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PubMed1990

Ammonia (C-Methylamine) Transport across the Bacteroid and Peribacteroid Membranes of Soybean Root Nodules.

[(14)C]Methylamine (MA; an analog of ammonia) was used to investigate ammonia transport across the bacteroid and peribacteroid membranes (PBM) from soybean (Glycine max) root nodules. Free-living Bradyrhizobium japonicum USDA110 grown under nitrogen-limited conditions showed rapid MA uptake with saturation kinetics at neutral pH, indicative of a carrier. Exchange of accumulated MA for added ammonia occurred, showing that the carrier recognized both NH(4) (+) and CH(3)NH(3) (+). MA uptake by isolated bacteroids, on the other hand, was very slow at low concentrations of MA and increased linearly with increasing MA concentration up to 1 millimolar. Ammonia did not inhibit MA by isolated bacteroids and did not cause efflux of accumulated MA. PBM-enclosed bacteroids (peribacteroid units [PBUs]) were qualitatively similar to free bacteroids with respect to MA transport. The rates of uptake and efflux of MA by PBUs were linearly dependent on the imposed concentration gradient and unaffected by NH(4)Cl. MA uptake by PBUs increased exponentially with increasing pH, confirming that the rate increased linearly with increasing CH(3)NH(2) concentration. The results are consistent with other evidence that transfer of ammonia from the nitrogen-fixing bacteroid to the host cytosol in soybean root nodules occurs solely by simple diffusion of NH(3) across both the bacteroid and peribacteroid membranes.

Journal Article↗
PubMed1978

Denitrification and ammonia formation in anaerobic coastal sediments.

Simultaneous determinations of nitrogen gas production, ammonia, and particulate organic nitrogen formation in the coastal sediments of Mangoku-Ura, Simoda Bay, and Tokyo Bay were made by using the N-label tracer method. The rate of nitrogen gas production in the sediment surface layer was about 10 mug atom of N per g per h, irrespective of the location of the sediments examined. [N]ammonia and -particulate organic nitrogen accounted for 20 to 70% of the three products, and after several hours of incubation, the major fraction of nondenitrified N in Mangoku-Ura and Simoda Bay sediments was recovered as ammonia. In Tokyo Bay sediments, particulate organic nitrogen was produced at a greater rate than was ammonia. The reduction rate data suggest that the pathway of nitrate reduction to ammonia is important in coastal sediments.

Journal Article↗
PubMed1982

Optimization of Conditions for Photoproduction of Ammonia from Nitrate by Anacystis nidulans.

The effect of several relevant environmental factors influencing the photoproduction of ammonia from nitrate by Anacystis nidulans cells treated with the glutamine synthetase inhibitor l-methionine-dl-sulfoximine has been investigated. The optimal ratio between l-methionine-dl-sulfoximine concentration (micro-molar) and cell density (micrograms of chlorophyll per milliliter) was around 1, the process taking place at maximal rate at a temperature of about 40 degrees C, within the pH range of 7 to 10. Ammonia production was stimulated by CO(2) or bicarbonate and was not affected by the accumulation of ammonia in the medium up to concentrations of 30 mM. The rate of ammonia production was found to be determined by the interaction of at least four factors, namely, irradiance and the density, depth, and turbulence of the cell suspension. Ammonia photoproduction from nitrate and water represents an interesting process for the conversion of light energy into chemical energy, which can operate at high efficiency, around 30% of its theoretical maximum.

Journal Article↗
PubMed1984

Liquid chromatographic-fluorescence determination of ammonia from nitrogenase reactions: a 2-min assay.

The analytical potential of the reaction of ammonia with o-phthalaldehyde mercaptoethanol reagent at pH 7 (an atypical fluorescence) has already been demonstrated. This, coupled with additional findings reported here, has led to an ammonia determination well suited to nitrogenase studies. As a result, large numbers of samples can be rapidly analyzed by high-pressure liquid chromatrography methods under mild conditions and without prior microdiffusion. Neither sodium dithionite (or other components of the usual nitrogenase assay), nor alternative substrates (cyanide, azide, methyl isonitrile), nor their products (methylamine, dimethylamine, hydrazine) interfere. High-pressure liquid chromatography showed that the fluorescent "product" of the o-phthalaldehyde mercaptoethanol reagent-ammonia reaction was, in fact, more than just a single compound. Despite this, once the proper solvent composition was found, high-pressure liquid chromatography with a small inexpensive C(18) "guard" column proved quite fast and reproducible for this measurement. Fluorescence response to ammonia was linear to at least 40 nmol/ml. A previous problem, long-term stability of the fluorescence, was solved by running the reactions in the dark. Background ammonia in the buffer could be substantially reduced by an analogous o-phthalaldehyde mercaptoethanol reagent reaction, using t-butyl mercaptan, and solvent extraction.

Journal Article↗
PubMed1998

Analysis of beta-subgroup proteobacterial ammonia oxidizer populations in soil by denaturing gradient gel electrophoresis analysis and hierarchical phylogenetic probing

A combination of denaturing gradient gel electrophoresis (DGGE) and oligonucleotide probing was used to investigate the influence of soil pH on the compositions of natural populations of autotrophic beta-subgroup proteobacterial ammonia oxidizers. PCR primers specific to this group were used to amplify 16S ribosomal DNA (rDNA) from soils maintained for 36 years at a range of pH values, and PCR products were analyzed by DGGE. Genus- and cluster-specific probes were designed to bind to sequences within the region amplified by these primers. A sequence specific to all beta-subgroup ammonia oxidizers could not be identified, but probes specific for Nitrosospira clusters 1 to 4 and Nitrosomonas clusters 6 and 7 (J. R. Stephen, A. E. McCaig, Z. Smith, J. I. Prosser, and T. M. Embley, Appl. Environ. Microbiol. 62:4147-4154, 1996) were designed. Elution profiles of probes against target sequences and closely related nontarget sequences indicated a requirement for high-stringency hybridization conditions to distinguish between different clusters. DGGE banding patterns suggested the presence of Nitrosomonas cluster 6a and Nitrosospira clusters 2, 3, and 4 in all soil plots, but results were ambiguous because of overlapping banding patterns. Unambiguous band identification of the same clusters was achieved by combined DGGE and probing of blots with the cluster-specific radiolabelled probes. The relative intensities of hybridization signals provided information on the apparent selection of different Nitrosospira genotypes in samples of soil of different pHs. The signal from the Nitrosospira cluster 3 probe decreased significantly, relative to an internal control probe, with decreasing soil pH in the range of 6.6 to 3.9, while Nitrosospira cluster 2 hybridization signals increased with increasing soil acidity. Signals from Nitrosospira cluster 4 were greatest at pH 5.5, decreasing at lower and higher values, while Nitrosomonas cluster 6a signals did not vary significantly with pH. These findings are in agreement with a previous molecular study (J. R. Stephen, A. E. McCaig, Z. Smith, J. I. Prosser, and T. M. Embley, Appl. Environ. Microbiol 62:4147-4154, 1996) of the same sites, which demonstrated the presence of the same four clusters of ammonia oxidizers and indicated that selection might be occurring for clusters 2 and 3 at acid and neutral pHs, respectively. The two studies used different sets of PCR primers for amplification of 16S rDNA sequences from soil, and the similar findings suggest that PCR bias was unlikely to be a significant factor. The present study demonstrates the value of DGGE and probing for rapid analysis of natural soil communities of beta-subgroup proteobacterial ammonia oxidizers, indicates significant pH-associated differences in Nitrosospira populations, and suggests that Nitrosospira cluster 2 may be of significance for ammonia-oxidizing activity in acid soils.

Journal Article↗
PubMed2004

Expression of the ammonia transporter proteins Rh B glycoprotein and Rh C glycoprotein in the intestinal tract.

Ammonia metabolism is important in multiple aspects of gastrointestinal physiology, but the mechanisms of ammonia transport in the gastrointestinal tract remain incompletely defined. The present study examines expression of the ammonia transporter family members Rh B glycoprotein (RhBG) and Rh C glycoprotein (RhCG) in the mouse gastrointestinal tract. Real-time RT-PCR amplification and immunoblot analysis identified mRNA and protein for both RhBG and RhCG were expressed in stomach, duodenum, jejunum, ileum, and colon. Immunohistochemistry showed organ and cell-specific expression of both RhBG and RhCG. In the stomach, both RhBG and RhCG were expressed in the fundus and forestomach, but not in the antrum. In the forestomach, RhBG was expressed by all nucleated squamous epithelial cells, whereas RhCG was expressed only in the stratum germinativum. In the fundus, RhBG and RhCG immunoreactivity was present in zymogenic cells but not in parietal or mucous cells. Furthermore, zymogenic cell RhBG and RhCG expression was polarized, with apical RhCG and basolateral RhBG immunoreactivity. In the duodenum, jejunum, ileum, and colon, RhBG and RhCG immunoreactivity was present in villous, but not in mucous or crypt cells. Similar to the fundic zymogenic cell, RhBG and RhCG expression in villous epithelial cells was polarized when apical RhCG and basolateral RhBG immunoreactivity was present. Thus the ammonia transporting proteins RhBG and RhCG exhibit cell-specific, axially heterogeneous, and polarized expression in the intestinal tract suggesting they function cooperatively to mediate gastrointestinal tract ammonia transport.

Animals↗
PubMed1995

Plasma ammonia concentration in brown trout in soft acidic water and its relationship to decreased swimming performance

Adult brown trout (300­600 g) were acclimated for 2 weeks to an artificial soft water (Ca2+, 50 µmol l-1) and maintained at either 5 °C (October to March) or 15 °C (May to August). Following insertion of a cannula into the dorsal aorta under MS-222 anaesthesia and a recovery period of 2 days, the fish were exposed to a 4 day episode of sub-lethal copper levels at pH 5 or kept at control conditions of pH 7 without copper. The copper concentrations had been predetermined by toxicity testing and were approximately 0.47 µmol l-1 at 5 °C and 0.08 µmol l-1 at 15 °C. At 5 °C, a group of fish was also exposed to approximately 0.08 µmol l-1 copper at pH 5. Plasma total ammonia (Tamm) concentration was significantly elevated by exposure to copper and pH 5. In resting trout exposed to the appropriate sub-lethal copper concentration at pH 5, Tamm was six and 7.5 times greater at 5 and 15 °C, respectively, than those of control trout at the respective temperatures. Although unconfirmed, an elevation of ammonia production alone seems unlikely to account for such substantial increases. From previous studies, there is little evidence of impairment of respiratory gas exchange in trout exposed to these copper concentrations and yet, in the acidic test waters, the gradient of NH3 partial pressure between fish and water was 5.5­6 times greater than that under control conditions. Swimming performance determined by the critical swimming speed (Ucrit) was reduced by copper and acid exposure, and a significant relationship existed between Ucrit and the plasma ammonia concentration of exercised trout. Ammonium ions influence several key enzymes involved in energy metabolism, and elevated ammonia levels might, therefore, reduce the capacity of muscle to exercise. Alternatively, ammonia may have affected the nervous coordination of exercise either centrally or by disrupting peripheral motor innervation.

Journal Article↗
PubMed1999

The marble goby oxyeleotris marmoratus activates hepatic glutamine synthetase and detoxifies ammonia to glutamine during air exposure

Ammonia levels in various tissues of the marble goby Oxyeleotris marmoratus remained constant throughout a 72 h period of air exposure. The rate of ammonia excretion in these experimental fish decreased to approximately one-fifth of that of the submerged control. Ammonia was not converted to urea during air exposure because there were no significant increases in urea content in the tissues. Also, urea excretion rate was lowered to one-fiftieth that of the submerged fish. After 24 h of air exposure, there was a significant increase in muscle glutamine content, which peaked at 48 h. The increase in glutamine content could account for the decreases in the amounts of ammonia and urea excretion during air exposure. The specific activities of hepatic glutamate dehydrogenase (amination) and glutamine synthetase in these experimental fish increased threefold and thirtyfold, respectively, in comparison with the submerged controls. Thus, O. marmoratus appears to be the first known teleost that responds to air exposure by activating hepatic glutamine synthetase to detoxify internally produced ammonia.

Journal Article↗
PubMed2004

Ion chromatographic determination of ammonia in air using a sampling tube of porous carbon.

The ion chromatographic determination of ammonia in air using a sampling tube of porous carbon carbonized at 500 degrees C was examined. When the mean recovery and the reproducibility for a series of five determinations were examined for 1 and 10 ppm ammonia gases, the mean recovery (n = 5) and the relative standard deviation were 97.0% and 3.5% for 1 ppm and 86.9% and 2.8% for 10 ppm, respectively. Furthermore, the recovery from 10 ppm ammonia gas increased with an increase in the extraction time, and a recovery of 99.7% was obtained for 180 min of extraction time. The mean collection efficiency for 1 and 10 ppm ammonia gas was 102.5% and 96.5%, respectively. The relation between the sampling volume and the peak area was linear, and the linearity was 0.999 of the correlation coefficient. The ammonia gas concentration in an actual goat shed could be determined by this sampling device for a sampling volume of 5 L at a flow rate of 1 L/min; 0.79 ppm of the determination value practically agreed as compare with 0.78 ppm from collection by a boric acid solution.

Journal Article↗
PubMed1998

Activity of glutamate dehydrogenase is increased in ammonia-stressed hybridoma cells.

The effect of added ammonia on the intracellular fluxes in hybridoma cells was investigated by metabolic-flux balancing techniques. It was found that, in ammonia-stressed hybridoma cells, the glutamate-dehydrogenase flux is in the reverse direction compared to control cells. This demonstrates that hybridoma cells are able to prevent the accumulation of ammonia by converting ammonia and alpha-ketoglutarate into glutamate. The additional glutamate that is produced by this flux, as compared to the control culture, is converted by the reactions catalyzed by alanine aminotransferase (45% of the extra glutamate) and aspartate aminotransferase (37%), and a small amount is used for the biosynthesis of proline (6%). The remaining 12% of the extra glutamate is secreted into the culture medium. The data suggest that glutamate dehydrogenase is a potential target for metabolic engineering to prevent ammonia accumulation in high-cell-density culture.

Amino Acids↗
PubMed2001

Comparative effects of diet supplementation with l-carnitine and dl-carnitine on ammonia toxicity and hepatic metabolism in rats.

AIM: To compare the effects of chronic supplementation with l-carnitine (LCT) and dl-carnitine (DLC) on ammonia toxicity and hepatic metabolism. METHODS: Three groups of male adult rats were studied: 1) supplemented with LCT (1.2 mmol . kg-1 . d-1), 2) supplemented with DLC (1.2 mmol . kg-1. d-1), and 3) control group (COG) not supplemented. RESULTS: The treatment with LCT decreased the toxicity to ammonia. However, the supplementation with DLC did not show any significant effect. In contrast, the effects of the supplementation with LCT and DLC on hepatic metabolism were quite similar, ie, both groups showed: (a) intensified ammonia uptake and decreased urea production from ammonia; (b) increased glucose and urea production from L-glutamine (5 mmol/L). CONCLUSION: The results suggested that LCT supplementation might protect against ammonia toxicity by extra-hepatic mechanisms.

Acetates↗
PubMed1984

Oxidation of ammonia and hydroxylamine to nitrate in the rat.

We have demonstrated that ammonia is oxidized to nitrate in the rat. Male Sprague-Dawley rats gavaged with 1 000 mumol 15N-ammonium chloride each day for five days were found to excrete low, but significant, amounts of excess 15N-nitrate in their urines on the five days of treatment and on the five subsequent days. We recovered a total of 0.28 +/- 0.03 mumol excess 15N-nitrate (mean +/- SE) per rat, which indicates that ammonia is converted to nitrate with a yield of about 0.0080%. 15N-Hydroxylamine was oxidized in the rat to 15N-nitrate with a yield of 4.7%, but oxidation of 15N-labeled glycine and L-glutamic acid to 15N-nitrate could not be detected. These results suggest that hydroxylamine, but not glycine or L-glutamic acid, may be an intermediate in the ammonia oxidation process. The injection of rats with Arochlor 1254 failed to stimulate nitrate synthesis, which indicates that the cytochrome P-450 drug metabolizing system is probably not involved in ammonia oxidation. Carbon tetrachloride, which causes hepatic lipid peroxidation, produced a small, but significant, increase in nitrate synthesis. Our results are consistent with the hypothesis that ammonia is oxidized in vivo by a non-enzymatic process involving reactive oxygen species. We estimate that a 215 g rat produces 3.0 mumol of nitrate per day by this process. The significance of our results to the problem of endogenous N-nitroso compound formation in man is discussed.

Ammonium Chloride↗
PubMed1998

[Diagnostic value of total plasma levels of bile acids and ammonia in liver diseases in sheep].

For the estimation of the diagnostic value of plasma concentrations of total bile acids and ammonia in liver disease healthy controls (n = 23) as well as animals sick with different diseases were examined. The reference values for total bile acids and ammonia in the plasma of sheep range from 18-166 mumol/l and 15-64 mumol/l, respectively. While animals with chronic copper poisoning (n = 18), vitamin E/selenium deficiency (n = 15) and with diseases not affecting the liver (n = 8) did not show significant differences in concentrations of total bile acids and ammonia from those of the healthy controls, this could be proven for animals with severe hepatopathy or hepatoencephalopathy. Furthermore, some of the latter group showed increased ammonia concentrations in the liquor cerebrospinalis and multifocal vacuolation of the central nervous system. The determination of total bile acids and ammonia in the diagnosis of liver disease in sheep would also be useful. The hepatoencephalic syndrome should therefore be considered as possible differential diagnosis in animals showing neurological signs.

Amino Acids↗
PubMed2004

Role of ammonia in reversal of glutamate-mediated Müller cell swelling in the rat retina.

Glutamate is thought to participate in a variety of retinal degenerative disorders. However, when exposed to glutamate at concentrations up to 1 mM, ex vivo rat retinas typically exhibit Müller cell swelling, but not excitotoxic neuronal damage. This Müller cell swelling is reversible following glutamate washout, indicating that the glial edema is not required for glutamate-induced neuronal injury. It is unclear whether glutamate directly induces the Müller cell swelling or whether a metabolite of glutamate such as glutamine acts as an osmolyte to generate the cellular edema. To examine this issue, ex vivo rat retinas were exposed to 1 mM glutamate or 1 mM glutamine and were evaluated histologically. Glutamate was also combined with 1 mM ammonia or with methionine sulfoximine (MSO), an inhibitor of glutamine synthetase, the enzyme that catalyzes the synthesis of glutamine from glutamate and ammonia. Glutamate-mediated Müller cell swelling was blocked by co-administration of ammonia and the reversibility of Müller cell swelling was inhibited by MSO administered following glutamate exposure. Glutamine alone failed to induce Müller cell swelling. These results indicate that glutamate-mediated Müller cell swelling is unlikely to result from glutamine accumulation. Rather, conversion of glutamate to glutamine in a reaction involving ammonia helps reverse Müller cell swelling following exposure to exogenous glutamate.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1991

Assimilation of ammonia in Paracoccus denitrificans.

Two pathways serve for assimilation of ammonia in Paracoccus denitrificans. Glutamate dehydrogenase (NADP+) catalyzes the assimilation at a high NH4+ concentration. If nitrate serves as the nitrogen source, glutamate is synthesized by glutamate-ammonia ligase and glutamate synthase (NADPH). At a very low NH4+ concentration, all three enzymes are synthesized simultaneously. No direct relationship exists between glutamate dehydrogenase (NADP+) and glutamate-ammonia ligase in P. denitrificans, while the glutamate synthase (NADPH) activity changes in parallel with that of the latter enzyme. Ammonia does not influence the induction or repression of glutamate dehydrogenase (NADP+). The inner concentration of metabolites indicates a possible repression of glutamate dehydrogenase (NADP+) by the high concentration of glutamine or its metabolic products as in the case when NH4+ is formed by assimilative nitrate reduction. No direct effect of the intermediates of nitrate assimilation on the synthesis of glutamate dehydrogenase (NADP+) was observed.

Ammonia↗
PubMed2006

Adenosine diphosphate ribosylation of dinitrogenase reductase and adenylylation of glutamine synthetase control ammonia excretion in ethylenediamine-resistant mutants of Azospirillum brasilense Sp7.

Azospirillum brasilense is a nitrogen-fixing, root-colonizing bacterium that brings about plant-growth-promoting effects mainly because of its ability to produce phytohormones. Ethylenediamine (EDA)-resistant mutants of A. brasilense were isolated and screened for their higher ability to decrease acetylene and release ammonia in the medium. One of the mutants showed considerably higher levels of acetylene decrease and ammonia excretion. Nitrogenase activity of this mutant was relatively resistant to inhibition by NH(4)Cl. Adenosine triphosphate ribosylation of dinitrogenase reductase in the mutant did not increase even in presence of 10 mM NH(4)Cl. Although the mutant showed decreased glutamine synthetase (GS) activity, neither the levels of GS synthesized by the mutant nor the NH (4) (+) -binding site in the GS differed from those of the parent. The main reason for the release of ammonia by the mutant seems to be the fixation of higher levels of nitrogen than its GS can assimilate, as well as higher levels of adenylylation of GS, which may decrease ammonia assimilation.

Adenosine Diphosphate Ribose↗
PubMed1984

Phytoalexin synthesis in soybean cells: elicitor induction of phenylalanine ammonia-lyase and chalcone synthase mRNAs and correlation with phytoalexin accumulation.

A glucan elicitor from cell walls of the fungus Phytophthora megasperma f. sp. glycinea, a pathogen of soybean (Glycine max), induced large and rapid increases in the activities of enzymes of general phenylpropanoid metabolism, phenylalanine ammonia-lyase, and of the flavonoid pathway, acetyl-CoA carboxylase and chalcone synthase, in suspension-cultured soybean cells. The changes in phenylalanine ammonia-lyase and chalcone synthase activities were correlated with corresponding changes in the mRNA activities encoding these enzymes, as determined by enzyme synthesis in vitro in a mRNA-dependent reticulocyte lysate. The time courses of the elicitor-induced changes in mRNA activities for both enzymes were very similar with respect to each other. Following the onset of induction, the two mRNA activities increased significantly at 3 h, reached highest levels at 5 to 7 h, and subsequently returned to low values at 10 h. Similar degrees of induction of mRNA activities and of the catalytic activities of phenylalanine ammonia-lyase and chalcone synthase were observed in response to three diverse microbial compounds, the glucan elicitor from P. megasperma, xanthan, an extracellular polysaccharide from Xanthomonas campestris, and endopolygalacturonase from Aspergillus niger. However, whereas the glucan elicitor induced the accumulation of large amounts of the phytoalexin, glyceollin, in soybean cells, endopolygalacturonase induced only low, albeit significant, amounts; xanthan did not enhance glyceollin accumulation under the conditions of this study. This result might imply that enzymes other than phenylalanine ammonia-lyase or chalcone synthase exert an important regulatory function in phytoalexin synthesis in soybean cells.

Acyltransferases↗
PubMed1978

A specific and reversible macromolecular inhibitor of phenylalanine ammonia-lyase and cinnamic acid-4-hydroxylase in gherkins.

A non-dialysable inhibitor of phenylalanine ammonia-lyase (L-phenylalanine ammonia-lyase, EC 4.3.1.5) has been partially purified from dark-grown gherkin hypocotyls. On extraction of tissue it is found both in the soluble (106 000 X g supernatant) and microsomal (106 000 X g pellet) fractions and can be extracted from the microsomal membranes with 10 mM sodium cholate and 1 M KCl. The soluble and microsomal fractions have similar properties, suggesting the presence of the same active component. The inhibitor is small (Mr less than 20 000), thermolabile, sensitive to proteolytic digestion, and apparently hydrophobic. Purification of the inhibitor was achieved by chromatography on DEAE-cellulose by gel filtration on Sephadex G-50. The inhibitor preparations inhibit phenylalanine ammonia-lyase isolated from a number of plant tissues and also cinnamic acid-4-hydroxylase (trans-cinnamate, NADPH:oxygen oxidoreductase (4-hydroxylating), EC 1.14.13.11) from gherkins and peas, but not a wide range of other enzymes. The evidence suggests that inhibition of the two enzymes is due to the same substance, but this has not yet been confirmed. Kinetic experiments show that the inhibitor is competitive with phenylalanine for the lyase and that its association with the lyase is reversible. Further, a mixture of inhibitor and lyase can be separated on non-denaturing polyacrylamide gels without loss of lyase activity. The activities of phenylalanine ammonia-lyase and cinnamic acid 4-hydroxylase are often concurrently regulated and both have regulatory roles in phenol metabolism; it is suggested that the inhibitor may be specifically involved in controlling their activities in vivo.

Ammonia-Lyases↗