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PubMed2003

Ammonia removal from wastewater by ion exchange in the presence of organic contaminants.

The scope of this study was the removal of ammonium by ion exchange from simulated wastewater. The study looks at the effect of organics upon ammonium ion exchange equilibrium uptake. The ion exchangers included a natural zeolite clinoptilolite, and two polymeric exchangers, Dowex 50w-x8, and Purolite MN500. The organic compounds studied included citric acid and a number of proteins. The traditional method for removal of ammonium and organic pollutants from wastewater is biological treatment, but ion exchange offers a number of advantages including the ability to handle shock loadings and the ability to operate over a wider range of temperatures. The results show that in most of the cases studied, the presence of organic compounds enhances the uptake of ammonium ion onto the ion exchangers.

Ammonia↗
PubMed2002

Ammonia-induced extracellular accumulation of taurine in the rat striatum in vivo: role of ionotropic glutamate receptors.

Accumulation of taurine (Tau), glutamate (Glu) and glutamine (Gln) was measured in vivo in microdialysates of the rat striatum following a direct application to the microdialysis tube of 60 mM ammonium chloride which renders the final ammonia concentration in the extracellular space to approximately 5 mM. The following compounds were coadministered with ammonia to distinguish between the different mechanisms that may underlie the accumulation of amino acids: ion transport inhibitors, diisothiocyanostilbene-2,2'-disulfonate (DIDS) and furosemide, a Glu transport inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (PDC), an NMDA receptor antagonist dizocilpine (MK-801) and an 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate (KA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). Ammonia stimulated Tau accumulation in the microdialysates to approximately 250% of the basal value. Furosemide did not significantly affect the stimulation by ammonia and DIDS only moderately depressed the effect. The ammonia-dependent Tau accumulation was increased by approximately 50% in the presence of PDC and reduced by approximately 35% in the presence dizocilpine and DNQX. In the microdialysates ammonia stimulated Glu and Gln accumulation somewhat less than Tau accumulation. Except for stimulation of Gln accumulation by DNQX, the effects were not modified by any of the cotreatments. The results are consistent with the assumption that ammonia stimulates Tau efflux mainly via activation of ionotropic Glu receptors.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Discovery of the ammonium substrate site on glutamine synthetase, a third cation binding site.

Glutamine synthetase (GS) catalyzes the ATP-dependent condensation of ammonia and glutamate to yield glutamine, ADP, and inorganic phosphate in the presence of divalent cations. Bacterial GS is an enzyme of 12 identical subunits, arranged in two rings of 6, with the active site between each pair of subunits in a ring. In earlier work, we have reported the locations within the funnel-shaped active site of the substrates glutamate and ATP and of the two divalent cations, but the site for ammonia (or ammonium) has remained elusive. Here we report the discovery by X-ray crystallography of a binding site on GS for monovalent cations, Tl+ and Cs+, which is probably the binding site for the substrate ammonium ion. Fourier difference maps show the following. (1) Tl+ and Cs+ bind at essentially the same site, with ligands being Glu 212, Tyr 179, Asp 50', Ser 53' of the adjacent subunit, and the substrate glutamate. From its position adjacent to the substrate glutamate and the cofactor ADP, we propose that this monovalent cation site is the substrate ammonium ion binding site. This proposal is supported by enzyme kinetics. Our kinetic measurements show that Tl+, Cs+, and NH4+ are competitive inhibitors to NH2OH in the gamma-glutamyl transfer reaction. (2) GS is a trimetallic enzyme containing two divalent cation sites (n1, n2) and one monovalent cation site per subunit. These three closely spaced ions are all at the active site: the distance between n1 and n2 is 6 A, between n1 and Tl+ is 4 A, and between n2 and Tl+ is 7 A. Glu 212 and the substrate glutamate are bridging ligands for the n1 ion and Tl+. (3) The presence of a monovalent cation in this site may enhance the structural stability of GS, because of its effect of balancing the negative charges of the substrate glutamate and its ligands and because of strengthening the "side-to-side" intersubunit interaction through the cation-protein bonding. (4) The presence of the cofactor ADP increases the Tl+ binding to GS because ADP binding induces movement of Asp 50' toward this monovalent cation site, essentially forming the site. This observation supports a two-step mechanism with ordered substrate binding: ATP first binds to GS, then Glu binds and attacks ATP to form gamma-glutamyl phosphate and ADP, which complete the ammonium binding site. The third substrate, an ammonium ion, then binds to GS, and then loses a proton to form the more active species ammonia, which attacks the gamma-glutamyl phosphate to yield Gln. (5) Because the products (Glu or Gln) of the reactions catalyzed by GS are determined by the molecule (water or ammonium) attacking the intermediate gamma-glutamyl phosphate, this negatively charged ammonium binding pocket has been designed naturally for high affinity of ammonium to GS, permitting glutamine synthesis to proceed in aqueous solution.

Adenosine Diphosphate↗
PubMed1980

The role fo glutamine synthetase and glutamine metabolism in nitrogen metabolite repression, a regulatory phenomenon in the lower eukaryote Neurospora crassa.

Growth of Neurospora crassa on media containing NH4+ leads to the repression of a variety of permeases and alternative pathways which would generate NH4+, so called "ammonium repression." The mutant am2 which lacks NADP-GDH is not subject to ammonium repression of nitrate reductase or urea permease, but like the wild type has repressed levels of these systems when grown in the presence of proline, glutamate or glutamine. The glutamine synthetase (GS) mutant gln-1a has derepressed levels of the aforementioned systems unless grown with glutamine. The oligomeric state of GS depends upon the nitrogen sufficiency of the cell, a tetrameric form predominates under conditions of nitrogen limitation and an octameric form under conditions of nitrogen sufficiency. We have found that the tetrameric form GS predominates in the mutants am2 and gln-1a when they are ammonium derepressed. Th mechanism of NH4+ repression in N. crassa is thought to entail a cessation of positive gene action by the product of the nit-2 regulatory gene. We propose that under conditions of NH4+ sufficiency, and hence glutamine sufficiency, the octameric form of GS represses nit-2 gene expression and thereby achieves ammonium repression.

Enzyme Repression↗
PubMed1995

Glutamine synthetase/glutamate synthase ammonium-assimilating pathway in Schizosaccharomyces pombe.

Kinetic parameters of glutamine synthetase (GS) and glutamate synthase (glutamine-oxoglutarate aminotransferase) (GOGAT) activities, including initial velocity, pH, and temperature optima, as well as Km values, were estimated in Schizosaccharomyces pombe crude cell-free extracts. Five glutamine auxotrophic mutants of S. pombe were isolated following MNNG treatment. These were designated gln1-1,2,3,4,5, and their growth could be repaired only by glutamine. Mutants gln1-1,2,3,4,5 were found to lack GS activity, but retained wild-type levels of NADP-glutamate dehydrogenase (GDH), NAD-GDH, and GOGAT. One further glutamine auxotrophic mutant, gln1-6, was isolated and found to lack both GS and GOGAT but retained wild-type levels of NADP-GDH and NAD-GDH activities. Fortuitously, this isolate was found to harbor an unlinked second mutation (designated gog1-1), which resulted in complete loss of GOGAT activity but retained wild-type GS activity. The growth phenotype of mutant gog1-1 (in the absence of the gln1-6 mutation) was found to be indistinguishable from the wild type on various nitrogen sources, including ammonium as a sole nitrogen source. Double-mutant strains containing gog1-1 and gdh1-1 or gdh2-1 (mutations that result specifically in the abolition of NADP-GDH activity) result in a complete lack of growth on ammonium as sole nitrogen source in contrast to gdh or gog mutants alone.

Glutamate Synthase↗
PubMed1975

Ammonium uptake by nitrogen fixing bacteria I. Azotobacter vinelandii.

Both the changes in the activities of nitrogenase, glutamine synthetase and glutamate dehydrogenase and in the extracellular and intracellular NH4+ concentrations were investigated during the transition from an NH4+ free medium to one containing NH4+ ions for a continuous culture of Azotobacter vinelandii. If added in amounts causing 80-100% repression of nitrogenase, ammonium acetate, lactate and phosphate are absorbed completely, whereas chloride, sulfate and citrate are only taken up to about 80%. After about 1-2 hrs the NH4+ remaining in the medium is absorbed too, indicating the induction or activation of a new NH4+ transport system. One of the new permeases allows the uptake of citrate in the presence of sucrose. Addition of inorganic NH4+ level leads to a reversible rise in the glutamine synthetase activity which is not prevented by chloramphenicol, and to a reversible decrease in nitrogenase activity. During these measurements glutamate dehydrogenase activity remains close to zero. The intracellular NH4+ level of about 0.6 mM does not change when extracellular NH4+ is taken up and repression of nitrogenase starts.

Acetates↗
PubMed2005

Ammonium assimilation in cyanobacteria.

In cyanobacteria, after transport by specific permeases, ammonium is incorporated into carbon skeletons by the sequential action of glutamine synthetase (GS) and glutamate synthase (GOGAT). Two types of GS (GSI and GSIII) and two types of GOGAT (ferredoxin-GOGAT and NADH-GOGAT) have been characterized in cyanobacteria. The carbon skeleton substrate of the GS-GOGAT pathway is 2-oxoglutarate that is synthesized by the isocitrate dehydrogenase (IDH). In order to maintain the C-N balance and the amino acid pools homeostasis, ammonium assimilation is tightly regulated. The key regulatory point is the GS, which is controlled at transcriptional and posttranscriptional levels. The transcription factor NtcA plays a critical role regulating the expression of the GS and the IDH encoding genes. In the unicellular cyanobacterium Synechocystis sp. PCC 6803, NtcA controls also the expression of two small proteins (IF7 and IF17) that inhibit the activity of GS by direct protein-protein interaction. Cyanobacteria perceive nitrogen status by sensing the intracellular concentration of 2-oxoglutarate, a signaling metabolite that is able to modulate allosterically the function of NtcA, in vitro. In vivo, a functional dependence between NtcA and the signal transduction protein PII in controlling NtcA-dependent genes has been also shown.

Amino Acid Sequence↗
PubMed1996

15N-NMR study of ammonium assimilation in Agaricus bisporus.

Ammonium assimilation was studied by feeding [15N]ammonium to actively growing mycelium of Agaricus bisporus. Products of ammonium assimilation were analysed using 15N-NMR. Participation of glutamine synthetase, glutamate synthase and NADP-dependent glutamate dehydrogenase was determined by inhibiting glutamine synthetase with phosphinothricin and glutamate synthase with azaserine. Our results clearly indicate that, under the conditions used, ammonium assimilation is mainly catalysed by the enzymes of the glutamine synthetase/glutamate synthase pathway. No indications were found for participation of NADP-dependent glutamate dehydrogenase. Furthermore, 15N-labelling shows that transamination of glutamate with pyruvate to yield alanine is a major route in nitrogen metabolism. Another major route is the formation of N-acetylglucosamine. Compared to the formation of N-acetylglucosamine there was only a limited formation of arginine.

Agaricus↗
PubMed1976

Control of synbiotic nitrogen fixation in Rhizobia. Regulation of NH4+ assimilation.

This communication is concerned with physiological, biochemical, and genetic studies of the regulation of ammonium (NH4+) assimilation by Rhizobia (root nodule bacteria) that infect leguminous plants. The major conclutions are (i) physiological studies show that Rhizobia are able to assimilate NH4+ for growth only when supplemented with certain organic nitrogen sources (e.g., L-aspartate, L-leucine, L-serine). Addition of as little as 2 mug/ml of L-aspartate supported growth on NH4+ as nitrogen source. In contrast, addition of glutamate in combination with NH4+-blocked NH4+ utilization; (ii) biochemical analysis show that glutamate synthase activity (NADP- and NAD-linked) is always present in cells capable of assimilating NH4+; also cells without glutamate synthase activity were found to be incapable of NH4+ utilization. Glutamate synthase levels were observed to fluctuate markedly depending on the available nitrogen source and on the growth stage of the culture; (iii) mutants were selected in which assimilation of NH4+ is no longer subject to inhibition (repression?) by glutamate. The levels of glutamate synthase activity (NADP-linked) (in the presence of glutamate) show approximately a two-fold increase over the level in the parent strain. The mutants no longer require supplementation with small amounts of organic nitrogen for growth in medium containing inorganic nitrogen (e.g., NH4+ or NO3-); (iv) these findings are discussed in relation to the working model of symbiotic nitrogen fixation recently proposed (O'Gara and Shanmugam (1976), Biochim. Biophys. Acta 437, 313--321).

Aspartic Acid↗
PubMed2005

Optimizing experimental design to estimate ammonia and nitrite oxidation biokinetic parameters from batch respirograms.

Knowledge of relative NH(4+)-N to NO(2-)-N oxidation and NO(2-)-N to NO(3-)-N oxidation dynamics is essential before application of either single-step or two-step nitrification models to fit batch nitrification respirograms. We have previously shown that two step nitrification models based on respirometry permit the estimation of kinetic parameters for both nitrification steps from a single respirogram associated with NH(4+)-N to NO(3-)-N oxidation. However, two-step model parameter estimates are meaningful only under circumstances when the respirograms contain sufficient kinetic information pertaining to both steps. In this study, we present an operationally amenable extant batch nitrification respirometric assay to engender maximal information content in the resulting respirograms with respect to both constituent nitrification steps. The developed design consists of an initial NH(4+)-N pulse to a nitrifying biomass sample followed by an additional NO(2-)-N pulse at an optimal time point, which can be rigorously determined by maximizing the value of the determinant of the Fisher information matrix, Det(F) or, alternatively, by visually identifying the point of NH(4+)-N depletion during the respirometric assay. The proposed design is applicable for accurate determination of the Monod kinetic parameter estimates for both nitrification steps from batch respirograms even when the pseudo-first order rate coefficients for the two nitrification steps are nearly equal; a condition under which standard NH(4+)-N to NO(3-)-N respirograms typically lack information with respect to NO(2-)-N oxidation.

Ammonia↗
PubMed2006

Nitrous oxide emissions from secondary activated sludge in nitrifying conditions of urban wastewater treatment plants: effect of oxygenation level.

In order to better understand the mechanisms of N(2)O emissions from nitrifying activated sludge of urban WWTPs, sludge from the Valenton plant (Paris conurbation) are subjected to lab-scale batch experiments under various conditions of oxygenation. The results show that the highest N(2)O emissions (7.1 microgN-N(2)OgSS(-1) h(-1) in average) occur at a dissolved oxygen (DO) concentration of around 1mgO(2)L(-1). These high emissions at low oxygenation (from 0.1 to 2 mg O(2)L(-1)) are due to two processes: autotrophic nitrifier denitrification and heterotrophic denitrification. Nitrifier denitrification always dominates, representing from 58% to 83% of the N(2)O production. This N(2)O production originating from nitrifying activated sludge becomes 8 times higher when nitrite is added at a DO of 1 mg O(2)L(-1); a decrease is observed both at higher and lower oxygenation. Heterotrophic denitrification represents less than 50% of the N(2)O production, decreasing from 42% to 17% when oxygenation increases from 0.1 to 2 mg O(2) L(-1). We show that ammonium oxidizing bacteria (AOB) can shift to nitrifier denitrification when oxygen is depleted in the environments including in the WWTPs, nitrite then plays the role of oxygen as the final electron acceptor. As opposed to what happens in nitrification, the end products of nitrifier denitrification are gaseous forms of nitrogen, where N(2)O is not negligible compared to N(2). Overall, N(2)O emissions represent 0.1-0.4% of oxidized NH(4)(+), depending on the oxygenation level. N(2)O emissions would range from 0.11 to 0.42 TN-N(2)O day(-1) for a tertiary treatment of the Paris wastewater effluents, consisting exclusively of activated sludge nitrification.

Ammonia↗
PubMed2001

An anxiolytic agent, dihydrohonokiol-B, inhibits ammonia-induced increases in the intracellular Cl(-) of cultured rat hippocampal neurons via GABA(c) receptors.

The effects of an anxiolytic honokiol derivative, dihydrohonokiol-B (DHH-B) [3'-(2-propenyl)-5-propyl-(1,1'-biphenyl)-2,4'-diaol], on ammonia-induced increases in the intracellular Cl(-) concentration ([Cl(-)](i)) were examined using primary cultured rat hippocampal neurons. DHH-B (1-100 ng/ml), but not an inactive isomer of honokiol, magnolol (100 ng/ml), dose-dependently inhibited the ammonia-induced increases in [Cl(-)](i) without any changes in the control [Cl(-)](i). Such an effect of DHH-B was blocked by a gamma-aminobutylic acid A (GABA(A)) and GABA(C) Cl(-) channel blocker, 100 microM picrotoxin, and a GABA(C) receptor blocker, 10 microM (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid, but not by a GABA(A) receptor blocker, 10 microM bicuculline. Further, a GABA(C) receptor agonist, 200 microM cis-4-aminocrotonic acid, but not a GABA(A) receptor agonist, 10 microM muscimol, mimicked the effect of DHH-B. Thus, DHH-B appears to protect neurons from the ammonia-induced increases in [Cl(-)](i) through GABA(C) receptor stimulation.

Ammonia↗
PubMedDate not supplied

Cyanobacteria-eukaryotic plant symbioses.

N2-fixing heterocystous cyanobacteria develop in symbiotic association with a small number of eukaryotic plant species belonging to the algae, fungi, liverworts, ferns, gymnosperms and angiosperm. When the free-living cyanobacteria develop in symbiosis, they become modified morphologically, physiologically and biochemically. The symbiosis are relatively specific, and among the changes which occur in the endophytic cyanobacteria are increases in the size of the vegetative cells, changes in the ultrastructure of the vegetative cells, a tendency for a reduction in the filamentous habit, an increased heterocyst frequency when another photosynthetic partner is present, reduced activities of glutamine synthetase and glutamate synthase, and NH4+ release by; the endophytic cyanobacteria. These and other aspects are considered, emphasizing, in particular, work carried out in the authors' laboratory.

Cyanobacteria↗
PubMed2001

Ammonia exchange between the atmosphere and the surface waters at two locations in the Chesapeake Bay.

Excess phytoplankton production, which contributes to hypoxic conditions, is nitrogen limited in the Chesapeake Bay during the summer months. Therefore, understanding the flux of ammonia by direct deposition to the biologically active surface layer is critical to understanding the nutrient dynamics of the bay. This paper presents the results of a 2-yr study measuring gaseous ammonia (NH3) and aerosol ammonium (NH4+) in Baltimore and Solomons, MD, from which direct atmospheric loading of total ammonia (Nt = NH3 + NH4+) to the Chesapeake Bay is estimated. Mean atmospheric concentrations of total ammonia for Baltimore and Solomons were 2.7 +/- 1.7 and 1.0 +/- 0.8 microg of N m(-3), respectively. Monte Carlo estimates of gross dry deposition ranged from <100 to 4900 microg of N m(-2) d(-1). However, based upon water quality parameters, Monte Carlo estimates of gross volatilization of NH3 were calculated to range from <100 to 7700 microg of N m(-2) d(-1). The resulting net air-sea exchange flux varied seasonally from a net deposition into the water during the winter to a net volatilizing into the atmosphere during the summer. A total of 60% of the paired air-water samples had flux estimates that were not significantly different than equilibrium at the 90% confidence interval. The gross deposition, gross volatilization, and net air-sea fluxes were greater and more variable in Baltimore relative to the rural site. Atmospheric ammonia concentrations decrease during the winter at the rural site. However, the net exchange is still into the water due to an exponential decrease in [NH3]eq with temperature. These results indicate that the nitrogen-limited Chesapeake Bay can act as a source of ammonia to the local atmosphere.

Air Pollutants↗