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PubMed1987

Steady-state kinetic analysis for the reaction of ammonium and alkylammonium ions with methylamine dehydrogenase from bacterium W3A1.

The steady-state kinetic mechanism for the reaction of n-alkylamines and phenazine ethosulfate (PES) or phenazine methosulfate (PMS) with methylamine dehydrogenase from bacterium W3A1 is found to be of the ping-pong type. This conclusion is based on the observations that 1/v versus 1/[methylamine] or 1/[butylamine] plots, at various constant concentrations of an oxidizing substrate, and 1/v versus 1/[PES] or 1/[PMS] plots, at various constant concentrations of a reducing substrate, are parallel. Additionally, the values of kcat/Km for four n-alkylamines are identical when PES is the oxidizing substrate, as were the kcat/Km values for four reoxidizing substrates when methylamine was the reducing substrate. Last, analysis of steady-state kinetic data obtained when methylamine and propylamine are presented to the enzyme simultaneously and PES and PMS are used simultaneously also supports the involvement of a ping-pong mechanism. The enzymic reaction with either methylamine or PES is dependent on the ionic strength, and the data indicate that each interacts with an anionic site on methylamine dehydrogenase. The presence of ammonium ion at low concentration activates the enzyme, but at high concentration this ion is a competitive inhibitor in the reaction involving methylamine and the enzyme. A complete steady-state mechanism describing these ammonia effects is presented and is discussed in light of the nature of the pyrroloquinoline quinone cofactor covalently bound to the enzyme.

Amines↗
PubMed2000

Leaf-specific overexpression of plastidic glutamine synthetase stimulates the growth of transgenic tobacco seedlings.

The impact of increased plastidic glutamine synthetase (GS-2; EC 6.1. 3.2) activity on foliar amino-acid levels and on biomass production was examined in transgenic tobacco. For that, tobacco was transformed via Agrobacterium tumefaciens with a binary vector containing a tobacco GS-2 cDNA downstream of the leaf-specific soybean ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit gene promotor. Two transgenic tobacco lines with 15- to 18-fold higher foliar GS-2 transcript levels than the wild type were obtained. The GS-2 protein pools and the specific GS-2 activities were, however, only 2- to 2.3-fold higher in the leaves of the transgenic plants than in the leaves of the wild type. This discrepancy may reflect a post-transcriptional control of GS-2 protein accumulation. The increased GS-2 activity was correlated with a decrease in the leaf ammonium pool (3.7-fold) and an increase in the levels of some free amino acids, including glutamate (2. 5-fold) and glutamine (2.3-fold). The accumulation of soluble protein per unit fresh weight, however, remained unchanged. This result indicates that a process downstream of the synthesis of the primary organic products of N-assimilation is limiting leaf protein accumulation. Nevertheless, the overexpression of GS-2 stimulated the growth rate of the transgenic tobacco seedlings which, consequently, were larger (20-30% on a fresh-weight basis) than wild-type seedlings grown under identical conditions. This result suggests that GS-2 is the rate-limiting enzyme during biomass production in tobacco seedlings. The requirement for glutamate as the ammonium acceptor in the reaction catalysed by GS-2 may imply that there is co-regulation of GS-2 and ferredoxin dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) gene expression. Increased leaf GS-2 activity had, however, no influence on the foliar Fd-GOGAT protein abundance. This result suggests that in tobacco leaves, more Fd-GOGAT is present than required to meet the demands of primary ammonium assimilation and that there is no strong interdependence between GS-2 and Fd-GOGAT protein expression.

Amino Acid Oxidoreductases↗
PubMed2001

Neurotensin-and EGF-induced metabolic activation of colon carcinoma cells is diminished by dietary flavonoid cyanidin but not by its glycosides.

Dietary polyphenols, including anthocyanidins and their glycosides anthocyanins, are suggested to be involved in the protective effects of fruits and vegetables against cancer. Very few data are available concerning the effects of anthocyanidins/anthocyanins on cellular processes induced by growth factors such as neurotensin and epidermal growth factor (EGF), which are implicated in the pathophysiology of colon cancer. Here, we show that neurotensin and EGF caused an increase in the extracellular acidification rate, which could reflect the activity of cellular metabolism, in the human carcinoma cell line HT29 clone 19A. Neurotensin and EGF also caused a strong rise in the intracellular Ca2+ concentration, induced phosphorylation of extracellular signal-regulated kinases (ERK1 and ERK2), and stimulated growth of human carcinoma cells. Cyanidin (10 microM), but not its glycosides cyanin and idaein, was able to inhibit the neurotensin- and EGF-induced increased rate of extracellular acidification. In contrast to N-ethyl-N-isopropyl amiloride, an inhibitor of Na+/H+ exchange, cyanidin did not alter the rate of intracellular pH recovery of cells loaded by NH3/NH4+, indicating that cyanidin inhibits cellular metabolism, rather than directly altering Na+/H+ exchange. Cyanidin, but not cyanin and idaein, was able to inhibit an increase in intracellular Ca2+ concentration induced by neurotensin. Neurotensin- and EGF-induced phosphorylation of ERKs was not affected by cyanidin, cyanin, and idaein at < or = 100 microM. Only cyanidin (100 microM), but not cyanin and idaein, was able to inhibit cellular growth induced by EGF. Thus these findings suggest that a dietary polyphenol cyanidin, but not its glycosides, is a potent inhibitor of mitogen-induced metabolic activity, increase in free intracellular Ca2+, and cellular growth of cultured colon carcinoma cells.

Ammonia↗
PubMed1992

Arginine catabolism in the phototrophic bacterium Rhodobacter capsulatus E1F1. Purification and properties of arginase.

The phototrophic bacterium Rhodobacter capsulatus E1F1 grew with L-arginine or L-homoarginine as nitrogen source under light/anaerobiosis. However, when L-arginine was used as the only source of both carbon and nitrogen, the bacterium exhibited weak growth levels and the excess of nitrogen was excreted to the medium as ammonia. By contrast, L-ornithine was used under phototrophic conditions as either nitrogen or carbon source. Other compounds of the arginine catabolic pathways, such as putrescine or proline, also supported phototrophic growth of this bacterium. Under heterotrophic/dark conditions, R. capsulatus always showed a low growth rate with those nitrogen compounds. Cells growing on media containing L-arginine, L-homoarginine or L-ornithine induced an Mn(2+)-dependent arginase activity regardless of the presence of ammonium ions and other readily utilizable nitrogen sources. Arginase activity was strongly inhibited by Zn2+, Cu2+, borate, L-cysteine, L-ornithine and gamma-guanidinobutyrate. Mercurials also inactivated arginase, the activity being partially restored by the presence of thiols. Arginase was purified to electrophoretic homogeneity and found to consist of four identical subunits of 31 kDa. The molecular parameters and kinetic constants of arginase from R. capsulatus E1F1 resembled those previously described for the Saccharomyces cerevisiae enzyme rather than those of bacterial arginases.

Arginase↗
PubMed1976

Equilibration of 15N-labeled amino compounds in man.

Following an overnight fast, either 15N-labeled glycine, or ammonium chloride, or L-aspartate was orally administered to human volunteers in equal hourly aliquots for 8-12 h. In a parallel series of experiments, [15N]glycine and [15N]ammonium chloride were given intravenously at a constant rate for 10-12 h. The amount of 15N given ranged between 2.7 and 27.3 mg/h. Five hundred milligrams of sodium benzoate were given hourly. Venous blood and urine samples were collected serially. The 15N enrichment of the plasma amino nitrogen, urinary ammonia, hippuric acid, and urea were determined. Irrespective of the 15N carrier used or the route of administration, the plasma amino nitrogen, urinary ammonia, and hippuric acid 15N enrichments approached a plateau within 6-10 h. We concluded that human [15N]glycine metabolism was not atypical of amino acids and that mixing, rather than nitrogen interchange reactions, determines the rate in attaining an approximate plateau.

Amino Acids↗
PubMed1989

Nitrilase of Rhodococcus rhodochrous J1. Purification and characterization.

Nitrilase was purified from an extract of isovaleronitrile-induced cells of Rhodococcus rhodochrous J1 in seven steps. In the last step, the enzyme was crystallized by adding ammonium sulfate. The crystallized enzyme appeared to be homogeneous by polyacrylamide electrophoresis, ampholyte electrofocusing and double immunodiffusion in agarose. The enzyme has a molecular mass of about 78 kDa and consists of two subunits identical in molecular mass. The purified enzyme exhibits a pH optimum of 7.6 and a temperature optimum of 45 degrees C. The enzyme catalyzed stoichiometrically the hydrolysis of benzonitrile to benzoic acid and ammonia, and no formation of amide was detected. The enzyme required thiol compounds such as dithiothreitol, L-cysteine or reduced glutathione to exhibit maximum activity. The enzyme was specific for nitrile groups attached to an aromatic or heteroaromatic ring, e.g. benzonitrile, 3-chlorobenzonitrile, 4-tolunitrile, 2-furonitrile and 2-thiophenecarbonitrile. The comparison of the properties of the enzyme with other nitrilases and nitrile hydratases has been also discussed.

Amino Acids↗
PubMed2003

ATO3 encoding a putative outward ammonium transporter is an RTG-independent retrograde responsive gene regulated by GCN4 and the Ssy1-Ptr3-Ssy5 amino acid sensor system.

Respiratory deficient yeast cells such as rhoo petites activate an inter-organelle signaling pathway called retrograde regulation. This results in changes in the expression of a subset of nuclear genes leading to major reconfigurations of metabolism that enable cells to adapt to the respiratory deficient state. Previous studies have focused on the role of three positive regulatory factors in the retrograde pathway, Rtg1p, Rtg2p, and Rtg3p, which are essential for both basal and elevated expressions of some, but not all, retrograde responsive genes. Here we characterize the retrograde regulation of one of those genes, ATO3, whose elevated expression in rhoo petites is largely independent of RTG gene function. ATO3 encodes a member of the YaaH family of proteins that is a putative outward ammonium transporter. We show that Ato3p-green fluorescent protein is preferentially localized to the plasma membrane of mother cells. rhoo petites express more Ato3p-green fluorescent protein in their plasma membrane than do rho+ cells, consistent with the elevated level of ATO3 transcripts in rhoo cells. We find that ATO3 expression has two levels of control, both of which are connected to amino acid sensing and regulation. The first involves GCN4, which is required for the bulk of ATO3 expression. The second involves the Ssy1-Ptr3-Ssy5 amino acid sensor system, which is preferentially required for elevated ATO3 expression in rhoo cells. We propose that ATO3 is induced in rhoo cells to eliminate the excess ammonia that arises because of a potential defect in ammonia assimilation in those cells.

Amino Acids↗
PubMed1979

Determination of 15N-ammonia by chemical ionization mass spectrometry.

The tracing of ammonium nitrogen is important in hepatic diseases, especially in liver cirrhosis with hyperammonemia. In this paper, a new convenient method is described for determining stable isotope 15N-labeled ammonia using the Conway apparatus and chemical ionization mass spectrometry. The minimum quantity of ammonia necessary for reliable measure of 15N content was 0.1 muMol. The average error was 5.3%. In clinical application, 4 ml of blood after oral administration of 1 g of 15NH4Cl was sufficient for measurement.

Humans↗
PubMed1978

Regulatory properties of the nitrogenase from Rhodopseudomonas palustris.

Ammonium salts, glutamine, asparagine, and urea cause an immediate inactivation (switch-off) of light-dependent acetylene reduction in intact cells of the photosynthetic bacterium Rhodopseudomonas palustris. This effect is reversible showing the same kinetic pattern of inactivation and reactivation with all effector compounds. Its duration depends on the amount of effector added to the cells. Both nitrogenase components are found catalytically active in a cell-free preparation after enzyme switch-off in vivo. Involvement of the ammonia assimilating system in this regulatory mechanism is indicated by the following observations: ammonia uptake during the switch-off period, resumption of acetylene reduction after disappearance of ammonia from the outer medium, and persistence of enzyme switch-off with dihydrogen and thiosulfate as electron donors in the absence of an additional carbon source. Nitrogenase activity in crude extracts is non-linear with time and is stimulated by manganese ions. After resolution of nitrogenase into its MoFe--protein and Fe--protein these properties are lost, indicating the presence of an activating factor. Nitrogenase of R. palustris cross reacts reciprocally with the complementary proteins of Azotobacter vinelandii, but not with those of Clostridium pasteurianum.

Acetylene↗
PubMed1996

Deposition of nitrogen-containing compounds to an extensively managed grassland in central Switzerland.

During four intensive observation periods in 1992 and 1993, dry deposition of nitrogen dioxide (NO(2)) and ammonia (NH(3)), and wet deposition of nitrogen (N) were determined. The measurements were carried out in a small, extensively managed litter meadow surrounded by intensively managed agricultural land. Dry deposition of NH(3) was estimated by the gradient method, whereas eddy correlation was used for NO(2). Rates of dry deposition of total nitrate (= nitric acid (HNO(3)) + nitrate (NO(3)(-))), total nitrite (= nitrous acid (HONO) + nitrite (NO(2)(-))) and aerosol-bound ammonium (NH(4)(+)) were estimated using deposition velocities from the literature and measured concentrations. Both wet N deposition and the vertical NH(3) gradient were measured on a weekly basis during one year. Dry deposition was between 15 and 25 kg N ha(-1) y(-1), and net wet deposition was about 9.0 kg N ha(-1) y(-1). Daily average NO(2) deposition velocity varied from 0.11 to 0.24 cm s(-1). Deposition velocity of NH(3), was between 0.13 and 1.4 cm s(-1), and a compensation point between 3 and 6 ppbV NH(3) (ppb = 10(-9)) was found. Between 60 and 70% of dry deposition originated from NH(3) emitted by farms in the neighbourhood. It is concluded that total N deposition is exceeding the critical load for litter meadows, is highly correlated to local NH(3) emissions, and that NH(3) is of utmost importance with respect to possible strategies to reduce N deposition in rural regions.

Journal Article↗
PubMed2006

Structural and functional insights into the AmtB/Mep/Rh protein family.

X-ray crystallography revealed a similar architecture of the ammonium transport protein AmtB from Escherichia coli and the homologous protein Amt-1 from Archaeoglobus fulgidus. Furthermore, the atomic structures suggest that the proteins conduct ammonia (NH3) rather than ammonium ions (NH4+). These findings indicate that the more than 350 members of the ammonium transporter/methylamine permease/Rhesus (Amt/Mep/Rh) protein family found in archaea, bacteria, fungi, plants and animals are ammonia-conducting channels rather than ammonium ion transporters. The essential part of these proteins is the narrow hydrophobic ammonia-conducting pore with two highly conserved histidine residues located in the middle of the pore. A specific ammonium ion binding site is found at the extracellular entry site of E. coli AmtB. E. coli AmtB and its regulator GlnK form an effective ammonium sensory system that couples intracellular gene regulation by the nitrogen control system to external changes in ammonium availability. Based on structural and functional analysis of various mutants, two conserved histidine residues were found to be essential for substrate conductance also in the functional eukaryotic ammonium transporters. The next big challenge in the field surely is to determine the atomic structure of Rh proteins.

Ammonia↗
PubMed2002

Alteration of amino acid metabolism in neuronal aggregate cultures exposed to hypoglycaemic conditions.

The neuronal effects of glucose deficiency on amino acid metabolism was studied on three-dimensional cultures of rat telencephalon neurones. Transient (6 h) exposure of differentiated cultures to low glucose (0.25 mm instead of 25 mm) caused irreversible damage, as judged by the marked decrease in the activities of two neurone-specific enzymes and lactate dehydrogenase, 1 week after the hypoglycemic insult. Quantification of amino acids and ammonia in the culture media supernatants indicated increased amino acid utilization and ammonia production during glucose-deficiency. Measurement of intracellular amino acids showed decreased levels of alanine, glutamine, glutamate and GABA, while aspartate was increased. Added lactate (11 mm) during glucose deficiency largely prevented the changes in amino acid metabolism and ammonia production, and attenuated irreversible damage. Higher media levels of glutamine (4 mm instead of 0.25 mm) during glucose deprivation prevented the decrease of intracellular glutamate and GABA, while it further increased intracellular aspartate, ammonia production and neuronal damage. Both lactate and glutamine were readily oxidized in these neuronal cultures. The present results suggest that in neurones, glucose deficiency enhances amino acid deamination at the expense of transamination reactions. This results in increased ammonia production and neuronal damage.

Amino Acids↗
PubMed2001

Distribution of ammonium-N in the water-soil interface of a surface-flow constructed wetland for swine wastewater treatment.

Most livestock wastewaters treated in constructed wetlands are typically rich in ammonium N. The objective of this study was to evaluate the soil-water ammonium distribution and the diffusive flux through the soil-water interface. Wetland system 1 (WS1) was planted to rush and bulrushes, and wetland system 2 (WS2) was planted to bur-reed and cattails. Nitrogen was applied at a rate of 2.5 g m(-2) d(-1). Interstitial soil water was sampled at 9, 24, 50, and 70 m from the inlet. In both wetlands, we found that NH4+ diffusion gradient and N losses were highest in the wetland system with lowest water depth. From other studies, we knew that shallower depths may have promoted a more effective interfacing of nitrifying and denitrifying environments. In turn, this N reduction in the water column may be the reason for steady NH4+-N upward diffusion fluxes. The assumed mechanism for N removal has been nitrification and denitrification but ammonia volatilization could also have occurred. Although diffusion may explain a significant portion of the material transport between the soil-water interface, the large differences in concentrations between outlet and inlet need further explanation.

Agriculture↗
PubMed2004

Nutrient removal from shrimp farm effluent by aquatic plants.

Duckweed was used to treat effluent from a shrimp farm in a batch wise and recirculation system. The result showed that duckweed could efficiently remove nutrients in the effluent, especially ammonia, which seemed to be the preferred nitrogen source of the plant. Red tilapia was used in the recirculation system and showed high potential in removal of uneaten shrimp feed.

Animals↗
PubMed2006

Ammonia affects the activity and expression of soluble and particulate GC in cultured rat astrocytes.

Neurotoxic effects of ammonia are mediated by increased accumulation of nitric oxide (NO), which combines with free radicals to form a highly toxic compound, peroxynitrite. Previous experiments in vivo and in vitro have suggested that this phenomenon engages neuron-derived NO and is coupled to changes in the accumulation of cGMP. The present study accounted for the facts that: (i) astrocytes, not neurons are the morphological target of ammonia, and (ii) both NO-dependent, soluble (sGC) and NO-independent, particulate guanylate cyclase (pGC) mediate cGMP production in the cells. Neocortical rat astrocytes were treated for 1 or 24 h with 5 mM ammonium chloride ("ammonia") and then subjected to: (i) cGMP measurement, and (ii) mRNA and/or protein expression analysis of alpha1 and beta1 subunits of sGC and two pGC forms: pGC-A and pGC-B. Treatment with ammonia for 1h increased accumulation of cGMP and sGCbeta1 mRNA expression, without producing significant changes in the protein expression. This was followed by a decrease of cGMP level at 24 h treatment, associated with a decreased expression of sGCbeta1 and sGCalpha1 mRNA and sGCbeta1 protein. Expression of pGC-A and pGC-B mRNA was elevated in ammonia-treated astrocytes after 24 h. Accordingly, increased cGMP accumulation was noted in the presence of a specific sGC inhibitor (ODQ). The results show that ammonia affects cGMP production in astrocytes, and that this may involve not only sGC but also pGC.

Acute Disease↗
PubMed1999

Determination of nivalenol and deoxynivalenol in wheat using liquid chromatography-mass spectrometry with negative ion atmospheric pressure chemical ionisation.

A new, rapid and sensitive method has been developed for the determination of nivalenol (NIV) and deoxynivalenol (DON) by using HPLC in combination with an atmospheric pressure chemical ionization (APCI)-interface and a single quadrupole mass spectrometer. Different LC and MS parameters have been optimized prior to this in order to obtain better results and sensitivity. The effect of nebulizing temperature on the sensitivity and fragmentation of NIV and DON in an APCI interface was investigated. Also, the influence of the cone voltage on the fragmentation pattern was studied, which was shown to have a tremendous effect. Furthermore, the effect of modifiers such as ammonium acetate, acetic acid and ammonia on the ionisation yield of the above substances have been investigated. The extraction was carried out using acetonitrile-water. A two step purification was then applied on two different Mycosep clean up columns. We have used a modified, rapid and isocratic HPLC method combined with a negative ion APCI-MS for the separation and quantitative determination of NIV and DON in wheat extract. An RP C18 column was used for the separation of selected compounds in wheat extract with water-acetonitrile-methanol (82:9:9, v/v/v) at a flow-rate of 1 ml/min without a split. Calibration curves show good linearity and reproducibility. The detection limit and precision were determined for NIV and DON. Both compounds could be detected down to microg/kg level in wheat using selected ion monitoring of the [M-H]- ions and the main fragments.

Atmospheric Pressure↗
PubMed1971

Physiological studies of methane and methanol-oxidizing bacteria: oxidation of C-1 compounds by Methylococcus capsulatus.

Methylococcus capsulatus grows only on methane or methanol as its sole source of carbon and energy. Some amino acids serve as nitrogen sources and are converted to keto acids which accumulate in the culture medium. Cell suspensions oxidize methane, methanol, formaldehyde, and formate to carbon dioxide. Other primary alcohols are oxidized only to the corresponding aldehydes. Oxidation of formate by cell suspensions is more sensitive to inhibition by cyanide than is the oxidation of other one carbon compounds. This is due to the cyanide sensitivity of a soluble nicotinamide adenine dinucleotide-specific formate dehydrogenase. Oxidation of formaldehyde and methanol is catalyzed by a nonspecific primary alcohol dehydrogenase which is activated by ammonium ions and is independent of pyridine nucleotides. Some comparisons are made with a strain of Pseudomonas methanica.

Alcohol Oxidoreductases↗
PubMed2001

Decomposition of alkyl-substituted urea molecules at a hydroxide-bridged dinickel center.

The interactions between N-methylurea, N,N'-dimethylurea, N,N-dimethylurea, tetramethylurea, and thiourea and the hydroxide-bridged dinickel complex [Ni(2)(mu-OH)(mu-H2O)(bdptz)(H2O2](OTs)(3) were investigated. Structural characterization of [Ni(2)(mu-OH)(mu-H2O)(bdptz)(Me-urea)(CH3CN)](ClO4)(3) (1) and [Ni(2)(mu-OH)(mu-H2O)(bdptz)(thiourea)(CH3CN)](ClO4)(3) (2) provided insight into the interactions of the substrates with the dinickel center. In 1, the methylurea molecule coordinates to the dinickel complex through its carbonyl oxygen atom. Complex 2 has a similar geometry, with the thiourea molecule bound to a nickel ion through its sulfur atom. When the urea substrates are heated in the presence of the hydroxide-bridged dinickel complex, N-methylurea and N,N-dimethylurea react to form methylammonium cyanate and dimethylammonium cyanate, respectively. After long reaction times, thiourea reacts similarly, producing ammonium thiocyanate. The other substrates are unreactive. These results indicate that the dinickel complex promotes the elimination of alkylamines from urea substrates to form cyanate but cannot effect the direct hydrolysis of such substrates.

Alkanes↗