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 1,243 records · Page 69Linked to original sources
PubMed1979

Superinduction of phenylalanine ammonia-lyase in gherkin hypocotyls caused by the inhibitor, L-alpha-aminooxy-beta-phenylpropionic acid.

The extractable activity of L-phenylalanine ammonia-lyase (EC 4.3.1.5) and the concentration of sugar esters of p-coumaric and ferulic acids in the hypocotyls of etiolated gherkin seedlings increase upon irradiation with white light. Treatment of intact seedlings with the phenylalanine ammonia-lyase inhibitors alpha-aminooxyacetic acid and L-alpha-aminooxy-beta-phenylpropionic acid during illumination causes enhanced formation of the lyase and reduces the accumulation of hydroxycinnamic acids. Enzyme activity in excised hypocotyl segments floating on buffer increases in the dark as well as in the light, while hydroxycinnamic acids accumulate only in the light. Phenylalanine ammonia-lyase formation in the segments is inhibited by cinnamic acid and, to a lesser extent, p-coumaric acid, while it is slightly enhanced by caffeic acid and is not affected by ferulic acid. Aminooxyphenylpropionate dramatically promotes phenylalanine ammonia-lyase formation in the segments in darkness and light prevents the accumulation of hydroxycinnamic acids in the light. Aminooxyphenylpropionate does not, however, affect the time course of apparent lyase formation and decay. Cinnamic acid, the product of the lyase reaction, antagonizes the effect of aminooxyphenylpropionate. It is proposed that the reaction product(s) are involved to some extent in the regulation of the pool of active lyase in the hypocotyl tissue.

Aminooxyacetic Acid↗
PubMed1980

Elicitor modulation of the turnover of L-phenylalanine ammonia-lyase in French bean cell suspension cultures.

(1) The mechanisms underlying the transient increase in phenylalanine ammonia-lyase activity during phaseollin accumulation in cell suspension cultures of Dwarf French bean (Phaseolus volgaris) have been investigated using density labelling with 3H from 2H2O coupled with residual analysis of the equilibrium distribution of enzyme activity in high-resolution KBr density gradients. (2) The resolution achieved in this system is sufficient to allow quantitative analysis of the relative proportions of light, unlabelled, pre-existing enzyme and heavy, labelled, newly synthesised enzyme. (3) Elicitor released by heat treatment of cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of French bean, caused a marked but transient increase in phenylalanine ammonia-lyase activity concomitant with the onset of phaseollin accumulation in the bean cultures. The induction of enzyme activity was highly dependent on elicitor concentration, with maximum induction occurring in two discrete concentration ranges; at an intermediate elicitor concentration, or at supra-optimal elicitor concentrations, no enzyme induction was observed. (4) At low concentrations of elicitor the induction of enzyme was entirely a result of elicitor stimulation of the rate of de novo enzyme production. In contrast, at higher elicitor concentrations the increase in enzyme activity was accompanied by a marked apparent stabilization of the enzyme in vivo, and the rapid but transient increase in enzyme activity was achieved by a programme of reciprocal changes in the rate constant for de novo enzyme production and the rate constant for removal of enzyme activity. Such reciprocal control of the rates of enzyme production and removal may be crucial in determining the magnitude and duration of the phytoalexin defense response. (5) Information on the specific activity of 2H label in the amino acid pools was obtained from analysis of the equilibrium distribution of residual, labelled activity. This showed directly that the turnover of the amino acid pools was fast relative to the turnover of phenylalanine ammonia-lyase and, hence, the rate of enzyme labelling was not limited by the rate of labelling of the amino acid pools. Elicitor treatment had no effect on the specific activity of label in the amino acid pools from which phenylalanine ammonia-lyase is synthesised.

Amino Acids↗
PubMed1981

Density labelling characterisation of the effects of cordycepin and cycloheximide on the turnover of phenylalanine ammonia-lyase.

L-Phenylalanine ammonia-lyase (EC 4.3.1.5) undergoes a transient increase in activity in illuminated disc of Solanum tuberosum tuber parenchyme. Cycloheximide and cordycepin inhibit the initial increase in enzyme activity, but if addition of these anti-metabolites is delayed until the time of maximum enzyme levels, the subsequent decline in enzyme activity is inhibited (Lamb, C.J. (1977) Planta, 135, 169-175). The effect of delayed treatment with cycloheximide or cordycepin on the turnover of phenylalanine ammonia-lyase has been analysed by density labelling with 2H from 2H2O. Delayed introduction of cycloheximide or cordycepin reduces the rate of labelling of phenylalanine ammonia-lyase whilst preventing the decay in enzyme activity observed in controls not treated with inhibitor, and this labelling pattern cannot be accounted for by effects of cycloheximide or cordecypin on the labelling of amino acid pools. It is concluded that delayed treatment with cycloheximide or cordycepin leads to the maintenance of high levels of phenylalanine ammonia-lyase by inhibition of the removal of active enzyme rather than by maintenance of high rates of enzyme synthesis.

Ammonia-Lyases↗
PubMed1985

[13N]Ammonia and L-[amide-13N]glutamine metabolism in glutaminase-sensitive and glutaminase-resistant murine tumors.

The short-term metabolic fate of labeled nitrogen derived from [13N]ammonia or from L-[amide-13N]glutamine was determined in murine tumors known to be resistant (Ridgeway Osteogenic Sarcoma (ROS] or sensitive (Sarcoma-180 (S-180)) to glutaminase therapy. At 5 min after intraperitoneal injection of [13N]ammonia or of L-[amide-13N]glutamine, only about 0.7% of the label recovered in both tumors was in protein and nucleic acid. After [13N]ammonia administration, most of the label (over 80%) was in a metabolized form; a large portion of this metabolized label (50-57%) was in the urea fraction with a smaller amount in glutamine (37-42%). The major short-term fate of label derived from L-[amide-13N]glutamine was incorporation into components of the urea cycle with smaller amounts in the acidic metabolites and in acidic amino acids. No labeled urea was found during in vitro studies in which S-180 tumor slices were incubated with [13N]ammonia, suggesting that the [13N]urea formed in the tumor in the in vivo experiments was not due to de novo synthesis through carbamyl phosphate in the tumor. Both tumors exhibited very low glutamine synthetase activity. Following glutaminase treatment, glutamine synthetase and gamma-glutamyltransferase activities, while remaining low, increased in the resistant tumor but not in the sensitive tumor; this increase may be related to the insensitivity of the ROS tumor toward glutaminase treatment.

Amino Acids↗
PubMed2006

Direct molecular and spectroscopic evidence for increased ammonia removal capacity of skeletal muscle in acute liver failure.

BACKGROUND/AIMS: It has been proposed that, in acute liver failure, skeletal muscle adapts to become the principle organ responsible for removal of blood-borne ammonia by increasing glutamine synthesis, a reaction that is catalyzed by the cytosolic ATP-dependent enzyme glutamine synthetase. To address this issue, glutamine synthetase expression and activities were measured in skeletal muscle of rats with acute liver failure resulting from hepatic devascularization. METHODS: Glutamine synthetase protein and gene expression were investigated using immunoblotting and semi-quantitative RT-PCR analysis. Glutamine synthetase activity and glutamine de novo synthesis were measured using, respectively, a standard enzymatic assay and [13C]-nuclear magnetic resonance spectroscopy. RESULTS: Glutamine synthetase protein (but not gene) expression and enzyme activities were significantly up-regulated leading to increased de novo synthesis of glutamine and increased skeletal muscle capacity for ammonia removal in acute liver failure. In contrast to skeletal muscle, expression and activities of glutamine synthetase in the brain were significantly decreased. CONCLUSIONS: These findings demonstrate that skeletal muscle adapts, through a rapid induction of glutamine synthetase, to increase its capacity for removal of blood-borne ammonia in acute liver failure. Maintenance of muscle mass together with the development of agents with the capacity to stimulate muscle glutamine synthetase could provide effective ammonia-lowering strategies in this disorder.

Ammonia↗
PubMed1983

Ammonia and acid-base homeostasis.

The metabolic pathways involved in renal ammonia production have been considered and potential sites of regulatory control have been delineated. New information that acute acidosis stimulates renal ammonia production and that chronic respiratory acidosis does not result in an adaptive increase in the renal capacity to produce ammonia has been emphasized. The effect of potassium on renal ammonia production and the physiologic and pathophysiologic implication of this relationship have been detailed. Finally, the mechanism of urinary ammonium excretion and the impact of altered ammoniagenesis on urinary acidification, and the interpretation of clinical acidification tests have been discussed.

Acid-Base Equilibrium↗
PubMed1985

Studies of the ammonia-dependent reaction of beef pancreatic asparagine synthetase.

We have studied the asparagine synthetase reaction with regard to the ammonia-dependent production of asparagine. Hydroxylamine was shown to be an alternate substrate for the asparagine synthetase reaction, and some of its kinetic properties were examined. The ammonia-dependent reaction was examined with regard to inhibition by asparagine. It was found that asparagine inhibition was partial competitive with respect to ammonia, regardless of the concentration of aspartate. However, when MgATP was not saturating, the inhibition by asparagine became linear competitive. These results were interpreted to be consistent with a kinetic mechanism for asparagine synthetase where ammonia is bound to the enzyme followed by MgATP causing asparagine release.

Ammonia↗
PubMed1981

The effect of proteinases on phenylalanine ammonia-lyase from the yeast Rhodotorula glutinis.

Phenylalanine ammonia-lyase (EC 4.3.1.5) of the yeast Rhodotorula glutinis was rapidly inactivated by duodenal juice. It was susceptible to chymotrypsin and subtilisin and to a lesser extent trypsin. Initial proteolysis of the enzyme by chymotrypsin and trypsin resulted in cleavage of the monomeric subunit (75 000 Mr) into a large (65 000 Mr) and a small (10 000 Mr) peptide. The small peptide was rapidly degraded. The 65 000-Mr fragment was resistant to prolonged incubation with chymotrypsin, but was degraded by trypsin under the same conditions. Phenylalanine ammonia-lyase was cleaved into several polypeptides by subtilisin, the 65 000-Mr peptide being totally absent. The N-terminal region of the enzyme was contained in the 65 000-Mr fragment, as was the dehydroalanine moiety, the prosthetic group. Active-site-binding ligands protect the enzyme from inactivation by the three proteinases, and peptide-bond cleavage by trypsin and chymotrypsin. Several chemical modifications were performed on phenylalanine ammonia-lyase. Some decreased its antigenicity, and ethyl acetimidate decreased the rate of degradation of the 65 000-Mr peptide by trypsin. The modification did not protect the enzyme from proteolytic inactivation of the enzymic activity. These observations are discussed in terms of the structure of phenylalanine ammonia-lyase and site of action of the proteinases.

Ammonia-Lyases↗
PubMed1989

Incorporation of intraportally infused [15N]ammonia into urinary uric acid in cockerels pretreated with methionine sulfoximine.

1. Measurements were made in situ to determine the incorporation of intraportally infused ammonia-15N into urinary uric acid in cockerels pre-treated with methionine sulfoximine (MSM), a glutamine synthetase inhibitor. 2. The incorporation of 15N into urinary uric acid was 34% of the infused amount in MSM-treated birds. This was not significantly different from the value of 46% for control birds. 3. Pre-treatment with MSM inhibited the activity of liver glutamine synthetase to 7% of the control value and decreased the incorporation of the infused ammonia-15N into plasma glutamine amide-N to 3% of the control. 4. Increases in glutamine concentrations in the blood, liver and kidney caused by the infusion of ammonia were also completely inhibited by the MSM treatment (P less than 0.05). 5. It is concluded that in the cockerel ammonia-N can be incorporated into uric acid other than by glutamine formation.

Ammonia↗
PubMed1951

Relative concentrations of N15 in urinary ammonia N and urea N after feeding N15-labeled compounds.

Available data on the isotopic ratio See PDF for Equation of ammonia (r(a)) and that of urea (r(u)) after a single feeding of glycine, aspartic acid, and ammonium citrate are analyzed. From this analysis the following conclusions are drawn. 1. The isotopic ratio See PDF for Equation of ammonia (r(a)) is always higher than that of urea (r(u)) in the initial period after a single feeding of isotopic glycine or aspartic acid, but the relation is reversed later. A similar relation probably holds after feeding isotopic ammonia. 2. It is pointed out that the ratio of average r(a) to average r(u) depends on the time interval for which urine is collected, on the schedule of feeding, and probably also on the amount taken at each feeding. When the amount fed and the feeding schedule are unknown, theoretical interpretation of the ratio of average r(u) to average r(u) is impossible. 3. At the point of maximum isotopic ratio of urea, it is very probably equal to the isotopic ratio of ammonia. A possible explanation is suggested.

Ammonia↗
PubMed1976

Wound-induced phenylalanine ammonia-lyase in potato tuber tissue. Development of enzyme activity and effects of antibiotics.

Phenylalanine ammonia-lyase [EC 4.3.1.5.] activity increased rapidly after a 3-hr lag period in potato tuber (Solanum tuberosum L. cv. May Queen) disks incubated in a suitable medium in the dark at 25 degrees. The activity reached a maxinum after incubation for about 40 hr. The effects of actinomycin D, 6-methylpurine, cycloheximide, chloramphenicol, and mitomycin C on the induction of phenylalanine ammonia-lyase were investigated during incubation of the disks. Actinomycin D, 6-methylpurine, and cycloheximide all inhibited the formation of phenylalanine ammonia-lyase, though cycloheximide was the most effective at low concentrations. Application of actinomycin D for the initial lag period (3 hr) caused strong inhibition; however, if it was supplied later it did not inhibit but actually increased phenylalanine ammonialyase formation. In contrast, cycloheximide was effective over most of the incubation period. Chloramphenicol and mitomycin C did not inhibit phenylalanine phenylalanine ammonialyase induction, but markedly stimulated it. Light was not an essential factor for phenylalanine ammonia-lyase induction in the wounded tissue.

Ammonia-Lyases↗
PubMed2004

Structural basis for the entrance into the phenylpropanoid metabolism catalyzed by phenylalanine ammonia-lyase.

Because of its key role in secondary phenylpropanoid metabolism, Phe ammonia-lyase is one of the most extensively studied plant enzymes. To provide a basis for detailed structure-function studies, the enzyme from parsley (Petroselinum crispum) was crystallized, and the structure was elucidated at 1.7-A resolution. It contains the unusual electrophilic 4-methylidene-imidazole-5-one group, which is derived from a tripeptide segment in two autocatalytic dehydration reactions. The enzyme resembles His ammonia-lyase from the general His degradation pathway but contains 207 additional residues, mainly in an N-terminal extension rigidifying a domain interface and in an inserted alpha-helical domain restricting the access to the active center. Presumably, Phe ammonia-lyase developed from His ammonia-lyase when fungi and plants diverged from the other kingdoms. A pathway of the catalyzed reaction is proposed in agreement with established biochemical data. The inactivation of the enzyme by a nucleophile is described in detail.

Amino Acid Sequence↗
PubMed1976

Light-induced enzyme synthesis in cell suspension cultures of Petroselinum hortense. Demonstration in a heterologous cell-free system of rapid changes in the rate of phenylalanine ammonia-lyase synthesis.

The conditions for protein synthesis in vitro with polyribosomes from cell suspension cultures of parsel (Petroselinum hortense) and a wheat-germ extract were investigated. Two different criteria were used as estimated of the translational activity: (a) the total rate of incorporation of [35S]methionine into acid-insoluble material; (b) the ratio of large (molecular weight greater than 25000) to small (molecular weight less than 25000) peptide products. Depending on which of the criteria was employed, the pH optimum and the optimal concentrations for Tris=acetate, magnesium acetate, KCL, methionine and the wheat-germ extract differed considerably. The translational activity of the polyribosomes (both criteria) was effciently protected by 0.1 M Mg2+ against degradation during the isolation procedure. The rate of synthesis of phenylalanine ammonia-lyase in vitro with the polyribosomes was determined by measuring the incorporation rate of L-[35S]methionine into protein which was precipitable by a rabbit antiserum prepared for the purified enzyme. The immunoprecipitate was analyzed by disc gel electrophoresis in the presence of dodecylsulfate and was shown to contain small amounts of the complete enzyme subunits and relatively large amounts of shorter peptides which were also characteristic for the enzyme. The time course of light-induced changes in the rate of phenylalanine ammonia-lyase synthesis in vitro were investigated during a period of 15 h under two different conditions of induction: the cell cultures were irradiated with ultraviolet light eith (A) continuously or (B) for 2.5 h and then returned to darkness. Although the highest rate of enzyme synthesis was observed somewhat later inexperiment A than in experiment B, the periods of time during which the rate of synthesis increased rapidly were limited in both cases to only a few hours. The results obtained in vitro were identical within the limits of the experimental error with theoretical calculations of the changes in the rate constant of phenylalanine ammonia-lyase synthesis in vivo. These changes were calculated from the corresponding curves for the changes in the enzyme activity under the conditions of induction. The results are in agreement with previous observations suggesting that the induction of phenylalanine ammonia-lyase by light in the parsley cells was a short-term effect whose efficiency was greatly reduced within the 15 h of experimentation, even under continuous irradiation.

Ammonia-Lyases↗
PubMed1982

Regulation of L-phenylalanine ammonia-lyase by L-phenylalanine and nitrogen in Neurospora crassa.

Neurospora crassa possesses an inducible L-phenylalanine ammonia-lyase that is expressed only when cells are derepressed for nitrogen in the presence of L-phenylalanine. Enzyme synthesis requires both induction by L-phenylalanine and simultaneous nitrogen catabolite derepression. Carbon limitation in the presence of phenylalanine does not elicit induction of L-phenylalanine ammonia-lyase. Specific induction by L-phenylalanine is required, and other amino acids completely failed to induce any lyase activity. The nit-2 gene is a major regulatory locus which is believed to mediate nitrogen catabolite repression in Neurospora. Mutants of nit-2 fail to express any phenylalanine ammonia-lyase activity under conditions of derepression and induction which lead to good enzyme induction in the wild type and in nit-2 revertants. The loss of lyase activity in nit-2 mutants does not result from inducer exclusion, which suggests that the nit-2 gene product has a direct role in controlling the expression of this enzyme. Substantial amounts of the enzyme were detected in the growth medium as well as in cell extracts. Inhibitors of protein synthesis or RNA synthesis block the induction of L-phenylalanine ammonia-lyase, suggesting that expression of this enzyme is controlled at the level of transcription.

Ammonia-Lyases↗
PubMed1995

The concentration of ammonia regulates nitrogen metabolism in Saccharomyces cerevisiae.

Saccharomyces cerevisiae was grown in a continuous culture at a single dilution rate with input ammonia concentrations whose effects ranged from nitrogen limitation to nitrogen excess and glucose limitation. The rate of ammonia assimilation (in millimoles per gram of cells per hour) was approximately constant. Increased extracellular ammonia concentrations are correlated with increased intracellular glutamate and glutamine concentrations, increases in levels of NAD-dependent glutamate dehydrogenase activity and its mRNA (gene GDH2), and decreases in levels of NADPH-dependent glutamate dehydrogenase activity and its mRNA (gene GDH1), as well as decreases in the levels of mRNA for the amino acid permease-encoding genes GAP1 and PUT4. The governing factor of nitrogen metabolism might be the concentration of ammonia rather than its flux.

Amino Acid Transport Systems↗
PubMed1984

Mechanism of arginine protection against ammonia intoxication in the rat.

To examine the beneficial effect of arginine on ammonia intoxication, rats were injected intraperitoneally with a single dose of NH4Cl (6.75 mmol/kg) with and without arginine (5.0 mmol/kg) or ornithine (5.0 mmol/kg). Arginine or ornithine reduced the blood ammonia nitrogen at 30 min after NH4Cl injection from 3,288 +/- 800 micrograms/dl (mean +/- SE) to 538 +/- 90 and 575 +/- 34 micrograms/dl, respectively. In rats administered this dose of NH4Cl, arginine or ornithine did not increase further the hepatic carbamoyl-phosphate synthetase (EC 6.3.4.16) activation by N-acetylglutamate beyond the effect of NH4Cl. However, arginine or ornithine did increase the hepatic citrulline and urea content as well as the plasma urea concentration in these NH4Cl-injected rats. In rats injected with four doses of NH4Cl (2.5 mmol/kg), arginine or ornithine pretreatment increased the urea excretion and normalized the orotic acid excretion. These results indicate that arginine mitigates ammonia intoxication in the rat by increasing ornithine carbamoyltransferase activity through increased ornithine availability and not via activation of N-acetylglutamate synthetase. By increasing ornithine carbamoyltransferase activity, ornithine enhances the conversion of ammonia to citrulline and urea.

Acetyltransferases↗
PubMed1977

Enzymes of ammonia detoxication after portacaval shunt in the rat. I. Carbamylphosphate synthetase and aspartate transcarbamylase.

At high systemic blood concentrations ammonia may be partially deviated into the pathway of pyrimidine synthesis, as has been observed in different genetic defects of the urea cycle. The portacaval shunt (PCS) rat presents an animal model to study ammonia detoxication without an underlying enzyme defect in the urea cycle. Since ammonia may induce a deviation into the pyrimidine pathway by influencing enzymatic reactions involved in this pathway, the activity of carbamylphosphate synthetase and aspartate transcarbamylase in liver as well as the excretion of orotic acid in the urine were measured in rats 10, 20 and 30 days after PCS. The results suggest that in this experimental model ammonia may be channeled into the pyrimidine pathway leading to a stimulation of the first enzymatic step and to an increased excretion of orotic acid.

Ammonia↗
PubMed2004

Dogmas and controversies in the handling of nitrogenous wastes: ureotely and ammonia tolerance in early life stages of the gulf toadfish, Opsanus beta.

The marine gulf toadfish (Opsanus beta) is an unusual teleost fish as it is able to switch between ammoniotelism and ureotelism in response to a variety of laboratory conditions. The present study integrates field work conducted in Biscayne and Florida Bays, USA with laboratory studies to examine ureotelism during the early life history stages of O. beta. Adult toadfish voluntarily nested in artificial shelters placed amongst seagrass beds and were found to be predominantly ureotelic under natural conditions as the internal shelter water had mean urea and ammonia concentrations (N=51) of 14.2+/-1.6 micro mol N l(-1) and 8.9+/-0.9 micro mol N l(-1), respectively. Toadfish successfully spawned in shelters, providing eggs, larvae and juvenile toadfish for laboratory study. In the lab, juvenile toadfish were also ureotelic and urea was excreted in pulsatile events that accounted for 62.0+/-5.9% of total urea-N excreted. Excretion rates of urea-N and ammonia-N were 1.018+/-0.084 micro mol N h(-1) g(-1) and 0.235+/-0.095 micro mol N h(-1) g(-1), respectively. Field-collected eggs, larvae and juveniles expressed significant levels of the ornithine-urea cycle enzymes carbamoyl-phosphate synthetase III, ornithine transcarbamylase and arginase and the accessory enzyme glutamine synthetase, all of which increased in activity as toadfish developed through early life stages. In juveniles, the ammonia 96-h LC(50) value was 875 micro mol N l(-1) and there was a 3-fold increase in ornithine transcarbamylase activity in the 1000 micro mol N l(-1) NH(4)Cl treatment. The results are discussed in the context of the causal factor(s) for ureotelism in toadfish. Furthermore, the results of this study suggest it is unlikely that the adaptive significance of ureotelism in toadfish is a means to prevent fouling nests with ammonia and in turn poisoning offspring; however, additional study is warranted.

Ammonia↗