Permeation of ammonia across bilayer lipid membranes studied by ammonium ion selective microelectrodes

Antonenko, Yuri N.; Pohl, Peter; Denisov, G.A.

doi:10.1016/s0006-3495(97)78862-3

Cited by 80 publications

(82 citation statements)

References 20 publications

(31 reference statements)

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“…Bilayer tightening by cholesterol and sphingomyelin decreases the diffusivity of small molecules, thereby increasing membrane resistance. For example, bilayer tightening decreases membrane permeability to water by up to tenfold (31,32) and to ammonia by threefold (24). However, cholesterol-and sphingomyelincontaining bilayers had the same H 2 S permeability of P M Ն 0.5 cm/s (Fig.…”

Section: Resultsmentioning

confidence: 92%

“…Although there is little doubt that they facilitate the membrane transport of NH 3 (18), the contribution of aquaporins to NO, CO 2 , or O 2 transport is under debate (19)(20)(21)(22)(23). At the same time as the permeability of P M,CO 2 ϭ 3.2 cm/s allows CO 2 to pass membranes freely (22), the NH 3 permeability P M,NH 3 ϭ 0.016 cm/s (24) indicates that a cholesterol-containing epithelial membrane acts as a barrier and, consequently, that membrane channels (aquaporin-8) facilitate NH 3 diffusion (18). The different findings for NH 3 and CO 2 are in agreement with Overton's rule (25,26) which, based on the biphasic partition coefficients (Table 1) predicts the large difference in P M .…”

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confidence: 99%

See 1 more Smart Citation

No facilitator required for membrane transport of hydrogen sulfide

Mathai

Missner²,

Kügler

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

325

226

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Hydrogen sulfide (H2S) has emerged as a new and important member in the group of gaseous signaling molecules. However, the molecular transport mechanism has not yet been identified. Because of structural similarities with H 2O, it was hypothesized that aquaporins may facilitate H 2S transport across cell membranes. We tested this hypothesis by reconstituting the archeal aquaporin AfAQP from sulfide reducing bacteria Archaeoglobus fulgidus into planar membranes and by monitoring the resulting facilitation of osmotic water flow and H2S flux. To measure H2O and H2S fluxes, respectively, sodium ion dilution and buffer acidification by proton release (H 2S % H ؉ ؉ HS ؊ ) were recorded in the immediate membrane vicinity. Both sodium ion concentration and pH were measured by scanning ion-selective microelectrodes. A lower limit of lipid bilayer permeability to H 2S, P M,H 2 S > 0.5 ؎ 0.4 cm/s was calculated by numerically solving the complete system of differential reaction diffusion equations and fitting the theoretical pH distribution to experimental pH profiles. Even though reconstitution of AfAQP significantly increased water permeability through planar lipid bilayers, PM,H 2 S remained unchanged. These results indicate that lipid membranes may well act as a barrier to water transport although they do not oppose a significant resistance to H 2S diffusion. The fact that cholesterol and sphingomyelin reconstitution did not turn these membranes into an H2S barrier indicates that H 2S transport through epithelial barriers, endothelial barriers, and membrane rafts also occurs by simple diffusion and does not require facilitation by membrane channels. aquaporins ͉ gas transport ͉ membrane permeability ͉ unstirred layer ͉ signaling

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Section: Resultsmentioning

confidence: 92%

mentioning

confidence: 99%

No facilitator required for membrane transport of hydrogen sulfide

Mathai

Missner²,

Kügler

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

325

226

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“…Because membrane tightening by cholesterol and SM does not reduce membrane CO 2 permeability below 3.2 cm/s, facilitation of CO 2 membrane transport by proteinaceous molecules is virtually impossible. Here, CO 2 transport differs fundamentally from ammonia and water transport, which, in the absence of specific membrane channels, exhibit permeabilities that are orders of magnitude smaller (2,9,22).…”

Section: Discussionmentioning

confidence: 98%

“…Analytical Model-Similar to our previous weak acid/base transport model (9,17), all relevant proton-transfer reactions and diffusion processes were taken into account. Using Fick's 1st and 2nd laws, a set of coupled differential Equations 2 and 3 was written, where J i cis , c i cis , J i trans , and c i trans are, respectively, the fluxes and the concentrations of the ith species in the membrane vicinity in the cis and trans compartments.…”

mentioning

confidence: 99%

Carbon Dioxide Transport through Membranes

Missner

Kügler

Saparov

et al. 2008

Journal of Biological Chemistry

151

212

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Several membrane channels, like aquaporin-1 (AQP1) and the RhAG protein of the rhesus complex, were hypothesized to be of physiological relevance for CO 2 transport. However, the underlying assumption that the lipid matrix imposes a significant barrier to CO 2 diffusion was never confirmed experimentally. Here we have monitored transmembrane CO 2 flux (J CO2 ) by imposing a CO 2 concentration gradient across planar lipid bilayers and detecting the resulting small pH shift in the immediate membrane vicinity. An analytical model, which accounts for the presence of both carbonic anhydrase and buffer molecules, was fitted to the experimental pH profiles using inverse problems techniques. At pH 7.4, the model revealed that J CO2 was entirely rate-limited by near-membrane unstirred layers (USL), which act as diffusional barriers in series with the membrane. Membrane tightening by sphingomyelin and cholesterol did not alter J CO2 confirming that membrane resistance was comparatively small. In contrast, a pH-induced shift of the CO 2 hydration-dehydration equilibrium resulted in a relative membrane contribution of about 15% to the total resistance (pH 9.6). Under these conditions, a membrane CO 2 permeability (3.2 ؎ 1.6 cm/s) was estimated. It indicates that cellular CO 2 uptake (pH 7.4) is always USL-limited, because the USL size always exceeds 1 m. Consequently, facilitation of CO 2 transport by AQP1, RhAG, or any other protein is highly unlikely. The conclusion was confirmed by the observation that CO 2 permeability of epithelial cell monolayers was always the same whether AQP1 was overexpressed in both the apical and basolateral membranes or not.The widely accepted model that gases like NH 3 , CO 2 , and O 2 pass biological membranes by diffusion through the lipid matrix has been recently called into question. For example, the membrane protein channels AmtB and aquaporin-8 have been identified to transport NH 3 (1, 2). Protein channels such as the human aquaporin-1, the plant aquaporin NtAQP1, and the RhAG protein of the rhesus complex were reported to provide a pathway for CO 2 transport (3-5). The similarity in the findings for NH 3 and CO 2 is very surprising because Overtone's rule predicts that their permeabilities, P M , across the lipid phase of biological membranes differ 750-fold. The number was calculated assuming that NH 3 and CO 2 have comparable membrane diffusivities and that neither one of them belongs to those extremely rare exceptions from Overtone's rule (6, 7) so that the proportionality between P M and the biphasic partition coefficient (water/organic solvent) applies as shown in Equation 1,where K CO2 ϳ 1.5 (8), K NH3 ϳ 0.002 (6), and P M,NH3 ϭ 0.016 cm/s (9).A P M , CO2 of 12 cm/s suggests that the lipid matrix of biological membranes cannot act as a barrier to CO 2 diffusion. In fact, a stagnant water layer adjacent to the membrane that has the same thickness (␦) as the membrane would generate the same resistance to CO 2 flow as is caused by the membrane itself. Because these so-called unstirr...

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“…These equilibrium ratios are dependent on the pH difference between compartments (e.g., pH Cyt (6). This illustrates that the maximum flux over the membrane could be more than five times higher than the N uptake rate (0.226 mmol/g CDW /h) ( Table 1) and shows that the cytosol/vacuole equilibrium assumption is realistic due to the potentially high NH 3 diffusion rate between the compartments.…”

Section: Nhmentioning

confidence: 87%

In Vivo Analysis of NH ₄ ⁺ Transport and Central Nitrogen Metabolism in Saccharomyces cerevisiae during Aerobic Nitrogen-Limited Growth

Cueto-Rojas

Seifar

Pierick

et al. 2016

Appl Environ Microbiol

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Ammonium is the most common N source for yeast fermentations. Although its transport and assimilation mechanisms are well documented, there have been only a few attempts to measure the in vivo intracellular concentration of ammonium and assess its impact on gene expression. Using an isotope dilution mass spectrometry (IDMS)-based method, we were able to measure the intracellular ammonium concentration in N-limited aerobic chemostat cultivations using three different N sources (ammonium, urea, and glutamate) at the same growth rate (0.05 h ؊1 ). The experimental results suggest that, at this growth rate, a similar concentration of intracellular (IC) ammonium, about 3.6 mmol NH 4 ؉ /liter IC , is required to supply the reactions in the central N metabolism, independent of the N source. Based on the experimental results and different assumptions, the vacuolar and cytosolic ammonium concentrations were estimated. Furthermore, we identified a futile cycle caused by NH 3 leakage into the extracellular space, which can cost up to 30% of the ATP production of the cell under N-limited conditions, and a futile redox cycle between Gdh1 and Gdh2 reactions. Finally, using shotgun proteomics with protein expression determined relative to a labeled reference, differences between the various environmental conditions were identified and correlated with previously identified N compound-sensing mechanisms. IMPORTANCEIn our work, we studied central N metabolism using quantitative approaches. First, intracellular ammonium was measured under different N sources. The results suggest that Saccharomyces cerevisiae cells maintain a constant NH 4 ؉ concentration (around 3 mmol NH 4 ؉ /liter IC ), independent of the applied nitrogen source. We hypothesize that this amount of intracellular ammonium is required to obtain sufficient thermodynamic driving force. Furthermore, our calculations based on thermodynamic analysis of the transport mechanisms of ammonium suggest that ammonium is not equally distributed, indicating a high degree of compartmentalization in the vacuole. Additionally, metabolomic analysis results were used to calculate the thermodynamic driving forces in the central N metabolism reactions, revealing that the main reactions in the central N metabolism are far from equilibrium. Using proteomics approaches, we were able to identify major changes, not only in N metabolism, but also in C metabolism and regulation. Saccharomyces cerevisiae is a versatile organism that can grow on a large variety of N sources, namely, ammonium (NH 4 ϩ ), urea, citrulline, ornithine, gamma aminobutyric acid (GABA), allatoin, allantoate, and all proteinogenic L-amino acids, with the exceptions of L-lysine, L-histidine, and L-cysteine (1, 2). Therefore, S. cerevisiae cells require complex machinery to achieve metabolic regulation for efficient uptake and anabolic and catabolic processing of N compounds.In particular, S. cerevisiae can differentiate between preferred and nonpreferred N sources using the nitrogen catabolite repression (NCR) pa...

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Permeation of ammonia across bilayer lipid membranes studied by ammonium ion selective microelectrodes

Cited by 80 publications

References 20 publications

No facilitator required for membrane transport of hydrogen sulfide

No facilitator required for membrane transport of hydrogen sulfide

Carbon Dioxide Transport through Membranes

In Vivo Analysis of NH ₄ ⁺ Transport and Central Nitrogen Metabolism in Saccharomyces cerevisiae during Aerobic Nitrogen-Limited Growth

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Permeation of ammonia across bilayer lipid membranes studied by ammonium ion selective microelectrodes

Cited by 80 publications

References 20 publications

No facilitator required for membrane transport of hydrogen sulfide

No facilitator required for membrane transport of hydrogen sulfide

Carbon Dioxide Transport through Membranes

In Vivo Analysis of NH 4 + Transport and Central Nitrogen Metabolism in Saccharomyces cerevisiae during Aerobic Nitrogen-Limited Growth

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In Vivo Analysis of NH ₄ ⁺ Transport and Central Nitrogen Metabolism in Saccharomyces cerevisiae during Aerobic Nitrogen-Limited Growth