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At least 685 records · Page 38Linked to original sources
PubMed2006

Ammonium recruitment and ammonia transport by E. coli ammonia channel AmtB.

To investigate substrate recruitment and transport across the Escherichia coli Ammonia transporter B (AmtB) protein, we performed molecular dynamics simulations of the AmtB trimer. We have identified residues important in recruitment of ammonium and intraluminal binding sites selective of ammonium, which provide a means of cation selectivity. Our results indicate that A162 guides translocation of an extraluminal ammonium into the pore lumen. We propose a mechanism for transporting the intraluminally recruited proton back to periplasm. Our mechanism conforms to net transport of ammonia and can explain why ammonia conduction is lost upon mutation of the conserved residue D160. We unify previous suggestions of D160 having either a structural or an ammonium binding function. Finally, our simulations show that the channel lumen is hydrated from the cytoplasmic side via the formation of single file water, while the F107/F215 stack at the inner-most part of the periplasmic vestibule constitutes a hydrophobic filter preventing AmtB from conducting water.

Ammonia↗
PubMed1984

Brain methanethiol and ammonia concentrations in experimental hepatic coma and coma induced by injections of various combinations of these substances.

In normal rats in a coma induced by NH+4 alone or by methanethiol alone, the brain and blood levels of ammonia or methanethiol are much higher than those observed in rats in experimental hepatic coma. When various smaller dosage combinations of NH+4, methanethiol, and octanoic acid were injected simultaneously, coma occurred at lower brain and blood concentrations of ammonia and methanethiol. Brain ammonia and methanethiol concentrations in normal rats receiving 0.75 mmol NH+4 plus 0.15 mmol octanoic acid plus 18 mumol methanethiol were comparable with those observed in 24 rats in hepatic coma after fulminant hepatic failure caused by acute massive ischemic liver necrosis. The normal rats became comatose. In these rats and in the rats in hepatic coma, the ammonia level in the brain was increased threefold and the methanethiol level in the brain was increased fivefold. Because these levels of ammonia and methanethiol were sufficient to induce coma in normal rats, they should also have been sufficient to induce coma in rats with damaged livers. Therefore, the accumulation of ammonia and methanethiol in the central nervous system after the acute massive ischemic necrosis may have been sufficient to account for the coma that ensued, without the involvement of other factors.

Ammonia↗
PubMed2002

Production of gaseous nitrogen compounds in a novel process for ammonium removal.

The production of gaseous nitrogen compounds, particularly the greenhouse gas nitrous oxide, was investigated in a novel process for ammonium removal from wastewater. The process is based on the adsorption of ammonium on zeolite followed by bioregeneration. The zeolite serves the dual purpose of an ion exchanger and a physical carrier for nitrifying bacteria which bio-regenerate the ammonium saturated mineral. An analysis of the nitrifying population composition in the reactor fed with simulated secondary effluent (NH4+ = 50 mg/l) revealed that about half of the bacteria in the biofilm were common ammonium oxidizers Nitrosococcus mobilis and Nitrosomonas, while the other half were nitrite oxidizers. The amount of nitrogen losses, under different conditions, and the identification of the emitted gases (N2 or N2O) were investigated in two sets of experiments: (I) batch experiments using biomass originating from the ion exchange reactor with and without the addition of nitrite, and (II) continuous experiments using the ion exchange reactor with zeolite as the biomass carrier. In the batch experiments, nitrite and oxygen concentrations were determined as the major parameters responsible for the formation of gaseous nitrogen gas during ammonia oxidation by autotrophic bacteria. Continuous experiments showed that the major parameter significantly affecting nitrogen losses was the amount of ammonium adsorbed by the zeolite during the ion exchange phase. The amount of ammonium adsorbed determines the ammonium concentration during the initial period of bioregeneration, which in turn directly influences oxygen demand and the resulting concentrations of oxygen and nitrite. It was concluded that the formation of nitrogen gas compounds in the ion exchange/bioregeneration process can be eliminated by adjusting the operational regime to have a shorter adsorption phase resulting in smaller amounts of ammonium adsorbed per cycle.

Adsorption↗
PubMed2003

Renal and hepatic expression of the ammonium transporter proteins, Rh B Glycoprotein and Rh C Glycoprotein.

A family of ammonium transporter proteins was recently identified. Members of this family, Rh B Glycoprotein (RhBG) and Rh C Glycoprotein (RhCG) are expressed in the kidney and the liver, important tissues for ammonium metabolism. Immunohistochemical studies demonstrate basolateral RhBG immunoreactivity in the connecting segment (CNT) and collecting ducts, but not in the proximal tubule or the loop of Henle. Colocalization with thiazide sensitive cotransporter and carbonic anhydrase II confirms expression in the CNT, initial collecting tubule (ICT), and throughout the collecting duct. Colocalization with AE1 and pendrin demonstrates expression is greatest in A-type intercalated cells in the cortical collecting duct (CCD), outer medullary collecting duct (OMCD) and inner medullary collecting duct (IMCD), present in the CCD principal cell, and not detectable in either pendrin-positive CCD intercalated cells or in non-intercalated cells in the OMCD and IMCD. RhCG immunoreactivity has a similar axial distribution as RhBG. However, RhCG immunoreactivity is apical, and is detectable in all CCD and outer stripe of OMCD cells. The liver, a second organ involved in ammonia metabolism, also expresses both RhBG and RhCG. Basolateral RhBG immunoreactivity is present in the perivenous hepatocyte, but is not present in either the periportal or mid-zonal hepatocyte. Hepatic RhCG mRNA is expressed at lower levels than RhBG, and RhCG protein is detected in bile duct epithelium. These findings indicate that RhBG and RhCG are involved in at least two organs that transport ammonia, and that they are located in sites where they are likely to mediate important roles in ammonia transport.

Animals↗
PubMed2004

Nitrous oxide-forming codenitrification catalyzed by cytochrome P450nor.

Intact cells of the denitrifying fungus Fusarium oxysporum were previously shown to catalyze codenitrification to form a hybrid nitrous oxide (N2O) species from nitrite and other nitrogen compounds such as azide and ammonia. Here we show that cytochrome P450nor can catalyze the codenitrification reaction to form N2O from nitric oxide (NO) but not nitrite, and azide or ammonia. The results show that the direct substrate of the codenitrification by intact cells should not be nitrite but NO, which is formed from nitrite by the reaction of a dissimilatory nitrite reductase.

Anaerobiosis↗
PubMed1977

Micro-electrode measurement of the intracellular pH and buffering power of mouse soleus muscle fibres.

1. The intracellular pH (pHi) of surface fibres of the mouse soleus muscle has been measured in vitro using recessed-tip pH-sensitive microelectrodes. 2. In 5% CO2 and pH 7-40, the mean pHi was 7-07 +/- 0-007 (S.E. of mean) at 37 degrees C and 7-23 +/- 0-01 at 28 degrees C. The difference between these tow values is the same as the change in neutral pH between 37 and 28 degrees C. 3. Alteration of the CO2 level at constant external pH caused a biphasic change in pHi with a rapid displacement followed by a slower partial recovery. Because the recovery was incomplete, different stable pHi values were recorded at different CO2 levels, the higher the CO2 the lower the pHi. The differences in pHi were highly significant both at 37 and 28 degrees C. 4. Alteration of the CO2 level at constant external pH also changed the membrane potential (Em), an increase in CO2 leading to an increased Em. The dependence of Em on the CO2 level was much smaller in the fast-twitch muscle, extensor digitorum longus, than in soleus. 5. Changing external pH, either by alteration of the bicarbonate or CO2 level of the Ringer solution, caused pHi to change by a mean 38-7% of the external pH change. The change in pHi was accomplished about 10 times more rapidly, and in the same direction, by altering CO2 than by altering the bicarbonate. 6. Application of external NH3 and NH+4 caused a rapid intracellular alkalinization followed by a slower acidification. On removal of external NH3 and NH+4, there was a large and rapid acdification, followed by a fairly rapid recovery in pHi. 7. The size of the pHi changes occurring on alteration of the CO2 level at both constant external pH and constant external bicarbonate, and on removal of external NH3 and NH+4, suggests a non-CO2 buffering power of 45m-equiv H+ ions/pH unit per litre and a constant-CO2 buffering power of 58 m-equiv H+ ions/pH unit per litre. The buffering power was apparently unaffected by a change in temperature between 37 and 28 degrees C. 8. It was concluded that H+ ions are not passively distributed across the muscle cell membrane, and that the pHi is closely controlled by the active transport of H+, OH- or HCO-3 ions.

Ammonia↗
PubMed1982

Ammonium action on post-synaptic inhibition in crayfish neurones: implications for the mechanism of chloride extrusion.

1. The reversal potential of the Cl(-)-dependent, inhibitory post-synaptic potential (E(i.p.s.p.)) was measured in the isolated crayfish stretch receptor neurone using two intracellular micro-electrodes. The difference between E(i.p.s.p.) and the resting membrane potential (E(m)), the i.p.s.p. driving force, was reversibly decreased by addition of NH(3)/NH(4) (+), and the mechanism of this decrease was investigated.2. The NH(3)/NH(4) (+)-induced decrease in i.p.s.p. driving force was dose-dependent with an onset at about 0.2 mM. E(i.p.s.p.) always remained more negative than E(m) or, when the neurone was spontaneously firing, the threshold potential. E(m) and resting membrane resistance (R(m)) also decreased in a dose-dependent fashion. Synaptic conductance (g(s)) increased with low doses, but decreased on application of 20 mM-NH(3)/NH(4) (+). All the effects were fully reversible on return to normal Ringer solution.3. Intracellular acidification (substitution of 50% Cl(-) by acetate compared with isethionate) considerably reduced the i.p.s.p. driving force. Simultaneous application of NH(3)/NH(4) (+) and acetate-substituted Ringer solution caused a similar decrease in the driving force to application of the same concentration of NH(3)/NH(4) (+) under normal conditions. Increasing the extracellular pH at which a given concentration of NH(3)/NH(4) (+) was applied caused a smaller decline in the i.p.s.p. driving force. These results suggest that intracellular acidification decreases the i.p.s.p. driving force and that the NH(3)/NH(4) (+)-induced decline is caused by an action of the ammonium ion.4. Elevation of extracellular K(+) (K(+) (0)) decreased the i.p.s.p. driving force, E(m) and R(m), and increased g(s). Reduction of K(+) (0) had the converse effects on all parameters.5. Application of Rb(+) or Cs(+) mimicked the effects of NH(3)/NH(4) (+). Substitution of K(+) (0) by Rb(+), Cs(+) or NH(3)/NH(4) (+) opposed or even reversed the increase in i.p.s.p. driving force when Na(+) was used as the substitute. The effectiveness of the various cations in decreasing the driving force was in the following order: Rb(+) > NH(4) (+) > K(+) > Cs(+).6. Inhibition of the Na pump by ouabain or K(+)-free Ringer solution caused a gradual reduction in the i.p.s.p. driving force. Since the driving force also decreased when the Na(+) gradient probably was increased (elevated K(+) (0)), this suggests a dependence on the K(+) gradient rather than the Na(+) gradient or the Na pump itself.7. Frusemide (6 x 10(-4) M) reversibly decreased the i.p.s.p. driving force and E(m), and increased g(s). R(m) was not significantly affected. Application of frusemide in the presence of 5 mM-Rb(+) and vice versa, caused a further reduction in the driving force. The recovery of the driving force on removal of either agent was slowed by the presence of the other.8. Application of 4,4-diisothiocyanostilbene-2,2-disulphonic acid (DIDS; 10(-4) M) caused spontaneous firing and reduced E(i.p.s.p.) to the threshold potential. R(m) and g(s) increased. The effects were slowly reversible on removal of the drug.9. It is proposed that the i.p.s.p. driving force is maintained by a K(+)-Cl(-) co-transport mechanism, driven by the K(+) gradient. The K(+) site exhibits the binding selectivity: Rb(+) > NH(4) (+) > K(+) > Cs(+) and the mechanism is inhibited partially by frusemide and completely by DIDS.

Acetates↗
PubMed2005

Nitrogen removal from piggery waste using the combined SHARON and ANAMMOX process.

Nitrogen removal in piggery waste was investigated with the combined SHARON-ANAMMOX process. The piggery waste was characterized as strong nitrogenous wastewater with very low C/N ratio. For the preceding SHARON reactor, ammonium nitrogen loading and conversion rates were 0.97 kg NH4-N/m3 reactor/day and 0.73 kg NH4-N/m3 reactor/day, respectively. Alkalinity consumption for ammonium conversion was 8.5 gr bicarbonate utilized per gram ammonium nitrogen converted to NO2-N or NO3-N at steady-states operation. The successive ANAMMOX reactor was fed with the effluent from SHARON reactor. Nitrogen loading and conversion rates were 1.36 kg soluble N/m3 reactor/day and 0.72 kg soluble N/m3 reactor/day, respectively. The average NO2-N/NH4-N removal ratio by ANAMMOX reaction was 2.13. It has been observed that Candidatus "Kuenenia stuttgartiensis" were dominated in the ANAMMOX reactor based on FISH analysis.

Aerobiosis↗
PubMed2000

[The balance of harmful trace contaminants between the air humidity condensate and air in a simulator of the Mir orbit station moisture condensation unit].

Subject of the investigation was the balance of harmful trace contaminants (HTC) between the air moisture condensate and air in a simulator of the MIR moisture condensation unit. Experiments involved various classes of water-solvent compounds including alcohols (C1-C4), ketons (C1-C2), aldehydes (C1-C2), fatty acids (C2-C4), esters (acetates C4-C6), and ammonium. For most of the compounds, removal efficiency correlates with air humidity and virtually does not depend on the HTC concentration within the range of 0.25 to 59.1 mg/m3.

Acetates↗
PubMed2001

Sensitivity of particulate matter nitrate formation to precursor emissions in the California San Joaquin Valley.

The formation of secondary ammonium nitrate during the 1995 Integrated Monitoring Study (IMS95) in San Joaquin Valley, CA was investigated using a box model that simulates the atmospheric chemistry and gas/particle partition of inorganic compounds. The concentration of particulate matter (PM) nitrate was found to be sensitive to reductions in VOC emissions. Nitric acid, rather than ammonia, was the limiting reagent in the formation of PM nitrate. The formation of nitric acid was more sensitive to the availability of oxidants than that of NOx. Oxidant chemistry in wintertime conditions in the San Joaquin Valley was shown to be VOC-sensitive. In fact, a decrease in NOx emissions may have the counter-intuitive effect of increasing PM nitrate.

Air Pollutants↗