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 1,621 records · Page 90Linked to original sources
PubMed1976

The mechanism of action of ethanolamine ammonia-lyase, an adenosylcobalamin-dependent enzyme. The source of the third methyl hydrogen in the 5'-deoxyadenosine generated from the cofactor during catalysis.

Ethanolamine ammonia-lyase is an adenosylcobalamin-dependent enzyme which catalyzes the conversion of ethanolamine and propanolamine to ammonia and the corresponding aldehydes. A mechanism has been proposed for this and other adenosylcobalamin-dependent reactions which involves cleavage of the carbon-cobalt bond of the cofactor followed by abstraction of a substrate hydrogen atom by the adenosyl fragment to form 5'-deoxyadenosine. In support of this proposal, a previous study demonstrated that the deamination of propanolamine by ethanolamine ammonia-lyase is accompanied by the reversible cleavage of the carbon-cobalt bond of the cofactor, with the production of 5'-deoxyadenosine (Babior, B.M., Carty, T.J., and Abeles, R.H. (1974) J. Biol. Chem. 249, 1689-1695). The present study is concerned with the origin of the third hydrogen atom on the methyl group of the 5'-deoxyadenosine produced in that reaction. The 5'-deoxyadenosine isolated from an incubation mixture initially containing enzyme, [5',5'-D2]adenosylcobalamin, and [1,1-D2]propanolamine was chemically degraded so that the 4' and 5' carbon atoms were, respectively, converted to the carbonyl and methyl carbons of acetaldehyde. Analysis of the p-nitrophenylhydrazone of the acetaldehyde by gas-liquid chromatography-mass spectroscopy revealed 3 deuterium atoms/molecule, indicating that two of the methyl hydrogens originated from adenosylcobalamin and the third was donated by substrate. This observation provides further support for the participation of 5'-deoxyadenosine in the mechanism of adenosylcobalamin-dependent reactions.

Ammonia-Lyases↗
PubMed1992

Cerebral ammonia levels and enzyme changes during Plasmodium yoelii infection in mice.

Ammonia, lactate and glutamate levels and the activities of glutamine synthetase (GS), glutamate dehydrogenase (GDH), glutaminase (GLN), aspartate transaminase (AST), phosphofructokinase (PFK) and monoamine oxidase (MAO) were compared in the brain tissue of normal and P. yoelii infected mice. The brain lactate increased by 96% at peak parasitaemia. Cerebral ammonia also exhibited an increase in infected mice which was parasitaemia dependent, while glutamate remained almost unchanged. The brain glutamine synthetase registered an increase of 35% (P < 0.001) in post-mitochondrial fractions, this effect being perceptible even at low parasitaemia, but attained constancy at parasitaemia levels higher than 20%. The activity of monoamine oxidase and phosphofructokinase increased by 105% (P < 0.02) and 41% (P < 0.05) respectively while glutamate dehydrogenase decreased by 15% (P < 0.001). Glutaminase and aspartate transaminase were not significantly influenced by infection (tested only at high parasitaemia levels). It has been postulated that cerebral hypoxia and aberrations in ammonia metabolism may both contribute towards malaria induced cerebral complications.

Ammonia↗
PubMed1978

The mechanism of action of ethanolamine ammonia-lyase, an adenosylcobalamin-dependent enzyme. Reaction of the enzyme.cofactor complex with 2-aminoacetaldehyde.

Ethanolamine ammonia-lyase (EC 4.3.1.7) catalyzes the adenosylcobalamin-dependent deamination of ethanolamine and 2-aminopropanol. Incubation of the enzyme.cofactor complex with 2-aminoacetaldehyde leads to rapid cleavage of the carbon--cobalt bond accompanied by the destruction of the corrinoid portion of the cofactor. During this reaction the adenosyl portion of the cofactor is oxidized to 4',5'-anhydroadenosine, and the aminoacetaldehyde is converted to acetic acid, which remains associated with the enzyme as a noncovalent complex which survives gel filtration. There is no evidence for the alkylation of the corrin metal by the substrate analog. The enzyme.AdoCbl complex is thus able to eliminate an amino group from a substrate analog without the formation of a new alkyl cobalamin in which the analog is a ligand. These observations do not support the participation of what might be termed "substratylcobalamin" as an intermediate in the ammonia migration occurring in reactions catalyzed by ethanolamine ammonia-lyase.

Ammonia-Lyases↗
PubMed1983

Elicitor induction of mRNA activity. Rapid effects of elicitor on phenylalanine ammonia-lyase and chalcone synthase mRNA activities in bean cells.

Changes in the activity levels of mRNAs encoding phenylalanine ammonia-lyase and chalcone synthase, two characteristic enzymes of phenylpropanoid biosynthesis, in elicitor-treated cells of dwarf French bean (Phaseolus vulgaris L.) have been investigated by immunoprecipitation of [35S]methionine-labelled enzyme subunits synthesised in vitro in an mRNA-dependent rabbit reticulocyte lysate translation system. Elicitor heat-released from cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of bean, causes marked rapid increases in the polysomal activities of the mRNAs encoding the two enzymes concomitant with the phase of rapid increase in enzyme activity at the onset of phaseollin accumulation during the phytoalexin defence response. Increased polysomal mRNA activities encoding the two enzymes can be observed 30 min after elicitor treatment. The patterns of induction of the mRNA activities are broadly similar with respect to time and elicitor concentration although small but distinct differences between the enzymes were observed in the elicitor concentration giving maximum induction. There is a close correlation between the induction of polysomal mRNA activity and the induction of enzyme synthesis in vivo by elicitor treatment with respect to both the kinetics of induction and the dependence on elicitor concentration. The data indicate that elicitor stimulation of phenylalanine ammonia-lyase and chalcone synthase synthesis in vivo is largely a result of increased polysomal activity of the mRNAs encoding these enzymes. Similar patterns of induction of polysomal mRNA activity are observed with elicitor preparations from a variety of sources. The marked increases in polysomal mRNA activities encoding phenylalanine ammonia-lyase and chalcone synthase are increases as a proportion of total cellular mRNA activity, indicating that elicitor does not increase these polysomal mRNA activities by stimulation of selective recruitment from the total pool of cellular mRNA.

Acyltransferases↗
PubMed1979

Concomitant induction of phenylalanine ammonia-lyase and flavanone synthase mRNAs in irradiated plant cells.

Irradiation of previously dark-grown cell suspension cultures from parsley (Petroselinum hortense Hoffm.) with ultraviolet light caused large, concomitant increases in mRNA activities for two characteristic enzymes of phenylpropanoid metabolism, phenylalanine ammonia-lyase, and flavanone synthase. The rates of enzyme synthesis both in vitro in a reticulocyte lysate and in vivo were quantitated by direct immunoprecipitation of the labeled enzyme subunits. Following a period of about 2 h, during which possible changes were below the limits of detectability, the two mRNA activities increased rapidly in irradiated cells for serveral hours. Phenylalanine ammonia-lyase mRNA reached a peak in activity a few hours earlier than flavanone synthase mRNA. The apparent half-lives of the enzyme activities were about 7 to 10 h for phenylalanine ammonia-lyase and 5 to 7 h for flavanone synthase. These data were used to calculate the expected, light-induced changes in enzyme activity from the measured changes in mRNA activity. The results for both enzymes were in agreement with experimental data, indicating that the light-induced changes in enzyme activity can be explained by changes in the respective mRNA activity. Some data concerning changes in the degree of polyadenylation of the mRNAs and the inhibitory effects of 7-methylguanosine 5'-phosphate are presented.

Acyltransferases↗
PubMed1993

Glutamine inhibits the ammonia-dependent activities of two Cys-1 mutants of human asparagine synthetase through the formation of an abortive complex.

Cys-1 mutants of recombinant human asparagine synthetase were constructed and their ability to catalyze the glutamine-dependent nitrogen transfer reaction required for asparagine biosynthesis was determined. In agreement with previous work, altering Cys-1 to either Ala or Ser eliminated the glutamine-dependent activity while only minimally affecting the kinetic properties of the ammonia-dependent reaction. A lack of glutaminase activity in these mutants also allowed examination of glutamine binding in studies of the ability of glutamine to inhibit the ammonia-dependent production of asparagine. In both mutants, analysis of the observed kinetics indicated that glutamine inhibited ammonia-dependent asparagine synthesis through the formation of an abortive complex. This unanticipated observation suggests that the commonly accepted mechanism for nitrogen transfer from the primary amide of glutamine to aspartic acid in asparagine synthetase may have to be re-examined. A novel mechanistic proposal which is consistent with the formation of an abortive complex in the two Cys-1 mutants is presented.

Ammonia↗
PubMed1980

Acute and chronic effects of ammonia burns on the respiratory tract.

Exposure to anhydrous ammonia can result in substantial injury to the respiratory system, eyes, and integument. In this retrospective study, we present the acute and chronic respiratory manifestations in 12 patients exposed to anhydrous ammonia as a result of the same accident. Survivors suffering significant ill effects are separated into two groups according to history and clinical course. One group of patients sustained exposure to high concentrations of ammonia over a short period of time. They manifested upper airway obstruction and required early intubation or tracheostomy. These patients recovered with few pulmonary sequelae and are presently in good pulmonary health. The second group of patients were exposed to lower concentrations of gas over a prolonged period of time and did not manifest upper airway obstruction. In this group of patients, however, significant long-term pulmonary sequelae are manifested.

Adolescent↗
PubMed1998

Quantification of ammonia in human breath by the selected ion flow tube analytical method using H30+ and 02+ precursor ions.

We show how our selected ion flow tube mass spectrometric technique for trace gas analysis can be used to determine the concentrations of ammonia in alveolar breath from single exhalations using both H30+ and 02+ precursor ions for chemical ionization. Thus, data are presented of the alveolar ammonia concentrations in the breath of six healthy volunteers following the ingestion of a liquid protein meal, which show that consistent values are obtained using these two precursor ions. Alveolar breath ammonia concentrations (which range from 200 to 1750 ppb in these individuals) are compared with those obtained from bag samples of breath from the same individuals.

Ammonia↗
PubMed2005

Photocatalytic degradation of high ammonia concentration water solutions by TiO2.

Recent studies reported the use of suspended TiO2 powder as photo catalyst in the degradation process of several organic and inorganic substances in water, like chlorinated hydrocarbons, alkyl- and alkanoloammines and ammonia. In order to evaluate the possibility of using this method for a further removal of ammonia from wastewater after a biological nitrification/denitrification treatment, a kinetic study of photo oxidation over TiO2 of NH3/NH4 in the high concentration range of 26 - 214 mg/I, has been carried out. Effects of pH, TiO2, ammonium and dissolved O2 concentration on the degradation efficiency and reaction products distribution (NO2-, NO3- e N2) were studied. The results have shown that, at a catalyst concentration of 0.012% (p/v), the photo catalytic oxidation of ammonia can be described with the Langumuir- Hinshelwood kinetic model, as reported by several authors.

Ammonia↗
PubMed1978

Cerebral blood flow and metabolism in chronically hyperammonemic rats: effect of an acute ammonia challenge.

The effects of chronic hyperammonemia on cerebral metabolism were studied in rats four and eight weeks after the construction of a portacaval shunt. Compared to sham-operated controls, shunted animals had increased arterial concentrations of ammonia and glutamine and decreased glutamate. Cerebral blood flow, measured by xenon 133 washout in animals lightly anesthetized with nitrous oxide, increased from a control of 91 +/- 5 (mean +/- SEM) to 139 +/- 20 ml per 100 gm tissue per minute after shunting for eight weeks; however, the cerebral metabolic rate for oxygen was not different from control four or eight weeks after the shunting procedure. Following intraperitoneal administration of a small ammonium acetate load (2.6 mmol/kg), eight-week portacaval animals consistently underwent a fall in cerebral blood flow and cerebral oxygen consumption and developed high-voltage slow waves in the electroencephalogram. Glutamine was produced by the brains of all groups of animals; the cerebral metabolic rate for glutamine was greater than control in eight-week portacaval rats, the only animals to show a net uptake of ammonia into brain. The findings suggest that increased cerebral sensitivity to ammonia, along with nonspecific effects of chronic portal-systemic shunting, may lead to uncoupling of cerebral blood flow and oxidative metabolism.

Ammonia↗
PubMed1979

Cellulase production and ammonia metabolism in Trichoderma reesei on high levels of cellulose.

Trichoderma can be cultured in stirred-tank fermentors on high (8%) cellulose concentrations without increasing the salt concentration of the medium when NH4OH is used to control pH and as a nitrogen source. Approximately 90% of the ammonia consumed by the organism can be added as NH4OH. The advantage of using high concentrations of cellulose is that culture filtrates with greater cellulase activity are obtained. The advantage of a low salts medium is that unwanted solutes in the final enzyme preparation are reduced. The appearance of cellulase in the medium occurs later than net ammonia uptake so that only 20% of the final amount of cellulase has appeared when 80% of the maximum amount of ammonia has been consumed.

Ammonia↗
PubMed1977

Ammonia absorption from the canine colon after portacaval shunt.

Ammonia absorption was studied from Thirty-Vella colon loops in 6 dogs. Four underwent an end-to-side portacaval shunt and it was shown that absorption of ammonia from the colon significantly increased postoperatively. Absorption of ammonia from various solutions was also measured before and after portacaval shunt and it was shown taht absorption was increased from a high pH solution and from a solution with a high bicarbonate content and reduced from a low pH, low osmolality and high osmolality solution. Increased deposits of stainable iron were demonstrated in the livers of dogs following portacaval shunt.

Ammonia↗
PubMed1991

Glutamine-enhanced enteral diet improves nitrogen balance without increasing portal ammonia.

Following surgical stress the jejunum actively metabolizes endogenous glutamine, a non-essential amino acid, to produce alanine and ammonia, which augments substrate flow to the liver at a time when oral intake of nutrients is decreased. Oral glutamine supplementation theoretically may modify the response to injury. This study was designed to demonstrate the role of the jejunum in postinjury glutamine metabolism and to evaluate the influence of enteral glutamine supplements on nitrogen and ammonia metabolism after laparotomy and bowel resection in dogs. Oral glutamine in the presence of an intact small bowel significantly improved nitrogen balance (461 mg kg body-weight-1 day-1) compared with a control diet (-370 mg kg-1 day-1) (P less than 0.05, analysis of variance). Removal of the proximal small bowel prevented this beneficial effect of glutamine (-507 mg kg-1 day-1). Glutamine-supplemented and control diets were associated with similar portal ammonia concentrations throughout the study.

Ammonia↗
PubMed1988

Characterization of trichothecenes by tandem mass spectrometry using reactive collisions with ammonia.

The use of low-energy (7 eV Elab) reactive collisions with ammonia provides a highly specific method for the characterization of trichothecenes since the collisions between the protonated molecule and ammonia not only produce ions formed by collisionally activated dissociation but ammonium adduct ions and ions formed by substitution reactions. The good detection limits (20-300 pg) and good quantitative reproducibility (relative standard deviations are 5-10%) mean that the use of reactive collisions with ammonia is also very suitable for monitoring and quantitative analyses.

Ammonia↗
PubMed1996

Glutamine, myo-inositol, and organic brain osmolytes after portocaval anastomosis in the rat: implications for ammonia-induced brain edema.

Brain myo-inositol, an organic osmolyte, is decreased in cirrhotic patients with hepatic encephalopathy but appears unchanged in fulminant hepatic failure. An osmoregulatory response to the increase in brain glutamine may explain the decrease in brain myo-inositol; if this is the case, organic osmolytes may account for differences in the development of brain edema seen in acute or chronic liver failure. The response of myo-inositol and nine other organic osmolytes to the increase in brain glutamine at different time intervals after portacaval anastomosis (PCA) in the rat was studied. Organic osmolytes were measured in brain tissue and cerebrospinal fluid. Water in cerebral cortex was measured after ammonia infusion with the gravimetric method. Six weeks after PCA, despite an increase in brain glutamine (PCA, 16.4 +/- 2 mmol.kg wt-1.kg wt-1; sham, 5 +/- 1 mmol.L-1.kg wt-1), the content of total organic osmolytes did not increase (PCA, 44.1 +/- 3; sham, 43 +/- 4) because of a decrease of other osmolytes (myo-inositol, 54%; urea, 39%; taurine, 33%; and glutamate, 8%). Brain myo-inositol was lower at 3 weeks (3.4 +/- 0.5 kg wt-1) than at 1 day after PCA (4.7 +/- 0.5 kg wt-1). An ammonia infusion resulted in brain edema at both time points. In conclusion, the reduction in brain myo-inositol in PCA rats is accompanied by the decrease of other organic osmolytes, supporting the view that changes in myo-inositol reflect an osmoregulatory response. The decrease in brain myo-inositol is more marked as time elapses after PCA. In a model in which short-term and large doses of ammonia were infused, the decrease in brain myo-inositol did not prevent the development of brain swelling. Understanding brain osmoregulatory mechanisms may provide new insights into hepatic encephalopathy and brain edema in fulminant hepatic failure.

Ammonia↗
PubMed1981

Effects of ammonia on liver lysosomal functionality in Salmo gairdneri Rich.

Salmo gairdneri specimens were exposed for 4-48 hours to three different concentrations of un-ionized ammonia (UIA). An increase in lysosomal sensitivity to osmotic shock and in total proteolytic activity occurs in the liver. The amount of this increase depends upon the exposure time or upon environmental and tissue ammonia levels. On the other hand ammonia does not affect lysosome hydrolases activity in vitro.

Ammonia↗
PubMed1989

Do amiloride and ouabain affect ammonia fluxes in perfused Carcinus gill epithelia?

The effects of inhibitors on the efflux of ammonia (from the basolateral to the apical side, Jb----a) were studied in preparation of isolated Carcinus gills immersed in dilute seawater (DSW) that was identical to the perfusion solution. Adding 10(-4) M amiloride to the solution bathing the gill preparations reduces the efflux of ammonia by 29% relative to the control value. Under experimental conditions, it appears that only about 1% of the amiloride-sensitive influx of Na+ (Ja----b) can be exchanged with NH4+ on an equimolar basis. The ammonium ion is apparently transported at the basolateral side by a carrier-mediated process. Kinetic analyses of the influx of ammonium ions revealed a Km of 36.99 microM and a maximum velocity (Vmax) equal to 19.6 mumol g-1.h-1. Basolaterally applied ouabain (5 x 10(-3) M) and NaCN (10(-3) M) reduced the efflux of ammonia by 46.7 and 42.2%, respectively, suggesting an interaction of NH4+ with the basolaterally located Na+/K+ exchanger in which NH4+ appears to be able to substitute for K+.

Amiloride↗
PubMed1980

Hippocampal glutamate release after porta cava anastomosis: reduced sensitivity to ammonia inhibition.

In vitro measurements of basal efflux and evoked release of exogenous and endogenous glutamate from rat hippocampus showed that exposition of the tissue to pathophysiological concentrations of ammonium chloride (3 mM) for 40--60 min abolished the KCl-induced release of endogenous glutamate. Basal efflux of endogenous glutamate was elevated by ammonium chloride with a delay of 30--40 min. In an attempt to link these observations to the pathogenesis of hepatic coma, rats were subjected to porta-cava anastomosis, and the hippocampal tissue was tested for ammonia sensitivity 3--4 weeks after the operation. The results showed that ammonia perfusion of the tissue was without effect effect on either basal or KCl-evoked release of endogenous glutamate. In addition, the utilization of glutamine for glutamate formation was influenced in hippocampal but not cortical tissue form porta-cava anastomized rats. The results suggest that ammonia is an important factor for the disturbed metabolism of the neurotransmitter pool of glutamate in hepatic failure.

Ammonia↗