbalance on the central nervous system. II. Effects of thiamine deficiency on oxidative enzymes in the brain of chicken, Gallus domesticus.

The activitiy levels of succinate dehydrogenase, glutamate dehydrogenase and pyruvate dehydrogenase in the fore, mid and hind brain regions of the thiamine deficient chicken, Gallus domesticus were determined. The activity levels of succinate dehydrogenase and glutamate dehydrogenase in all the 3 regions of brain showed augmentation on inducing thiamine deficiency. In contrast the activity levels of pyruvate dehydrogenase decreased in the brain of thiamine deficient animals. It is suggested that these changes in the oxidative enzymes indicate disturbance caused in the operation of the tricarboxylic acid cycle in thiamine deficiency.

An elevated level of nadp-linked glutamate dehydrogenase is not a general feature of the caps of agaric sporophores

An elevated level of nadp-linked glutamate dehydrogenase is not a general feature of the caps of agaric sporophores

The regulation of ammonia assimilating enzymes in Lemma minor

Lemna minor has the potential to assimilate ammonia via either the glutamine or glutamate pathways. A 3-4 fold variation in the level of ferredoxindependent glutamate synthase may occur, when plants are grown on different nitrogen sources, but these changes show no simple relationship to changes in the endogenous pool of glutamate. High activities of glutamate synthase and glutamine synthetase at low ammonia availability suggests that these two enzymes function in the assimilation of low ammonia concentrations. Increasing ammonia availability leads to a reduction in level of glutamate synthase and glutamine synthetase and an increase in the level of glutamate dehydrogenase. Glutamine synthetase and glutamate dehydrogenase are subject to concurrent regulation, with glutamine rather than ammonia, exerting negative control on glutamine synthetase and positive control on glutamate dehydrogenase. The changes in the ratio of these two enzymes in response to the internal pool of glutamine could regulate the direction of the flow of ammonia into amino acids via the two alternative routes of assimilation.

Properties of glutamate dehydrogenase from Lemna minor

Sterile cultures of Lemna minor grown in the presence of either nitrate, ammonium or amino acids failed to show significant changes in glutamate dehydrogenase (GDH) levels in response to nitrogen source. Crude and partially purified GDH preparations exhibit NADH and NADPH dependent activities. The ratio of these activities remain ca 12:1 during various treatments. Mixed substrate and product inhibition studies as well as electrophoretic behaviour suggest the existence of a single enzyme which is active in the presence of both coenzymes. GDH activity was found to be localized mainly in mitochondria. Kinetic studies revealed normal Michaelis kinetics with most substrates but showed deviations with NADPH and glutamate. A Hill-coefficient of 1.9 determined with NADPH indicates positive cooperative interactions, whereas a Hill-coefficient of 0.75 found with glutamate may be interpreted in terms of negative cooperative interactions. NADH dependent activity decreases rapidly during gel filtration whereas the NAD + and NADPH activities remain unchanged. GDH preparations which have been pretreated with EDTA show almost complete loss of NADH and NAD + activities. NADPH activity again remains unaffected. NAD + activity is fully restored by adding Ca 2+ or Mg 2+, whereas the NADH activity can only be recovered by Ca 2+ but not at all by Mg 2+. Moderate inhibition of GDH reactions observed with various adenylates are fully reversed by adding Ca 2+, indicating that the adenylate inhibition is due solely to the chelating properties of these compounds.

Ammonium uptake and metabolism by mitrogen fixing bacteria. II. Klebsiella pneumoniae.

The primary steps of N2, ammonia and nitrate metabolism in Klebsiella pneumoniae grown in a continuous culture are regulated by the kind and supply of the nitrogenous compound. Cultures growing on N2 as the only nitrogen source have high activities of nitrogenase, unadenylated glutamine synthetase and glutamate synthase and low levels of glutamate dehydrogenase. If small amounts of ammonium salts are added continuously, initially only part of it is absorbed by the organisms. After 2-3 h complete absorption of ammonia against an ammonium gradient coinciding with an increased growth rate of the bacteria is observed. The change in the extracellular ammonium level is paralleled by the intracellular glutamine concentration which in turn regulates the glutamine synthesis and an induction of glutamate dehydrogenase synthesis. Upon deadenylation these events are reversed.--Addition of dinitrophenol causes transient leakage of intracellular ammonium into the medium.

Regulation of the ammonia assimilatory enzymes in Salmonella typhimurium

The regulation of glutamate dehydrogenase (EC 1.4.1.4), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 2.6.1.53) was examined for cultures of Salmonella typhimurium grown with various nitrogen and amino acid sources. In contrast to the regulatory pattern observed in Klebsiella aerogenes, the glutamate dehydrogenase levels of S. typhimurium do not decrease when glutamine synthetase is derepressed during growth with limiting ammonia. Thus, it appears that the S. typhimurium glutamine synthetase does not regulate the synthesis of glutamate dehydrogenase as reported for K. aerogenes. The glutamate dehydrogenase activity does increase, however, during growth of a glutamate auxotroph with glutamate as a limiting amino acid source. The regulation of glutamate synthase levels is complex with the enzyme activity decreasing during growth with glutamate as a nitrogen source, and during growth of auxotrophs with either glutamine or glutamate as limiting amino acids.

Regulation of Glutamate Dehydrogenase and Nitrate Reductase Levels in Excised Pea Roots by Exogeneously Supplied Sugar

The activities of NADH2 dependent glutamate dehydrogenase (GDH) and nitrate reductase were followed in excised pea roots cultured in liquid medium with or without sucrose. Whilst the persistance of nitrate reductase activity in excised pea roots depends directly on the presence of sugar in the medium and whilst in its absence nitrate reductase activity drops to the initial value before the induction with nitrate, both NADH9 dependent GDH and NADPH2 dependent GDH activities rise in excised pea roots in the absence of sugar in the medium, and vice versa, their activities are maintained at approximately the same level as in corresponding parts of roots on intact seedlings in the presence of sugar in the medium. The increase in NADH2 dependent GDH activity is inhibited by actidione which indicates that de novo synthesis of the enzyme is probably responsible for the increase. Glucose and fructose are in their effects equivalent to sucrose. The omission of sugar from the medium causes also a change in the ratio of the activities of individual isoenzymes of NAD+ dependent GDH. Physiological concentrations of ammonium and nitrate ions neither influence GDH level in the presence of sugar nor in the absence of it. The above mentioned sugars are apparently involved in the regulation of these enzymes directly and not indirectly by means of their metabolites formed during respiration. This is indicated by the results obtained in the experiments with exogenously supplied metabolites of glycolysis, pentose phosphate cycle and Krebs cycle, which did not show any significant effect on GDH and nitrate reductase levels. The increase in GDH level observed after the addition of sublethal concentrations of some respiratory inhibitors to the medium containing sugar was probably caused by decreased sugar uptake and transport. The regulation of GDH level controlled by sugars is in isolated pea roots independent of some other regulatory mechanisms (controlled by acids, nitrite and hydroxylamine), and vice versa. On the other hand, the results of our experiments indicate that the increase in the level of NADH2 dependent GDH observed by other authors in the roots of whole intact plants after their exposure to high concentrations of ammonium salts, may be, at least partly, caused indirectly by changes in the level of sugars in these roots.

The nature and control of the tricarboxylate cycle in beetle flight muscle.

The only exogenous substrates oxidized by mitochondria isolated from the flight muscle of the Japanese beetle (Popillia japonica) are proline, pyruvate and glycerol 3-phosphate. The highest rate of oxygen consumption is obtained with proline. The oxidation of proline leads to the production of more NH3 than alanine, indicating a functioning glutamate dehydrogenase (EC 1.4.1.2). Studies of mitochondrial extracts confirm the presence of a very active glutamate dehydrogenase, and this enzyme is found to be activated by ADP and inhibited by ATP. These extracts also show high alanine aminotransferase activity (EC 2.6.1.2) and a uniquely active "malic' enzyme (EC 1.1.1.39). The "malic' enzyme is activated by succinate and inhibited by ATP and by pyruvate. It is suggested that the input of tricarboxylate-cycle intermediate from proline oxidation is balanced by the formation of pyruvate from malate, and the complete oxidation of the majority of the pyruvate. Studies of the steady-state concentrations of mitochondrial CoASH and CoA thioesters during proline oxidation show a high succinyl (3-carboxypropionyl)-CoA content which falls on activating respiration with ADP. There is a concomitant rise in CoASH. However, the reverse transition, from state-3 to state-4 respiration, causes only very slight changes in acylation. The reasons for this are discussed. Studies of the mitochondrial content of glutamate, 2-oxoglutarate, malate, pyruvate, citrate and isocitrate during the same phases of proline oxidation give results consistent with control at the level of glutamate dehydrogenase and isocitrate dehydrogenase during proline oxidation, with the possibility of further control at "malic' enzyme. During the oxidation of pyruvate all of the tricarboxylate-cycle intermediates and NAD(P)H follow the pattern of changes described in the blowfly (Johnson & Hansford, 1975; Hansford, 1974) and isocitrate dehydrogenase is identified as the primary site of control.?2OAuthor

Regulation of glutamate dehydrogenase level in excised pea roots by some exogenously supplied compounds with auxin activity

Besides IAA, other compounds with auxin activity (of both indole and non-indole nature) can also cause an increase in glutamate dehydrogenase level in excised pea roots. The effect of these substances is probably not mediated by ethylene, depends on proteosynthesis, is independent of the regulatory effect of sugars and need not be influenced by the antagonism between auxins and cytokinins.

The Effect of Promezathine Hydrochloride on the Development and Pathogenicity of Fasciola Hepatica in the Sheep

The development and pathogenicity of Fasciola hepatica was compared in promezathine-treated and untreated groups of sheep. The treated group showed delayed onset of circulatory eosinophilia and liveweight loss, consistently lower levels of plasma glutamate dehydrogenase, and, at 8 to 10 weeks after infection, a lower loss of 51 Cr-labelled plasma in the faeces. At post-mortem examination, the treated sheep showed a less severe hepatitis, the flukes were of greater mean length, and there was evidence of delayed entry to the bile ducts. Fluke recoveries were similar in the two groups. On compara le développement et la pathologie de Fasciola hepatica chez des groupes de moutons traités et non traités par la prométhazine. Le groupe traité révéla une atteinte retardée des éosinophiles circulants et une perte de poids, des taux nettement plus bas de déshydrogénase glutamique plasmatique, et, au bout de 8 à 10 semaines d’infection, une perte moindre de plasma marqué au Cr 51 radioactif au niveau du fécès. A l’examen post-mortem, les moutons traités étaient porteurs d’une hépatite moins sévère, les lobes étaient d’une taille moyenne plus grande, et il existait un retard de sécretion dans les canaux biliaires. Les lobes retrouvaient un aspect normal de façon similaire dans les deux groupes. Doc Entwicklung und pathogene Wirkung von Fasciola hepatica bei Promezathin behandelten und nicht behandelten Gruppen von Schafen werden verglichen. Bei der behandelten Gruppe traten Eosinophilie, Gewichtsabnahme und beständige geringere Konzentrationen von Plasmaglutamathydrogenase später auf und 8–10 Wochen nach der Infektion ein geringer Verlust von durch 51 Cr gekennzeichnetem Plasma in den faeces. Bei der Sektion zeigte sich die Hepatitis der behandelten Schafe als weniger schwer, die Schmarotzer waren im Durchschnitt länger und man konnte sehen, dass sie erst später in die Gallengänge eingewandert waren. Bei beiden Gruppen konnte eine ähnliche Menge von Würmern gewonnen werden. Se comparó el crecimiento y patogeneicidad de la Fasciola hepatica en dos grupos de corderos uno tratado con promezatina y otro no. El grupo tratado mostró un retraso en la aparición de eosinofilia y en la pérdida de peso, niveles consistentemente más bajos de dehidrogenasa glutámica en plasma y, a las 8–10 semanas después de la infección, una menor pérdida de Cr 51 etiquetado en plasma por las heces. En el examen post-mortem, los corderos tratado mostraron un grado de hepatitis menos grave, las duelas eran de un tamaño medio mayor y se observó evidencia de un retraso en la penetración en los conductos biliares. Las recuperaciones de duelas fueron similares en embos grupos.

The participation of the anabolic glutamate dehydrogenase in the nitrogen catabolite repression of arginase in Saccharomyces cerevisiae.

Arginase synthesis appears to be under the control of at least two distinct processes. In addition to substrate induction which operates through a Jacob and Monod mechanism, one may define a process of nitrogen catabolite repression which is a part of the ammonium effect. The two processes show a large degree of independence most specifically shown by mutations which independently cancel each of the two mechanisms without affecting the gross physiology. In this line we show that controversial conclusions can be reached when using different approaches to provoke catabolite derepression. The nitrogen catabolite repression is abolished by the gdhA− mutation which affects the structural gene for the NADP-specific glutamate dehydrogenase. The effect of the gdhA− mutation is retained when the metabolic defect is compensated by addition of glutamate as well as the best nitrogen nutrients, glutamine and asparagine. This control of arginase and of some, but not all, other nitrogen catabolic enzymes may operate at constant levels of glutamate dehydrogenase (NADP). It occurs when the glutamate dehydrogenase (NADP) is in its catalytically active state, which requires the simultaneous presence of two substrates, NH+4 and 2-oxoglutarate. In fungi the glutamate dehydrogenase (NADP) is the first enzyme of the assimilatory pathway of ammonium, which, when functioning, makes arginase unnecessary. However the regulatory function seems to operate by an intrinsic modification of the enzyme itself rather than by the result of its catalytic action. Carbon catabolite repression appears largely independent from nitrogen catabolite repression and vice versa. However, arginase synthesis is enhanced in mutants lacking aconitase as well as by very poor carbon nutrition. Both conditions decrease the level of 2-oxoglutarate which is required for the expression of nitrogen catabolite repression. Once specific induction and nitrogen catabolite repression are clearly defined, it becomes possible to show that additional regulatory processes are involved in arginase sythesis (Wiame, 1973).

Mechanism of ammonia assimilation in streptococci.

SUMMARY: Streptococcus sanguis, S. bovis, S. mutans and S. salivarius, and also Escherichia coli for comparison, were grown separately in a chemostat under ammonia- and glucose-limitation. Bacterial extracts were assayed for ammonia-assimilating enzymes. For E. coli the level of glutamate dehydrogenase decreased and the levels of glutamine synthetase and glutamine (amide): 2-oxoglutarate aminotransferase (glutamate synthase) increased following a change from glucose- to ammonia-limitation. In contrast, ammonia-limited streptococci contained much higher levels of glutamate dehydrogenase than glucose-limited streptococci, and although a glutamine synthetase was detected in S. bovis, glutamate synthase could not be detected in any of the streptococci. Low activity of a NAD-linked alanine dehydrogenase was found in S. bovis and S. sanguis. These results suggest that the only pathway of ammonia assimilation in streptococci involves glutamate dehydrogenase, irrespective of the nature of the growth limitation. Glutamate dehydrogenase extracted from the different species of Streptococcus had similar Michaelis constants and optimum pH values.

Relationship of glutamate dehydrogenase levels to free amino acids, amides and ammonia in excised oat leaves

Relationship of glutamate dehydrogenase levels to free amino acids, amides and ammonia in excised oat leaves

Regulation of the Synthesis of Enzymes Responsible for Glutamate Formation in Klebsiella aerogenes

Abstract A mutant of Klebsiella aerogenes lacking glutamine (amide):α-ketoglutarate (NADP+) amidotransferase oxidoreductase (glutamate synthetase) cannot grow in minimal media containing ammonia as the only nitrogen source at a concentration lower than 1 mm. In addition, in a glucose containing medium, it fails to utilize amino acids, such as histidine, that are converted to glutamate, as sources of nitrogen. It can use glutamate as source of nitrogen. Revertants were isolated capable of growth on glucose-histidine, but unable to use ammonia. These revertants still lack glutamate synthetase, but produce glutamine synthetase constitutively (glnC-). They fail to produce glutamate dehydrogenase, and thus cannot use ammonia as a nitrogen source. An analysis of the levels of glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase in the parent organism, in mutants lacking glutamine synthetase, and in mutants producing it constitutively, reveals that glutamine synthetase represses the formation of glutamate dehydrogenase. A lack of glutamate synthetase appears to interfere with the derepression of glutamine synthetase. On the other hand, the loss of glutamate dehydrogenase by mutation does not affect glutamine synthetase. These results, together with those reported in an earlier paper (Prival, M. J., Brenchley, J. E., and Magasanik, B. (1973) J. Biol. Chem. 248, 4334–4344), indicate that glutamine synthetase is the key element in the regulation of the synthesis of enzymes capable of supplying the cell with glutamate.

Ammonia assimilation in blue-green algae.

The occurrence of alanine dehydrogenase (AlaDH), glutamate dehydrogenase (GDH), and 2-ketoglutarate: glutamine amidotransferase (GGAT), has been surveyed in a number of blue-green algae. Among nine unicellular strains grown with nitrate, and belonging to five of the major typological groups, AlaDH was present in seven, and GDH in all eight that were assayed. In ten filamentous strains grown with nitrate, and belonging to the three nonheterocyst-forming and four heterocyst-forming groups, AlaDH was present in six, but both AlaDH and GDH were present in only one strain. In those strains which could be grown with N2 as sole nitrogen source, levels of GDH were generally lower, and AlaDH higher in cells fixing N2 than in those growing with nitrate. GGAT was undetectable in N2-grown cells. Two unicellular and three filamentous strains were tested for their ability to use L-alanine, L-glutamate, L-glutamine, and L-asparagine as sole sources of nitrogen. Of these, L-asparagine was utilized most effectively. There was little difference in levels of GDH in cells grown with nitrate or with L-asparagine, while the levels of AlaDH were slightly lower in cells grown with L-asparagine.

Adenosine 3':5'-cyclic monophosphate control of the enzymes of glutamine metabolism in Escherichia coli.

The effect of cAMP on the intracellular levels of five enzymes concerned with the interconversion of glutamate and glutamine in E. coli has been examined. Cyclic AMP added to the culture medium increases the levels of glutamate dehydrogenase (EC 1.4.1.4) and glutamine synthetase (EC 6.3.1.2); it decreases the levels of glutamate synthase (EC 1.4.1.X), and glutaminase A (EC 3.5.1.2). Cyclic AMP did not affect the level of glutaminase B (EC 3.5.1.2). These alterations in enzyme levels by cAMP require cyclic AMP receptor protein, since the levels of these enzymes were unchanged by cAMP in a mutant lacking this receptor. Chloramphenicol also abolished the effects of cAMP, a result that implies protein synthesis is necessary for these changes in enzyme levels to occur. The reciprocal effects of cAMP on the levels of these enzymes may play an important role in the cellular regulation of nitrogen metabolism.

Enzyme studies with the livers of chicks fed semi-synthetic diets containing crystalline amino acids and diammonium citrate.

Synopsis The levels of glutamate dehydrogenase [NAD(P)], (GDH), aspartate trans‐aminase (AspT) and alanine transaminase (AlT) were measured in livers from chicks fed on a semi‐synthetic diet containing crystalline essential amino acids as the sole nitrogen source (diet A). The effects of a supplement of 12.0% glutamic acid (diet H) or 11.07% diammonium citrate (DAC) (diet B) or 12.0% glutamic acid plus 1.0% proline with an additional 0.6% glycine (diet C) on these enzymes were studied and the results compared with the levels found for control chicks given a typical diet based on cereal protein (diet J). The abilities of livers from chicks given diets A, B and C to synthesise [14C] glutamic acid from [14C]2‐oxoglutaric acid and diammonium citrate (DAC) were assessed. The levels of GDH, AspT and AlT found in the livers of chicks given the control diet were 54.1, 966 and 123.7 units/mg protein respectively. Non‐essential nitrogen added as glutamic acid or as DAC did not cause induction of the enzymes studied...

Purification and properties of alpha-ketoglutarate reductase from Micrococcus aerogenes.

Micrococcus aerogenes grown in media containing glutamate has high levels of glutamate dehydrogenase and alpha-ketoglutarate reductase. The latter enzyme catalyzes the reversible reduction of alpha-ketoglutarate to alpha-hydroxyglutarate in the presence of reduced nicotinamide adenine dinucleotide (NADH). The enzyme has a high specificity for both substrates in either direction and displays Michaelis-Menten kinetics at moderate substrate concentrations. K(m) values of 0.12 to 0.17 mm alpha-ketoglutarate and 0.3 mm NADH for the forward reaction were calculated from data obtained at low substrate concentrations. At high concentrations, this reaction was inhibited by both substrates. The reverse reaction, which proceeded at 0.1 to 0.2 times the rate of the forward reactions, was inhibited by one of the products, alpha-ketoglutarate. K(m) values for the substrates of this reaction were 10 mm for alpha-hydroxyglutarate and 1 mm for nicotinamide adenine dinucleotide. alpha-Ketoglutarate reductase has a molecular weight of 7.5 x 10(4) to 8.2 x 10(4) and is composed of identical polypeptide chains with a molecular weight of 3.6 x 10(4) to 3.8 x 10(4).

The mechanism of ammonia assimilation in nitrogen fixing Bacteria.

Enzymatic and genetic evidence are presented for a new pathway of ammonia assimilation in nitrogen fixing bacteria: ammonium → glutamine → glutamate. This route to the important glutamate-glutamine family of amino acids differs from the conventional pathway, ammonium → glutamate → glutamine, in several respects. Glutamate synthetase [(glutamine amide-2-oxoglutarate aminotransferase) (oxidoreductase)], which is clearly distinct from glutamate dehydrogenase, catalyzes the reduced pyridine nucleotide dependent amination of α-ketoglutarate with glutamine as amino donor yielding two molecules of glutamate as product. The enzyme is completely inhibited by the glutamine analogue DON, whereas glutamate dehydrogenase is not affected by this inhibitor; the glutamate synthetase reaction is irreversible. Glutamate synthetase is widely distributed in bacteria; the pyridine nucleotide coenzyme specificity of the enzyme varies in many of these species. The activities of key enzymes are modulated by environmental nitrogenous sources; for example, extracts of N2-grown cells of Klebsiella pneumoniae form glutamate almost exclusively by this new route and contain only trace amounts of glutamate dehydrogenase activity whereas NH3-grown cells possess both pathways. Also, the biosynthetically active form of glutamine synthetase with a low K m for ammonium predominates in the N2-grown cell. Several mutant strains of K. pneumoniae have been isolated which fail to fix nitrogen or to grow in an ammonium limited environment. Extracts of these strains prepared from cells grown on higher levels of ammonium have low levels of glutamate synthetase activity and contain the biosynthetically inactive species of glutamine synthetase along with high levels of glutamate dehydrogenase. These mutants missing the new assimilatory pathway have serious defects in their metabolism of many inorganic and organic nitrogen sources; utilization of at least 20 different compounds is effected. We conclude that the new ammonia assimilatory route plays an important role in nitrogenous metabolism and is essential for nitrogen fixation.