Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “AMMONIA”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed2001

Comparative phylogeny of the ammonia monooxygenase subunit A and 16S rRNA genes of ammonia-oxidizing bacteria.

A fragment of the ammonia monooxygenase gene (amoA) from 31 strains of ammonia-oxidizing bacteria (AOB) was sequenced and analysed phylogenetically. The results were compared with the phylogeny of 16S rDNA from AOB. For most groups of AOB we found a high consistency between the phylogenetic trees based on the 16S rDNA and amoA sequences. Although it is not a phylogenetic marker, using the amoA as a probe when studying microbial diversity will probably reduce the amount of non-AOB detected, compared to using rDNA based probes. The data presented in this paper extend and improve the basis for application of amoA in studies of AOB in the environment.

Genes, Bacterial↗
PubMed1981

Regulation of ammonia assimilation in ammonia-limited chemostat cultures of Escherichia coli ML 30: evidence of bistability.

In a preceding paper evidence of two stationary stable states (bistability) in the specific activity of glutamine synthetase (GS) in ammonia-limited steady-state cultures of Escherichia coli ML 30 at dilution rates (D) about 0.15 h-1 was described (Müller et al. 1977). For better understanding of the regulation mechanisms leading to GS bistability chemostat experiments were performed over a wide range of dilution rates up to D = 0.8 h-1. For each steady state the specific activities of GS and glutamate dehydrogenase (GDH)--the other key enzyme of the two NH3 assimilation routes in E. coli--and in addition the remaining NH3 concentration in the culture liquid were determined. Parallel to GS bistability two states of GDH activity and NH3 concentration are found. The higher state of GS is connected with a lower GDH activity and NH3 concentration. With rising D the GS activities decrease whereas GDH activities and NH3 concentrations increase. Since no adenylation of the GS is detectable GS bistability seems to be regulated on the level of enzyme synthesis like GDH bistability. From the experimental findings a mathematical model is derived based on the bottle neck enzyme theory of growth. It describes the dependence between the specific growth rates on the one hand and the specific enzyme activities and NH3 concentration on the other. It is shown that the specific uptake rate of the limiting NH3 and the specific growth rates, respectively, depend on the simultaneous action of two bottle neck enzymes which are connected by a regulative link.

Ammonia↗
PubMed1985

The apparent Km of ammonia for carbamoyl phosphate synthetase (ammonia) in situ.

Experiments with carbamoyl phosphate synthetase (ammonia) in solution and in isolated mitochondria are reported which show the following. NH3 rather than NH4+ is the substrate of the enzyme. The apparent Km of NH3 for the purified enzyme is about 38 microM. The apparent Km for NH3 measured in intact isolated mitochondria is about 13 microM. This value was obtained for both coupled and uncoupled mitochondria and was unchanged when the rate of carbamoyl phosphate synthesis was increased 2-fold by incubating uncoupled mitochondria in the presence of 5 mM-N-acetylglutamate. According to the literature, the concentration of NH3 in liver is well below the measured apparent Km. On the basis of this and previous work we conclude that, quantitatively, changes in liver [NH3] and [ornithine] are likely to be the most important factors in the fast regulation of synthesis of carbamoyl phosphate and urea. This conclusion is consistent with all available evidence obtained with isolated mitochondria, isolated hepatocytes, perfused liver and whole animals.

Ammonia↗
PubMed1995

Irritant and protective action of urea-urease ammonia in rat gastric mucosa. Different effects of ammonia and ammonium ion.

The effects of urea-urease-ammonia on the rat gastric mucosa were examined and compared with those of NH4OH and NH4Cl. The mucosal application of urea with urease produced a reduction in potential difference (PD) in a dose-related manner for urea, and a significant drop was observed by > 0.1% urea in the presence of 100 units urease. Such PD reduction was also observed when the mucosa was exposed to either NH4OH (> 0.03%) or NH4Cl (> 1%); delta PD (20 mV) caused by 0.3% NH4OH and 3% NH4Cl was equivalent to that induced by 0.5% urea+urease (100 units). The combined oral administration of urea (approximately 6%) and urease (100 units) did not induce any macroscopic damage in the gastric mucosa. NH4Cl given orally had no or little effect on the mucosa at any dose levels even at 10%, while NH4OH given orally caused hemorrhagic lesions in the mucosa at the dose of > 0.3%. In contrast, both urea+urease and NH4Cl given prior to HCl/ethanol protected the gastric mucosa against damage in a dose-related manner, and a significant effect was obtained by urea at > 0.5% and by NH4Cl at > 1%. NH4OH was also effective in reducing the severity of HCl/ethanol-induced gastric lesions at lower dose (0.3%). The protective effect of urea+urease was attenuated significantly by prior administration of indomethacin or coadministration of hydroxyurea, while that of NH4Cl or NH4OH was mitigated by indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed2003

Use of the ammonia-oxidizing bacterial-specific phylogenetic probe Nso1225 as a primer for fingerprint analysis of ammonia-oxidizer communities.

Autotrophic ammonia-oxidizing bacteria (AOB) are an essential component of nitrifying wastewater treatment systems. The molecular tools used in group-specific studies are mostly based on the sequence of the 16S rRNA gene, but they have not proved to be fully specific. In this study, the sequence of the FISH probe Nso1225R was used as a reverse primer in order to analyze the AOB composition of several environmental samples by denaturing gradient gel electrophoresis (DGGE). For this purpose, samples from several environments, including aerated reactors, water treatment wetlands, and pilot plants, both aerobic and anaerobic, were analyzed. PCR fragments displayed a DGGE pattern consisting of bands melting between 30 and 40% denaturant, and a series of unresolved bands above 45%, mostly corresponding to AOB and beta-non-AOB, respectively. This second set of bands corresponded to environments subjected to severe oxygen restrictions. AOB sequences showed similarity percentages higher than 92% with those of known beta-AOB. Nso1225R, therefore, proved to be a good molecular phylogenetic marker for AOB samples from well-aerated systems, showing a higher specificity than the group-specific primers used previously.

Ammonia↗
PubMed1991

L-carnitine protection in ammonia intoxication. Effect of aminocarnitine on carnitine-dependent metabolism and acute ammonia toxicity.

Intraperitoneal administration of L-carnitine (16 mmol/kg) was reported by O'Connor et al. (FEBS Lett 166: 331-334, 1984) to fully protect mice from ammonium acetate given at a dose that kills 100% of untreated controls. Other investigators either have failed to observe protection by L-carnitine or have attributed the increased survival to a nonspecific "osmoprotective effect" of quaternary ammonium compounds. In the present studies we have confirmed the protective effect of L-carnitine in acute ammonia intoxication and have shown that D-carnitine and deoxycarnitine, close structural analogs of L-carnitine, are without protective effect. Although D-carnitine and deoxycarnitine do not support L-carnitine-dependent metabolisms, they are transported into tissues and their solutions are osmotically identical to those of L-carnitine; lack of protection by D-carnitine and deoxycarnitine suggests that metabolic rather than nonspecific osmotic effects account for L-carnitine-mediated protection. Further supporting the importance of L-carnitine-dependent metabolisms, we found that mice exhibited increased sensitivity to ammonium acetate when pretreated with DL-aminocarnitine, acetyl-DL-aminocarnitine or palmitoyl-DL-aminocarnitine, potent inhibitors of the carnitine acyltransferases. Interestingly, intraperitoneal injection of hyperosmotic solutions of sodium chloride or sucrose did afford significant protection against subsequently administered ammonium acetate. This phenomenon, which may be due to interference with ammonium acetate uptake from the peritoneal cavity or to reduction of cerebral edema by increased plasma osmolarity, apparently does not play a major role in L-carnitine-mediated protection since, as noted, hyperosmotic D-carnitine and deoxycarnitine solutions were not protective.

Acetates↗
PubMed1985

An improved method of ammonia determination, applicable to amidases and other ammonia-producing enzyme systems of mycobacteria.

The colorimetric estimation of amidase activity, using both qualitative and quantitative determinations of ammonia, is widely used for the differentiation of mycobacteria. At present the generally used phenol-hypochlorite method requires heating of the test solution to 90 degrees C for 30 min or to boiling for 5 min. At room temperature at least 2 h are necessary to obtain a full and stable color. Heating is also disadvantageous because it increases the vaporization of toxic phenol vapors and it may lead to the formation of insoluble manganese dioxide, which interacts with the photometric determination. We found that the addition of ketones (preferably acetone) to the catalyst solution (MnSO4) accelerates the reaction in such a manner that heating is not necessary and the full color development can be obtained within 6 min. The proposed method is superior to the conventional ones because (1) the fully developed color can be obtained after 6 minutes without heating; (2) boiling, which increases the volatilization of phenol and creates dangers for the laboratory staff and the equipment, can now be reduced; and (3) the formation of manganese dioxide in the test solution is avoided.

Amides↗
PubMedDate not supplied

Application technique and slurry co-fermentation effects on ammonia, nitrous oxide, and methane emissions after spreading: I. Ammonia volatilization.

Ammonia emissions after spreading animal manure contribute a major share to N losses from agriculture. There is an increasing interest in anaerobic co-digestion of liquid manure with organic additives. This fermentation results in a change of physical and chemical parameters of the slurry. Among these are an increased pH and ammonium content, implying a higher risk of NH3 losses from fermentation products. To compare different application techniques and the effect of fermentation on NH3 volatilization, we used the standard comparison method and tested it for reliability. This method seems to be perfectly suited for experiments with a large number of treatments and replicates if prerequisites concerning the experimental layout are considered. We tested four different application techniques on arable and grassland sites. The more the substrate was incorporated into the soil or applied near the soil surface on the grassland site, the less NH3 was lost. Injection of the substrate reduced losses to less than 10% of applied NH4+ on both sites, whereas losses after splash plate application amounted to more than 30%. Trail shoe application on grassland performed as well as injection. Harrowing on arable land also reduced emissions efficiently, if harrowing occurred within the first 2 h after application. Emissions from trail hose-applied co-fermentation product were not greater than from unfermented slurry. Better infiltration of the less viscous substrate seemed to have compensated for the increased loss potential.

Ammonia↗
PubMed1976

[Single and complex effect of ammonia and hydrogen sulfide in the air on small laboratory animals (rats) under various environmental conditions 2. Effect of hydrogen sulfide alone and hydrogen sulfide with ammonia and dust].

The maximum tolerable concentrations per animal position of hydrogen sulphide alone (5 ppm) and with ammonia (5 ppm H2S; 30 ppm NH3) were established by model experiments under defined environmental conditions. The normal values of the contaminant gas combination were found to be acceptable even with additional dust load on the experimental animals. TGL 29084 should stipulate 5 ppm hydrogen sulphide as the new maximum concentration per animal position.

Ammonia↗
PubMed2006

Solvation of yttrium with ammonia revisited. Di-amide formation in the reaction of yttrium with ammonia.

The reactivity of yttrium atoms toward ammonia is revisited using expanded density functional theory calculations. The new results reveal that absorption of NH3 on YNH is dissociative to form Y(NH2)2. The di-amide species can adsorb further NH3 molecules molecularly to form Y(NH2)2NH3 and Y(NH2)2(NH3)2. The calculations aimed to reveal the detail of the potential energy curves between the imide and the di-amide forms. The Y(NH2)2(NH3)x species are more stable than those of YNH(NH3)x by more than 20 kcal/mol.

Journal Article↗
PubMed2006

Photoionization-induced dynamics of ammonia: ab initio potential energy surfaces and time-dependent wave packet calculations for the ammonia cation.

An analytical anharmonic six-dimensional three-sheeted potential energy surface for the ground and first excited states of the ammonia cation has been developed which is tailored to model the ultrafast photoinduced dynamics. Selected ab initio cuts, obtained by multireference configuration interaction calculations, have been used to determine the parameters of a diabatic representation for this Jahn-Teller and pseudo-Jahn-Teller system. The model includes higher-order coupling terms both for the Jahn-Teller and for the pseudo-Jahn-Teller matrix elements. The relaxation to the ground state is possible via dynamical pseudo-Jahn-Teller couplings involving the asymmetric bending and stretching coordinates. The photoelectron spectrum of NH3 and the internal conversion dynamics of NH3+ have been determined by wave packet propagation calculations employing the multiconfigurational time-dependent Hartree method. Three different time scales are found in the dynamics calculations for the second absorption band. The ultrafast Jahn-Teller dynamics of the two excited states occurs on a 5 fs time scale. The major part of the internal conversion to the ground state takes place within a short time scale of 20 fs. This fast internal conversion is, however, incomplete and the remaining excited state population does not decay completely even within 100 fs.

Journal Article↗
PubMed1989

Ammonia and thermotaxis: Further evidence for a central role of ammonia in the directed cell mass movements of Dictyostelium discoideum.

Evidence is presented to support the hypothesis that, in addition to its possible role in mediating chemo- and phototaxis, ammonia (NH(3)) is also the key substance responsible for directing thermotaxis of the migrating slugs of Dictyostelium discoideum. NH(3) is produced by the cells of the slug and we show that high and low concentrations of NH(3) decrease the speed of the amoebae while intermediate concentrations increase their speed. NH(3) production by amoebae is affected by temperature: the greater the temperature, the more NH(3) is produced. From these facts we speculate that both the positive and the negative thermotaxis found in slugs can be explained by temperature gradients stimulating regional differences in NH(3) production, and depending upon the temperature, the amount of NH(3) will either be in the range that stimulates or inhibits the rate of movement. If this explanation is correct, then minute localized differences in the production of NH(3) and their differential effect on cell speed could account for all the directed movements of the cell masses of these slime molds.

Journal Article↗
PubMed1984

Glutamic Acid metabolism and the photorespiratory nitrogen cycle in wheat leaves: metabolic consequences of elevated ammonia concentrations and of blocking ammonia assimilation.

The effects of methionine sulfoximine and ammonium chloride on [(14)C] glutamate metabolism in excised leaves of Triticum aestivum were investigated. Glutamine was the principal product derived from [U(14)C]glutamate in the light and in the absence of inhibitor or NH(4)Cl. Other amino acids, organic acids, sugars, sugar phosphates, and CO(2) became slightly radioactive. Ammonium chloride (10 mm) increased formation of [(14)C] glutamine, aspartate, citrate, and malate but decreased incorporation into 2-oxoglutarate, alanine, and (14)CO(2). Methionine sulfoximine (1 mm) suppressed glutamine synthesis, caused NH(3) to accumulate, increased metabolism of the added radioactive glutamate, decreased tissue levels of glutamate, and decreased incorporation of radioactivity into other amino acids. Methionine sulfoximine also caused most of the (14)C from [U-(14)C]glutamate to be incorporated into malate and succinate, whereas most of the (14)C from [1-(14)C]glutamate was metabolized to CO(2) and sugar phosphates. Thus, formation of radioactive organic acids in the presence of methionine sulfoximine does not take place indirectly through "dark" fixation of CO(2) released by degradation of glutamate when ammonia assimilation is blocked. When illuminated leaves supplied with [U-(14)C] glutamate without inhibitor or NH(4)Cl were transferred to darkness, there was increased metabolism of the glutamate to glutamine, aspartate, succinate, malate, and (14)CO(2). Darkening had little effect on the labeling pattern in leaves treated with methionine sulfoximine.

Journal Article↗
PubMed2000

Physical map location of the multicopy genes coding for ammonia monooxygenase and hydroxylamine oxidoreductase in the ammonia-oxidizing bacterium Nitrosomonas sp. strain ENI-11.

Pulsed-field gel electrophoresis of PmeI digests of the Nitrosomonas sp. strain ENI-11 chromosome produced four bands ranging from 1,200 to 480 kb in size. Southern hybridizations suggested that a 487-kb PmeI fragment contained two copies of the amoCAB genes, coding for ammonia monooxygenase (designated amoCAB(1) and amoCAB(2)), and three copies of the hao gene, coding for hydroxylamine oxidoreductase (hao(1), hao(2), and hao(3)). In this DNA fragment, amoCAB(1) and amoCAB(2) were about 390 kb apart, while hao(1), hao(2), and hao(3) were separated by at least about 100 kb from each other. Interestingly, hao(1) and hao(2) were located relatively close to amoCAB(1) and amoCAB(2), respectively. DNA sequence analysis revealed that hao(1) and hao(2) shared 160 identical nucleotides immediately upstream of each translation initiation codon. However, hao(3) showed only 30% nucleotide identity in the 160-bp corresponding region.

Chromosome Mapping↗