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PubMed1997

Effect of ammonia on motor function in adult rats.

Changes in motor function were assessed in male rats after injecting graded doses (100, 200, 400, and 800 mg/kg, IP) of ammonium chloride and ammonium acetate. The effects were correlated with the concentrations of ammonia and glucose in the brain and blood. Spontaneous motor activity and motor coordination were inhibited after injecting 100 and 200 mg/kg, whereas with 400 and 800 mg/kg the animals exhibited convulsive movements. A dose-dependent increase was found in the concentrations of ammonia and glucose in both blood and brain. These were restored, 25 min after treatment, to control levels in the blood and not in the brain. A correlation was found between the time courses of inhibitory motor events and a rise in brain ammonia levels. Convulsant action of ammonium salts was accompanied by a marked elevation of ammonia and glucose concentration in the brain. The findings suggest that detoxication of diffused ammonia is a rate-limiting process in the brain and that ammonia, at toxic concentrations, decreases glucose utilization in the brain, resulting in an inhibition of motor function. A very high concentration of ammonia in the brain, although inhibiting glucose utilization, produces clonic convulsions probably by activating directly the motor neurons.

Acetates↗
PubMed2002

Ammonia-induced extracellular accumulation of taurine in the rat striatum in vivo: role of ionotropic glutamate receptors.

Accumulation of taurine (Tau), glutamate (Glu) and glutamine (Gln) was measured in vivo in microdialysates of the rat striatum following a direct application to the microdialysis tube of 60 mM ammonium chloride which renders the final ammonia concentration in the extracellular space to approximately 5 mM. The following compounds were coadministered with ammonia to distinguish between the different mechanisms that may underlie the accumulation of amino acids: ion transport inhibitors, diisothiocyanostilbene-2,2'-disulfonate (DIDS) and furosemide, a Glu transport inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (PDC), an NMDA receptor antagonist dizocilpine (MK-801) and an 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate (KA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). Ammonia stimulated Tau accumulation in the microdialysates to approximately 250% of the basal value. Furosemide did not significantly affect the stimulation by ammonia and DIDS only moderately depressed the effect. The ammonia-dependent Tau accumulation was increased by approximately 50% in the presence of PDC and reduced by approximately 35% in the presence dizocilpine and DNQX. In the microdialysates ammonia stimulated Glu and Gln accumulation somewhat less than Tau accumulation. Except for stimulation of Gln accumulation by DNQX, the effects were not modified by any of the cotreatments. The results are consistent with the assumption that ammonia stimulates Tau efflux mainly via activation of ionotropic Glu receptors.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2006

Electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) surfaces.

The electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) has been studied using voltammetry, chronoamperometry, and in situ infrared spectroscopy. The oxidative adsorption of ammonia results in the formation of NH(x) (x = 0-2) adsorbates. On Pt(111), ammonia oxidation occurs in the double-layer region and results in the formation of NH and, possibly, N adsorbates. The experimental current transients show a hyperbolic decay (t(-1)), which indicates strong lateral (repulsive) interactions between the (reacting) species. On Pt(100), the NH(2) adsorbed species is the stable intermediate of ammonia oxidation. Stabilization of the NH and NH(2) fragments on Pt(111) and Pt(100), respectively, is in an interesting agreement with recent theoretical predictions. The Pt(111) surface shows extremely low activity in ammonia oxidation to dinitrogen, thus indicating that neither NH nor N (strongly) adsorbed species are active in dinitrogen production. Neither nitrous oxide nor nitric oxide is the product of ammonia oxidation on Pt(111) at potentials up to 0.9 V, as deduced from the in situ infrared spectroscopy measurements. The Pt(100) surface is highly active in dinitrogen production. This process is characterized by a Tafel slope of 30 mV decade(-1), which is explained by a rate-determining dimerization of NH(2) fragments followed by a fast decay of the resulting surface-bound hydrazine to dinitrogen. Therefore, the high activity of the Pt(100) surface for ammonia oxidation to dinitrogen is likely to be related to its ability to stabilize the NH(2) adsorbate.

Journal Article↗
PubMed1969

Induction of phenylalanine ammonia-lyase in Xanthium leaf disks. Photosynthetic requirement and effect of daylength.

A cycloheximide-sensitive increase in the activity of phenylalanine ammonia-lyase (EC 4.3.1.5) occurs in Xanthium leaf disks exposed to light. Radioactive ammonia-lyase has been isolated by means of sucrose density gradient centrifugation and starch gel electrophoresis from disks fed l-isoleucine-U-(14)C or l-arginine-U-(14)C. The incorporation of radioactive amino acids into phenylalanine ammonia-lyase together with the inhibitory effects of cycloheximide indicate that the observed increase in enzyme activity involves the induction of lyase synthesis.The light-dependent synthesis of the ammonia-lyase is completely inhibited by 50 mum 3-(4-chlorophenyl)-1,1-dimethylurea (CMU) indicating that photosynthesis is involved. Only a trace quantity of some photosynthetic product must be needed because half light saturation occurs at very low intensity (ca. 30 ft-c). Exogenous carbohydrate is also required for continuing enzyme synthesis over a 72 hr period. But carbohydrate does not replace the photosynthetic requirement in darkness. Enzyme formed in light disappears rapidly from disks placed in the dark. The decay of ammonia-lyase activity follows first order kinetics. The half-life of the lyase ranged from 6 to 15 hr in leaf material used. Cyoloheximide inhibits the decay of lyase activity. Thus the maintenance of turnover in Xanthium leaf disks requires de novo synthesis of protein. That turnover, i.e., degradation as well as synthesis of lyase protein occurs is suggested by the apparent loss of radioactive ammonia-lyase from leaf disks placed in darkness. Light-induced synthesis coupled with rapid turnover can produce a diurnal fluctuation of ammonia-lyase activity in Xanthium leaf disks. Alternating periods of enzyme synthesis and degradation were observed in disks exposed to 24 hr cycles of light and dark. The average level of enzyme activity maintained in the tissue was directly related to the length of the light period. Induction of lyase synthesis was also observed in excised leaves and to a lesser extent in leaves of whole plants.

Carbon Isotopes↗
PubMed1971

The induction of phenylalanine ammonia lyase and phaseollin by 9-aminoacridine and other deoxyribonucleic Acid intercalating compounds.

Bean pod tissue (Phaseolus vulgaris L. var. Top Crop) is induced to produce phaseollin when challenged with various microorganisms. The pods react in the same manner when challenged with 9-aminoacridine. This compound also caused an increase in concentrations of phenylalanine ammonia lyase, an enzyme of the phaseollin synthesizing pathway. Both the synthesis of phenylalanine ammonia lyase and phaseollin are subject to inhibition by actinomycin D, cycloheximide, or 6-methylpurine. The results suggest that both phaseollin production and increased phenylalanine ammonia lyase, when induced by 9-aminoacridine, require newly synthesized RNA and protein.The concentration of 9-aminoacridine optimal for synthesis of phaseollin and PAL (0.5 mg/ml) does not increase the rate of total protein synthesis. However, there is a differential effect of 9-aminoacridine on synthesis of certain protein fractions. Optimal concentrations of 9-aminoacridine induce phaseollin and phenylalanine ammonia lyase synthesis while reducing the net synthesis of RNA during the period of induction.The planar three-ring structure of 9-aminoacridine appears to be a desirable feature for phaseollin and phenylalanine ammonia lyase induction. Similar compounds, all DNA intercalators, having dimethylamino, diethylamino, amino, or 9-alkylamino substitutions of a three-ring acridine skeleton, are also inducers of phenylalanine ammonia lyase and phaseollin synthesis.It is suggested that 9-aminoacridine and other DNA intercalators function as inducers of phaseollin and phenylalanine ammonia lyase synthesis by reacting with the DNA template.

Journal Article↗
PubMed1977

Polarographic study of ammonia assimilation by isolated chloroplasts.

Illuminated pea (Pisum sativum) chloroplasts catalyze (ammonia plus alpha-ketoglutarate [alpha-KG])-dependent O(2) evolution at rates which are commensurate with other estimates of the flux of assimilated nitrogen (mean of eight determinations, 8.3 mumole per mg chlorophyll per hour, sd 2.4). The reaction was usually initiated with 1 mm ammonia after preincubating chloroplasts in the presence of alpha-KG, ADP, pyrophosphate, and MgCl(2).Progressive increases in ammonia concentration gave V(max)/2 at 0.2 mm (approximately) and V(max) at about 1 mm. Higher concentrations were inhibitory; at 7 mm the rate was again about V(max)/2. The highest ratio of O(2) evolved per mol of ammonia supplied was 0.36.The (ammonia plus alpha-KG)-dependent reaction was inhibited by methionine sulfoximine, azaserine, and aspartate in the presence of amino-oxyacetate but not by amino-oxyacetate alone and not by l-glutamate. The rate of O(2) evolution in the presence of 1 mm ammonia and 2.5 mm alpha-KG was increased only slightly by addition of 5 mm glutamine. Similarly, the rate of O(2) evolution in the presence of 5 mm glutamine and 2.5 mm alpha-KG was increased only slightly by addition of 1 mm ammonia.The results are attributed to the incorporation of ammonia via glutamine synthetase and reductive transamination of the glutamine formed by photosynthetically coupled glutamate synthase using alpha-KG as the amino acceptor. Several lines of evidence rule out the possibility that photosynthetically coupled glutamate dehydrogenase is involved.

Journal Article↗
PubMed1984

Sustained Photoproduction of Ammonia from Dinitrogen and Water by the Nitrogen-Fixing Cyanobacterium Anabaena sp. Strain ATCC 33047.

Conditions have been developed that lengthen the time during which photosynthetic dinitrogen fixation by filaments of the cyanobacterium Anabaena sp. strain ATCC 33047 proceeds freely, whereas the subsequent conversion of ammonia into organic nitrogen remains blocked, with the resulting ammonia released to the outer medium. When l-methionine-dl-sulfoximine was added every 20 h, maximal rates of ammonia production (25 to 30 mumol/mg of chlorophyll per h) were maintained for about 50 h. After this time, ammonia production ceased due to a deficiency of glutamine and other nitrogenous compounds in the filaments, conditions which finally led to cell lysis. The effective ammonia production period could be further extended to about 7 days by adding a small amount of glutamine at the end of a 40-h production period or by allowing the cells to recover for 8 h in the absence of l-methionine-dl-sulfoximine after every 40-h period in the presence of the inhibitor. A more prolonged steady production of ammonia, lasting for longer than 2 weeks, was achieved by alternating treatments with the glutamine synthetase inhibitors l-methionine-dl-sulfoximine and phosphinothricin, provided that 8-h recovery periods in the absence of either compound were also alternated throughout. The biochemically manipulated cyanobacterial filaments thus represent a system that is relatively stable with time for the conversion of light energy into chemical energy, with the net generation of a valuable fuel and fertilizer through the photoreduction of dinitrogen to ammonia.

Journal Article↗
PubMed1996

Dynamics of nitrification and denitrification in root-oxygenated sediments and adaptation of ammonia-oxidizing bacteria to low-oxygen or anoxic habitats.

Oxygen-releasing plants may provide aerobic niches in anoxic sediments and soils for ammonia-oxidizing bacteria. The oxygen-releasing, aerenchymatous emergent macrophyte Glyceria maxima had a strong positive effect on numbers and activities of the nitrifying bacteria in its root zone in spring and early summer. The stimulation of the aerobic nitrifying bacteria in the freshwater sediment, ascribed to oxygen release by the roots of G. maxima, disappeared in late summer. Numbers and activities of the nitrifying bacteria were positively correlated, and a positive relationship with denitrification activities also was found. To assess possible adaptations of ammonia-oxidizing bacteria to low-oxygen or anoxic habitats, a comparison was made between the freshwater lake sediment and three soils differing in oxicity profiles. Oxygen kinetics and tolerance to anoxia of the ammonia-oxidizing communities from these habitats were determined. The apparent K(infm) values for oxygen of the ammonia-oxidizing community in the lake sediment were in the range of 5 to 15 (mu)M, which was substantially lower than the range of K(infm) values for oxygen of the ammonia-oxidizing community from a permanently oxic dune location. Upon anoxic incubation, the ammonia-oxidizing communities of dune, chalk grassland, and calcareous grassland soils lost 99, 95, and 92% of their initial nitrifying capacity, respectively. In contrast, the ammonia-oxidizing community in the lake sediment started to nitrify within 1 h upon exposure to oxygen at the level of the initial capacity. It is argued that the conservation of the nitrifying capacity during anoxic periods and the ability to react instantaneously to the presence of oxygen are important traits of nitrifiers in fluctuating oxic-anoxic environments such as the root zone of aerenchymatous plant species.

Journal Article↗
PubMed2002

Synergistic effects of dust and ammonia on the occupational health effects of poultry production workers.

OBJECTIVE: As production methods for livestock and poultry moved towards large industrial-scale confinement facilities, the occupational health community reported risks for respiratory illnesses in workers. Likely, greater risks for respiratory disease will occur with the continuing trend towards full-time confinement workers, who inspire a combination of bioaerosols, particulates, and gases. Although there have been numerous studies on the individual health effects of air contaminants inside confined animal production facilities, there have been no reports on the effects of combined exposures. The objective of this study was to investigate the combined health effects of air contaminants on poultry production workers. SAMPLE POPULATION: Two hundred and fifty-seven poultry production workers participated in this study. The workers represented various areas of the poultry industry, including turkey growing, broiler production, egg laying, and unloading/shakeling in poultry processing. Worker procedures pulmonary function testing was conducted before and after a four-hour work shift. The work environment was assessed for total and respirable dust, ammonia, endotoxin and CO2. The relationship of simultaneous total dust and ammonia exposures was examined by correlation, logistic modeling, and synergy index calculations. RESULTS: Synergy between ammonia levels and airborne dust explained up to 43% and 63% of the decline (respectively for Forced Expiratory Volume (FEV) in one second and Forced Expiratory Flow (FEF25-75) in pulmonary function over the work shift. Furthermore, assessing the synergy index indicated the combined effect of dust and ammonia is from 53 to 156% (greater combined than individually). The proportion of health effect due to synergy is 35%-61%. CONCLUSIONS: Synergy of simultaneous dust and ammonia exposures in a working environment raises the question of redefining exposure limits for organic dust and ammonia when workers are exposed simultaneously to these substances. CLINICAL RELEVANCE: Control of both dust and ammonia in livestock facilities is extremely important. Lack of control of both these contaminants will increase the risk of respiratory dysfunction to all exposed to this environment, including workers and veterinarians.

Journal Article↗
PubMed1992

14C2H2- and 14CO2-labeling studies of the de novo synthesis of polypeptides by Nitrosomonas europaea during recovery from acetylene and light inactivation of ammonia monooxygenase.

Incubation of cells of the nitrifying bacterium Nitrosomonas europaea with 14C2H2 results in the covalent attachment of 14C label to a membrane-bound polypeptide of an approximate Mr of 28,000 (Hyman, M.R., and Wood, P.M. (1985) Biochem. J. 227, 719-725). A labeling procedure using 14C2H2 generated from Ba14CO3 has been used to investigate the correlation between the extent of covalent modification of this polypeptide by 14C from 14C2H2 and the level of ammonia oxidizing activity in whole cells. The time-dependent inactivation of ammonia monooxygenase by 14C2H2 resulted in a progressive and saturable incorporation of 14C into a 27-kDa polypeptide. In contrast, the specific, time-dependent and complete inactivation of ammonia monooxygenase by light resulted in concomitant decrease in the ability of cells to incorporate 14C from 14C2H2 into this polypeptide. The 14C2H2 labeling procedure was also used to investigate the recovery of ammonia monooxygenase activity after complete inactivation of pre-existing ammonia monooxygenase by either C2H2 or light. The recovery of ammonia monooxygenase activity was closely correlated with a recovery of ability of cells to incorporate 14C label from 14C2H2 into the 27-kDa polypeptide. This recovery process was energy (NH4+)-dependent and was inhibited by chloramphenicol and rifampicin, implying that de novo protein synthesis was required. Additional polypeptides labeled with 14C from 14CO2 were also identified during recovery from C2H2 or light inactivation of ammonia monooxygenase.

Acetylene↗
PubMed1977

Ammonia assimilation in the fission yeast Schizosaccharomyces pombe 972.

Glutamine synthetase (GS) activity of Schizosaccharomyces pombe 972 was high in ammonia-limited cultures, low in phosphate- and sulphate-limited cultures and not detected in glucose-limited cultures. When ammonia was 'pulsed' into an ammonia-limited culture then GS activity decreased at a rate faster than that calculated if enzyme synthesis ceased and enzyme was diluted out by growth. Enzyme activity increased in ammonia-starved, phosphate-limited cultures and in the ammonia 'pulse' system when the added ammonia had been utilised. These increases in enzyme activity were prevented by the presence of 100 mug/ml cycloheximide. GS activity was inversely related to the intracellular concentration of glutamate.

Ammonia↗
PubMed1989

Ammonia causes a drop in intracellular pH in metabolizing cortical brain slices. A [31P]- and [1H]nuclear magnetic resonance study.

[31P]- and [1H]Nuclear magnetic resonance spectroscopy were used to study metabolism in cortical brain slices in the guinea-pig during acute exposure to pathophysiological concentrations of ammonia. Intracellular acidification, measured from the chemical shift of endogenous inorganic phosphate, was observed without any change in cellular energy status or concentrations of lactate, glutamate and glutamine. The initial acidification, which developed over a period of 9 min appeared to be heterogeneous, on the basis of a splitting of the inorganic phosphate resonance in a number of experiments, corresponding to pH changes of 0.07 and 0.27 pH units. Subsequently a homogeneous acidification, of 0.15 pH units, developed by 23 min following exposure to ammonia. Intracellular pH recovered within 6 min after discontinuation of the ammonia load. In the absence of external bicarbonate, intracellular pH was 0.12 units more acidic than in the bicarbonate buffer and ammonia caused a further acidification by 0.16 units. When glutamine synthase inhibitor, methionine sulphoximine, was added, there was a slow fall in intracellular pH. Under these conditions, subsequent addition of ammonia failed to cause acidification directly. Thus acute elevation of ammonia does not lead to a change in cerebral high-energy phosphate or lactate metabolism, but may be associated with a fall in cortical intracellular pH.

Acid-Base Equilibrium↗
PubMed2005

Expression of ornithine-urea cycle enzymes in early life stages of air-breathing walking catfish Clarias batrachus and induction of ureogenesis under hyper-ammonia stress.

The air-breathing walking catfish Clarias batrachus is a potential ureogenic teleost with having a full complement of ornithine-urea cycle (OUC) enzymes expressed in various tissues. The present study was aimed at determining the pattern of nitrogenous waste excretion in the form of ammonia-N and urea-N along with the changes of tissue ammonia and urea levels, and the expression of OUC enzymes and glutamine synthetase (GSase) in early life stages of this teleost, and further, to study the possible induction of ureogenesis in 15-day old fry under hyper-ammonia stress. The ammonia and urea excretion was visible within 12 h post-fertilization (hpf), which increased several-fold until the yolk was completely absorbed by the embryo. Although all the early developing stages were primarily ammoniotelic, they also excreted significant amount of nitrogen (N) in the form of urea-N (about 35-40% of total N). Tissue levels of ammonia and urea also increased along with subsequent developmental stages at least until the yolk absorption stage. All the OUC enzymes and GSase were expressed within 4-12 hpf showing an increasing trend of activity for all the enzymes until 350 hpf. There was a significant increase of activity of GSase, carbamyl phosphate synthetase III (CPSase III) and argininosuccinate lyase enzymes (ASL), accompanied with significant increase of enzyme protein concentration of at least two enzymes (GSase and CPSase III) in the 15-day old fry following exposure to 10 mM NH4Cl as compared to respective controls kept in water over a period of 72 h. Thus, it appears that the OUC enzymes are expressed in early life stages of walking catfish like other teleosts, but at relatively high levels and remain expressed all through the life stages with a potential of stimulation of ureogenesis throughout the life cycle as a sort of physiological adaptation to survive and breed successfully under hyper-ammonia and various other environmental-related stresses.

Air↗
PubMed1985

Functional hepatocyte heterogeneity in ammonia metabolism. The intercellular glutamine cycle.

In the rat liver acinus area synthesis and glutaminase activity are predominantly localized in the periportal area, whereas glutamine synthetase activity and the transport system for glutamate in the plasma membrane are perivenous. Detoxification of ammonium ions at low concentrations occurs exclusively by glutamine synthesis, but not by urea formation. Therefore, the two pathways of ammonia detoxification in the liver acinus represent the sequence of a low-affinity, but high-capacity system (urea synthesis) and a high-affinity system (glutamine synthesis). In agreement with this finding, obtained in experiments with the metabolically- and structurally-intact perfused rat liver, is also an almost complete inhibition of perivenous glutamine synthesis without impairment of periportal urea synthesis. This was shown after induction of a perivenous liver cell necrosis following CCl4 pretreatment with the consequence of a diminished hepatic ammonia extraction. Periportal glutaminase and perivenous glutamine synthetase are simultaneously active, resulting in an intercellular (as opposed to intracellular) glutamine cycle, being under the control of hormones, pH and portal ammonia and glutamine concentrations. The intercellular glutamine cycle provides an effective means for almost complete conversion of portal ammonium ions to urea by additional substrate supply of periportal urea synthesis, by periportal glutamine degradation and by the perivenous re-synthesis of glutamine from ammonia which escaped urea synthesis. Because urea synthesis, in contrast to glutamine synthesis, is a major pathway for the removal of bicarbonate, the switching of ammonia detoxification from urea synthesis to glutamine synthesis in acidosis or vice versa in alkalosis points to an important role of the liver in maintaining pH homeostasis. The acid-base-induced changes of the route of hepatic ammonia detoxification and therefore bicarbonate removal are performed by the regulatory properties of the enzymes of the intercellular glutamine cycle.

Acid-Base Equilibrium↗
PubMed1965

THE REDUCTION OF NITRATE, NITRITE AND HYDROXYLAMINE TO AMMONIA BY ENZYMES FROM CUCURBITA PEPO L. IN THE PRESENCE OF REDUCED BENZYL VIOLOGEN AS ELECTRON DONOR.

1. Enzyme systems from Cucurbita pepo have been shown to catalyse the reduction of nitrite and hydroxylamine to ammonia in yields about 90-100%. 2. Reduced benzyl viologen serves as an efficient electron donor for both systems. Activity of the nitrite-reductase system is directly related to degree of dye reduction when expressed in terms of the function for oxidation-reduction potentials, but appears to decrease to negligible activity below about 9% dye reduction. 3. NADH and NADPH alone produce negligible nitrite loss, but NADPH can be linked to an endogenous diaphorase system to reduce nitrite to ammonia in the presence of catalytic amounts of benzyl viologen. 4. The NADH- or NADPH-nitrate-reductase system that is also present can accept electrons from reduced benzyl viologen, but shows relationships opposite to that for the nitrite-reductase system with regard to effect of degree of dye reduction on activity. The product of nitrate reduction may be nitrite alone, or nitrite and ammonia, or ammonia alone, according only to the degree of dye reduction. 5. The relative activities of nitrite-reductase and hydroxylamine-reductase systems show different relationships with degree of dye reduction and may become reversed in magnitude when effects of degree of dye reduction are tested over a suitable range. 6. Nitrite severely inhibits the rate of reduction of hydroxylamine without affecting the yield of ammonia as a percentage of total substrate loss, but hydroxylamine has a negligible effect on the activity of the nitrite-reductase system. 7. The apparent K(m) for nitrite (1 mum) is substantially less than that for hydroxylamine, for which variable values between 0.05 and 0.9mm (mean 0.51 mm) have been observed. 8. The apparent K(m) values for reduced benzyl viologen differ for the nitrite-reductase and hydroxylamine-reductase systems: 60 and 7.5 mum respectively. 9. It is concluded that free hydroxylamine may not be an intermediate in the reduction of nitrite to ammonia by plants, and a possible mechanism for reduction of both compounds by the same enzyme system is discussed in the light of current ideas relating to other organisms.

Ammonia↗
PubMed1965

EFFECTS OF DIELDRIN, PICROTOXIN AND TELODRIN ON THE METABOLISM OF AMMONIA IN BRAIN.

1. Increases in the concentrations of lactic acid and pyruvic acid in rat brain during acute dieldrin poisoning are associated with hyperactivity of the brain, whereas an increase in the cerebral alanine concentration occurs before the convulsions. Throughout the dieldrin-induced seizure pattern, fluctuations in the concentration of brain ammonia are out of phase with the actual convulsions. 2. Increases in the concentrations of alanine, ammonia and lactic acid in rat brain accompany picrotoxin-induced seizures; there is no increase in the concentration of glutamine. These changes are consistent with the inhibition of glutamine synthesis. 3. In addition to previously reported changes in the concentrations of intermediary metabolites of the brain after the administration of Telodrin (Hathway & Mallinson, 1964), increases have now been found in the alanine and lactic acid concentrations. Since increases in the alanine and glutamine concentrations occur before the convulsions, liberation of ammonia also occurs before the onset of convulsions and throughout their course. Ammonia-binding mechanisms later become inadequate and free ammonia accumulates in cerebral tissues. 4. An increase in the pyruvic acid concentration of the brain after the intraperitoneal injection of either dieldrin or Telodrin is endogenous in origin. 5. The parenteral administration of a small dose of glutamine increases the cerebral concentrations of alanine and glutamic acid. Some animals previously treated with glutamine resisted Telodrin convulsions. 6. Mechanisms for the disposal of ammonia liberated in brain are discussed.

Alanine↗
PubMed2026

Hypoosmolarity inhibits ammonia oxidation by terrestrial and freshwater Nitrosopumilaceae members.

Salinity strongly influences the physiology and distribution of nitrifying microorganisms, yet the effects of low salinity remain understudied. This study investigates the impact of hypoosmolarity on different groups of ammonia oxidizers in soil and freshwater reservoirs, as well as in pure culture isolates. In soil microcosms amended with ammonium, at low salinity levels (~120 μS/cm), comparable to values commonly found in pristine terrestrial and freshwater environments, the abundance of ammonia-oxidizing bacteria (AOB), dominated by Nitrosomonas oligotropha, significantly increased. In contrast, the growth of ammonia-oxidizing archaea (AOA), dominated by "Candidatus Nitrosotenuis" of the Nitrosopumilaceae family, was stimulated by high salinity (~760 μS/cm). In ammonium-fed freshwater microcosms, the abundance of AOB, dominated by N. oligotropha, significantly increased under both low (~170 μS/cm) and high salinity (~850 μS/cm) conditions. In the presence of allylthiourea (50 μM), used to inhibit bacterial ammonia oxidation, AOA were sensitive to low salinity in both soil and freshwater microcosms. Consistently, culture-dependent studies revealed marked growth inhibition of terrestrial AOA, especially members of Nitrosopumilaceae, under hypoosmolarity, unlike AOB and complete ammonia oxidizer (comammox) strains. Genomic analyses, along with transcriptomic studies, suggested that the sensitivity of AOA to hypoosmolarity stress was possibly due to a lack of osmoregulatory transport systems and their S-layer cell wall structure. Overall, this study indicates hypoosmolarity as an important factor shaping the ecological niches and distribution of ammonia oxidizers, as well as nitrification activities, in terrestrial and freshwater environments that are increasingly affected by intensified water cycles due to global change.

Ammonia↗
PubMed1975

Ammonia assimilation by rhizobium cultures and bacteroids.

The enzymes involved in the assimilation of ammonia by free-living cultures of Rhizobium spp. are glutamine synthetase (EC. 6.o.I.2), glutamate synthase (L-glutamine:2-oxoglutarate amino transferase) and glutamate dehydrogenase (ED I.4.I.4). Under conditions of ammonia or nitrate limitation in a chemostat the assimilation of ammonia by cultures of R. leguminosarum, R. trifolii and R. japonicum proceeded via glutamine synthetase and glutamate synthase. Under glucose limitation and with an excess of inorganic nitrogen, ammonia was assimilated via glutamate dehydrogenase, neither glutamine synthetase nor glutamate synthase activities being detected in extracts. The coenzyme specificity of glutamate synthase varied according to species, being linked to NADP for the fast-growing R. leguminosarum, R. melitoti, R. phaseoli and R. trifolii but to NAD for the slow-growing R. japonicum and R. lupini. Glutamine synthetase, glutamate synthase and glutamate dehydrogenase activities were assayed in sonicated bacteroid preparations and in the nodule supernatants of Glycine max, Vicia faba, Pisum sativum, Lupinus luteus, Medicago sativa, Phaseolus coccineus and P. vulgaris nodules. All bacteroid preparations, except those from M. sativa and P. coccineus, contained glutamate synthase but substantial activities were found only in Glycine max and Lupinus luteus. The glutamine synthetase activities of bacteroids were low, although high activities were found in all the nodule supernatants. Glutamate dehydrogenase activity was present in all bacteroid samples examined. There was no evidence for the operation of the glutamine synthetase/glutamate synthase system in ammonia assimilation in root nodules, suggesting that ammonia produced by nitrogen fixation in the bacteroid is assimilated by enzymes of the plant system.

Acetylene↗