Articoli di riviste: "Membrane d’échangeuse de protons"

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Sokolov, Valerij S., Vsevolod Yu Tashkin, Darya D. Zykova, Yulia V. Kharitonova, Timur R. Galimzyanov e Oleg V. Batishchev. "Electrostatic Potentials Caused by the Release of Protons from Photoactivated Compound Sodium 2-Methoxy-5-nitrophenyl Sulfate at the Surface of Bilayer Lipid Membrane". Membranes 13, n. 8 (8 agosto 2023): 722. http://dx.doi.org/10.3390/membranes13080722.

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Lateral transport and release of protons at the water–membrane interface play crucial roles in cell bioenergetics. Therefore, versatile techniques need to be developed for investigating as well as clarifying the main features of these processes at the molecular level. Here, we experimentally measured the kinetics of binding of protons released from the photoactivated compound sodium 2-methoxy-5-nitrophenyl sulfate (MNPS) at the surface of a bilayer lipid membrane (BLM). We developed a theoretical model of this process describing the damage of MNPS coupled with the release of the protons at the membrane surface, as well as the exchange of MNPS molecules and protons between the membrane and solution. We found that the total change in the boundary potential difference across the membrane, ∆ϕb, is the sum of opposing effects of adsorption of MNPS anions and release of protons at the membrane–water interface. Steady-state change in the ∆ϕb due to protons decreased with the concentration of the buffer and increased with the pH of the solution. The change in the concentration of protons evaluated from measurements of ∆ϕb was close to that in the unstirred water layer near the BLM. This result, as well as rate constants of the proton exchange between the membrane and the bulk solution, indicated that the rate-limiting step of the proton surface to bulk release is the change in the concentration of protons in the unstirred layer. This means that the protons released from MNPS remain in equilibrium between the BLM surface and an adjacent water layer.

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Ababneh, Omar, Abdallah Barjas Qaswal, Ahmad Alelaumi, Lubna Khreesha, Mujahed Almomani, Majdi Khrais, Oweiss Khrais et al. "Proton Quantum Tunneling: Influence and Relevance to Acidosis-Induced Cardiac Arrhythmias/Cardiac Arrest". Pathophysiology 28, n. 3 (3 settembre 2021): 400–436. http://dx.doi.org/10.3390/pathophysiology28030027.

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Acidosis and its associated pathologies predispose patients to develop cardiac arrhythmias and even cardiac arrest. These arrhythmias are assumed to be the result of membrane depolarization, however, the exact mechanism of depolarization during acidosis is not well defined. In our study, the model of quantum tunneling of protons is used to explain the membrane depolarization that occurs during acidosis. It is found that protons can tunnel through closed activation and inactivation gates of voltage-gated sodium channels Nav1.5 that are present in the membrane of cardiac cells. The quantum tunneling of protons results in quantum conductance, which is evaluated to assess its effect on membrane potential. The quantum conductance of extracellular protons is higher than that of intracellular protons. This predicts an inward quantum current of protons through the closed sodium channels. Additionally, the values of quantum conductance are influential and can depolarize the membrane potential according to the quantum version of the GHK equation. The quantum mechanism of depolarization is distinct from other mechanisms because the quantum model suggests that protons can directly depolarize the membrane potential, and not only through indirect effects as proposed by other mechanisms in the literature. Understanding the pathophysiology of arrhythmias mediated by depolarization during acidosis is crucial to treat and control them and to improve the overall clinical outcomes of patients.

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Weichselbaum, Ewald, e Peter Pohl. "Protons at the membrane water interface". Biochimica et Biophysica Acta (BBA) - Bioenergetics 1859 (settembre 2018): e117. http://dx.doi.org/10.1016/j.bbabio.2018.09.346.

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Rayabharam, Archith, e N. R. Aluru. "Quantum water desalination: Water generation through separate pathways for protons and hydroxide ions in membranes". Journal of Applied Physics 132, n. 19 (21 novembre 2022): 194302. http://dx.doi.org/10.1063/5.0122324.

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Much of the water desalination strategies has focused on designing pores and membranes that transport water and reject ions and other molecules at a high rate. In this paper, we discuss an approach where protons (H+) and hydroxide (OH−) ions are transported via different mechanisms through a porous membrane, and subsequently, once they have been transported through the membrane, they recombine to generate water. 2D materials such as graphene and MoS2 have generated significant interest for applications such as desalination. Here, we explore the applicability of one such 2D material—a cubic Ti2C MXene membrane—in desalination by creating a OH− ion selective pore, which significantly suppresses protons but allows OH− ions and water to go through. The catalytic properties of MXenes enable the dissociation of water on the surface, and the dissociated protons translocate through the membrane via quantum-dominated phenomena such as hopping from interstitial-to-interstitial. OH− ions translocate through a positively charged pore and recombine with protons on the other side of the membrane to form water. Our results indicate that water molecules generated via quantum processes can significantly enhance the overall transport of water across the membrane.

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Bramhall, John. "Conductance routes for protons across membrane barriers". Biochemistry 26, n. 10 (maggio 1987): 2848–55. http://dx.doi.org/10.1021/bi00384a028.

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Abdallat, Mahmoud, Abdallah Barjas Qaswal, Majed Eftaiha, Abdel Rahman Qamar, Qusai Alnajjar, Rawand Sallam, Lara Kollab et al. "A mathematical modeling of the mitochondrial proton leak via quantum tunneling". AIMS Biophysics 11, n. 2 (2024): 189–233. http://dx.doi.org/10.3934/biophy.2024012.

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<abstract> The mitochondrion is a vital intracellular organelle that is responsible for ATP production. It utilizes both the concentration gradient and the electrical potential of the inner mitochondrial membrane to drive the flow of protons from the intermembrane space to the matrix to generate ATP via ATP-synthase. However, the proton leak flow, which is mediated via the inner mitochondrial membrane and uncoupling proteins, can reduce the efficiency of ATP production. Protons can exhibit a quantum behavior within biological systems. However, the investigation of the quantum behavior of protons within the mitochondria is lacking particularly in the contribution to the proton leak. In the present study, we proposed a mathematical model of protons tunneling through the inner mitochondrial membrane and the mitochondrial carrier superfamily MCF including uncoupling proteins UCPs and the adenine nucleotide translocases ANTs. According to the model and its assumptions, the quantum tunneling of protons may contribute significantly to the proton leak if it is compared with the classical flow of protons. The quantum tunneling proton leak may depolarize the membrane potential, hence it may contribute to the physiological regulation of ATP synthesis and reactive oxygen species ROS production. In addition to that, the mathematical model of proton tunneling suggested that the proton-tunneling leak may depolarize the membrane potential to values beyond the physiological needs which in turn can harm the mitochondria and the cells. Moreover, we argued that the quantum proton leak might be more energetically favorable if it is compared with the classical proton leak. This may give the advantage for quantum tunneling of protons to occur since less energy is required to contribute significantly to the proton leak compared with the classical proton flow. </abstract>

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Keller, David, Seema Singh, Paola Turina, Roderick Capaldi e Carlos Bustamante. "Structure of ATP synthase by SFM and single-particle image analysis". Proceedings, annual meeting, Electron Microscopy Society of America 53 (13 agosto 1995): 722–23. http://dx.doi.org/10.1017/s0424820100139986.

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F1Fo ATP synthases are the proteins responsible for the synthesis of ATP in oxidative phosphorylation, and are present in some form in all aerobic organisms, both prokaryotic and eukaryotic. They use the energy stored in a transmembrane proton gradient (which is generated by other members of the oxidative phosphorylation pathway) to synthesize ATP from ADP and Pi or, working in reverse, to pump protons across the membrane using the energy of ATP hydrolysis. The full protein has two sectors, F1 and Fo. F1 is normally bound to Fo (which is membrane integrated), but is water soluble when dissociated. The F1 sector contains the sites which bind ADP and catalyze its conversion to ATP. The Fo sector contains a channel which allows protons to to cross the membrane, dissipating the transmembrane chemical potential. By an unknown mechanism this translocation of protons through Fo is coupled to the hydrolysis or synthesis of ATP in F1, so that the energy released in hydrolysis of ATP can drive the motion of protons against an electrochemical potential, or the energy of translocating protons can be used to form high energy ADP-Pi bonds.

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M., Ambaga, Tumen-Ulzii A. e Buyantushig T. "THE BUFFERING CAPACITY OF ERYTHROCYTE MEMBRANE SURROUNDINGS IN RELATION TO FREE PROTONS INSIGHTOF NEW ELUCIDATION OF EIGTH AND NINTH STAGES OF THE MEMBRANE REDOXY POTENTIAL THREE STATE DEPENDENT 9 STEPPED FULL CYCLE OF PROTON CONDUCTANCE IN THE HUMAN BODY". International Journal of Advanced Research 10, n. 11 (30 novembre 2022): 29–33. http://dx.doi.org/10.21474/ijar01/15638.

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It was became clear that the flow-fate of all many many protons,generated in mitochondria of 50-80 trillion cells (now by us mitochondria flow of protons named as 1-7 stages of proton conductance) have been needed another special structures - another system needs to soak up the extra H+ activity generated as a result of process conducted in the 1-7 stages of proton conductance in order for true buffering to occur, that system consists of intracellular proteins, of which haemoglobin is the key player, concretely speaking,one of these are the erythrocyte membrane surroundings for packaging of protons and alsoHydrochloric acid formationby Gastric parietal cells,also H+/Na antiport in the membrane transports H+ out of cell and Na ion in the level of Peritubular capillary-Interstitial fluid-Tubule epithelial cells-Tubular fluid with accompanying maintaining of serum and cell pH-7,4.By our suggestion, the buffering capacity of erythrocyte membrane surroundings in relation to free protons, formed in the proton conductance have implemented within Ninth stage -located in the Respiratory membrane, Pulmonary circuit, where occurred oxygen uptake from alveolar air under effect of increased bicarbonate entry by bicarbonate/chloride ion shift mechanism, leading to increase of HbO2 formation, resulting to release of proton,electron from food substrates under the undirect action of oxygen released from membrane surroundings of erythrocyte in the 8-th stage of proton conductance.

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Kluka, Ľubomír, Ernest Šturdík, Štefan Baláž, Dušan Kordík, Michal Rosenberg, Marián Antalík e Jozef Augustín. "Membrane proton transport mediated by phenylhydrazonopropanedinitriles". Collection of Czechoslovak Chemical Communications 53, n. 1 (1988): 186–97. http://dx.doi.org/10.1135/cccc19880186.

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Some fundamental physicochemical characteristics as stability in solutions, solubility in various solvents and association constants describing equilibria with protons and potassium ions in aqueous solutions were determined for phenylhydrazonopropanedinitriles (PHPD). The effect of pH and sodium, potassium, calcium, and magnesium cations on the distribution of PHPD were examined in a two-compartment system 1-octanol-water. The transmembrane transfer of protons by PHPD causing a disturbance of the pH-gradient was verified in vitro using a model three-compartment system water-octanol-water, imitating the in vivo intracristal space-inner mitochondrial membrane – matrix system. Transfer of H+ ions mediated by PHPD in the system under study was found to be considerably faster when an exchange with K+ ions (ion-exchanging antiport H+/K+) was possible. A model was described indicating the reality of ion-exchanging antiport H+/Me+ mediated by PHPD on biomembranes which is in line with the chemiosmotic theory.

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Vidilaseris, Keni, Juho Kellosalo e Adrian Goldman. "A high-throughput method for orthophosphate determination of thermostable membrane-bound pyrophosphatase activity". Analytical Methods 10, n. 6 (2018): 646–51. http://dx.doi.org/10.1039/c7ay02558k.

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Membrane-bound pyrophosphatases (mPPases) are homodimeric integral membrane proteins that hydrolyse pyrophosphate into orthophosphates coupled to the active transport of protons or sodium ions across membranes.

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Ardalan, Afshan, Matthew D. Smith e Masoud Jelokhani-Niaraki. "Uncoupling Proteins and Regulated Proton Leak in Mitochondria". International Journal of Molecular Sciences 23, n. 3 (28 gennaio 2022): 1528. http://dx.doi.org/10.3390/ijms23031528.

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Higher concentration of protons in the mitochondrial intermembrane space compared to the matrix results in an electrochemical potential causing the back flux of protons to the matrix. This proton transport can take place through ATP synthase complex (leading to formation of ATP) or can occur via proton transporters of the mitochondrial carrier superfamily and/or membrane lipids. Some mitochondrial proton transporters, such as uncoupling proteins (UCPs), transport protons as their general regulating function; while others are symporters or antiporters, which use the proton gradient as a driving force to co-transport other substrates across the mitochondrial inner membrane (such as phosphate carrier, a symporter; or aspartate/glutamate transporter, an antiporter). Passage (or leakage) of protons across the inner membrane to matrix from any route other than ATP synthase negatively impacts ATP synthesis. The focus of this review is on regulated proton transport by UCPs. Recent findings on the structure and function of UCPs, and the related research methodologies, are also critically reviewed. Due to structural similarity of members of the mitochondrial carrier superfamily, several of the known structural features are potentially expandable to all members. Overall, this report provides a brief, yet comprehensive, overview of the current knowledge in the field.

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Frank, Pinar, Bernhard Siebenhofer, Theresa Hanzer, Andreas F. Geiss, Florian Schadauer, Ciril Reiner-Rozman, Bill Durham et al. "Proteo-lipobeads for the oriented encapsulation of membrane proteins". Soft Matter 11, n. 15 (2015): 2906–8. http://dx.doi.org/10.1039/c4sm02646b.

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Chistyakov, V. A., Yu O. Smirnova e I. Alperovich. "Feasibility of the C60 Fullerene Antioxidant Properties: Study with Density Functional Theory Computer Modeling". International Journal of Mathematics and Computers in Simulation 15 (27 novembre 2021): 107–9. http://dx.doi.org/10.46300/9102.2021.15.20.

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Fullerene C60 compound was recently found to be a potent anti-oxidant, which may be envisioned as a result of alteration of the inner mitohondria membrane electric potential with protons transport boosted by fullerenes. Here we briefly report on the theoretical test of the very possibility of protons to pass through the surface of C60 fullerene to become confined within latter thus possibly decreasing the transmembrane electric field gradient when fullerene crosses the mitochondria membrane. Quantumchemical calculations within Density Functional Theory are employed as a means of checking described scenario

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JUNGE, WOLFGANG. "Protons, the Thylakoid Membrane, and the Chloroplast ATP Synthase". Annals of the New York Academy of Sciences 574, n. 1 Bicarbonate, (dicembre 1989): 268–86. http://dx.doi.org/10.1111/j.1749-6632.1989.tb25164.x.

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Brzezinski, Peter, Joachim Reimann e Pia Ädelroth. "Molecular architecture of the proton diode of cytochrome c oxidase". Biochemical Society Transactions 36, n. 6 (19 novembre 2008): 1169–74. http://dx.doi.org/10.1042/bst0361169.

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CytcO (cytochrome c oxidase) is a membrane-bound multisubunit protein which catalyses the reduction of O2 to H2O. The reaction is arranged topographically so that the electrons and protons are taken from opposite sides of the membrane and, in addition, it is also linked to proton pumping across the membrane. Thus the CytcO moves an equivalent of two positive charges across the membrane per electron transferred to O2. Proton transfer through CytcO must be controlled by the protein to prevent leaks, which would dissipate the proton electrochemical gradient that is maintained across the membrane. The molecular mechanism by which the protein controls the unidirectionality of proton-transfer (cf. proton diode) reactions and energetically links electron transfer to proton translocation is not known. This short review summarizes selected results from studies aimed at understanding this mechanism, and we discuss a possible mechanistic principle utilized by the oxidase to pump protons.

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DeCoursey, Thomas E. "Voltage and pH sensing by the voltage-gated proton channel, H V 1". Journal of The Royal Society Interface 15, n. 141 (aprile 2018): 20180108. http://dx.doi.org/10.1098/rsif.2018.0108.

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Voltage-gated proton channels are unique ion channels, membrane proteins that allow protons but no other ions to cross cell membranes. They are found in diverse species, from unicellular marine life to humans. In all cells, their function requires that they open and conduct current only under certain conditions, typically when the electrochemical gradient for protons is outwards. Consequently, these proteins behave like rectifiers, conducting protons out of cells. Their activity has electrical consequences and also changes the pH on both sides of the membrane. Here we summarize what is known about the way these proteins sense the membrane potential and the pH inside and outside the cell. Currently, it is hypothesized that membrane potential is sensed by permanently charged arginines (with very high p K a ) within the protein, which results in parts of the protein moving to produce a conduction pathway. The mechanism of pH sensing appears to involve titratable side chains of particular amino acids. For this purpose their p K a needs to be within the operational pH range. We propose a ‘counter-charge’ model for pH sensing in which electrostatic interactions within the protein are selectively disrupted by protonation of internally or externally accessible groups.

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Porter, R. K., e M. D. Brand. "Mitochondrial proton conductance and H+/0 ratio are independent of electron transport rate in isolated hepatocytes". Biochemical Journal 310, n. 2 (1 settembre 1995): 379–82. http://dx.doi.org/10.1042/bj3100379.

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In this paper we examine the non-linearity of the relationship between the proton electrochemical gradient across the mitochondrial inner membrane (delta p) and oxygen consumption of non-phosphorylating mitochondria in situ in hepatocytes. Models proposing to explain the non-linear relationship were tested experimentally. It was shown that the mitochondrial proton conductance and the number of protons pumped to the cytosolic side of the mitochondrial inner membrane by the electron transport complexes per oxygen atom consumed (H+/O ratio) are independent of electron transport rate in mitochondria in isolated hepatocytes. The non-linearity of the plot of delta p against the non-phosphorylating oxygen consumption is due to either a potential-dependent slippage of the proton pumps of the mitochondrial inner membrane and/or a potential-dependent leakage of protons back across the mitochondrial inner membrane.

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Rayabharam, Archith, e N. R. Aluru. "Interstitial proton transport through defective MXenes". Applied Physics Letters 120, n. 21 (23 maggio 2022): 211601. http://dx.doi.org/10.1063/5.0098709.

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Proton transport across nanometer-thick membranes in an aqueous medium is important for applications in energy and molecular sieving. Recently, Hu et al. [Nature 516(7530), 227–230 (2014)] experimentally demonstrated proton tunneling through 2D materials like graphene and hexagonal boron nitride, opening up a wide range of applications in hydrogen-based technologies such as fuel cells. Here, we demonstrate proton transport in an aqueous medium across a 2D cubic Ti2C membrane, a representative defective MXene, from ab initio molecular dynamics simulations. We observe bidirectional translocation of protons, which occurs through the interstitial vacancies in the surface. We show from our simulations that water dissociates on the membrane and the dissociated proton moves into the interstitial sites in the membrane. The proton hops from interstitial-to-interstitial and transports across the membrane. We also show that this interstitial proton transport is associated with an induced electric field that is modulated with bidirectional transport of protons across the membrane.

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Lande, M. B., N. A. Priver e M. L. Zeidel. "Determinants of apical membrane permeabilities of barrier epithelia". American Journal of Physiology-Cell Physiology 267, n. 2 (1 agosto 1994): C367—C374. http://dx.doi.org/10.1152/ajpcell.1994.267.2.c367.

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Renal collecting duct and thick ascending limb, as well as stomach, exhibit strikingly low permeabilities to water and solutes. However, the apical membrane characteristics responsible for these unique permeabilities remain unknown. While the lipid composition of artificial membranes governs membrane permeability, exoplasmic and cytoplasmic leaflets of biological apical membranes exhibit striking asymmetries in lipid composition. This asymmetry, as well as the presence of membrane proteins, may be critical to barrier function. To determine the role of bulk lipid composition in apical membrane barrier function, we compared permeabilities to water (Pf), protons, ammonia, and several small nonelectrolytes of gastric apical membrane vesicles [native gastric vesicles (NGV)] and liposomes prepared from lipids quantitatively extracted from these vesicles [gastric lipid large unilamellar vesicles (LUV)]. Permeabilities were measured on a stopped-flow fluorimeter by monitoring self- or pH-sensitive quenching of entrapped carboxyfluorescein. NGV exhibited low Pf (2.8 +/- 0.3 x 10(-4) cm/s) while gastric lipid LUV Pf averaged 1.2 +/- 0.1 x 10(-3) cm/s, a fourfold increase compared with the value in NGV. Gastric lipid LUV also demonstrated higher permeabilities to protons, ammonia, propylene glycol, butyramide, ethanolamine, and acetamide compared with values in NGV. In contrast, gastric lipid LUV exhibited the same or lower permeabilities to urea, glycerol, and ammonia compared with values in NGV. We conclude that lipid composition alone can reconstitute membrane permeabilities to some, but not all, molecules. These results indicate that bilayer asymmetry may be required for the unique permeability of "water-tight" apical membranes and reveal different barrier mechanisms for water and protons, as opposed to ammonia, urea, and glycerol.

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Pasternak, C. A., C. L. Bashford e G. Menestrina. "Mechanisms of attack and defence at the cell surface: The use of phospholipid bilayers as models for cell membrane". Bioscience Reports 9, n. 4 (1 agosto 1989): 503–7. http://dx.doi.org/10.1007/bf01117054.

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Electrical conductivity across phospholipid bilayers induced by various cytotoxic proteins has been used to analyse the damaging action of such proteins on cells; the protective effect of divalent cations and protons against such attack has also been investigated. The predominant effect of divalent cations and protons is to promote the closed state of membrane pores, i.e. to “gate” protein-induced lesions.

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Rahmawati, Sitti, Cynthia Linaya Radiman e Muhamad Abdulkadir Martoprawiro. "Ab Initio Study of Proton Transfer and Hydration in Phosphorylated Nata de Coco". Indonesian Journal of Chemistry 17, n. 3 (30 novembre 2017): 523. http://dx.doi.org/10.22146/ijc.24895.

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This research aims to calculate energetics parameters, hydrogen bonding, characteristics local hydration, and proton transfer in phosphorylated nata de coco (NDCF) membrane using ab initio method. The minimum energy structure of NDCF membranes and the addition of n water molecules (n = 1-10) determined at the B3LYP/6-311G** level indicates that proton dissociation requires a minimum of four water molecules. Dissociated protons stabilize with the formation of (hydronium, Zundel, Eigen) ions. Calculation of the interaction energy with n water molecules indicates an increasingly negative change in energy (ΔE) and enthalpy (ΔH), and hence an increasingly positive interaction with water molecules. This interaction facilitates the transfer of protons in the membrane matrix. Calculation of the rotational energy at the center of C-O indicates that the pyranose ring structure, with a maximum barrier energies of ~ 12.5 J/mol, is much more flexible than the aromatic backbones of sulfonated poly(phenylene) sulfone (sPSO2) and the polytetrafluoroethylene (PTFE) backbones in perfluorosulfonic acid ionomers (PFSA). These energy calculations provide the basis that the flexibility of the pyranose ring and the hydrogen bonding between water molecules and phosphonate groups influence the transfer of protons in the membrane of NDCF.

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Shi, Le, Ruggero Rossi, Moon Son, Derek M. Hall, Michael A. Hickner, Christopher A. Gorski e Bruce E. Logan. "Using reverse osmosis membranes to control ion transport during water electrolysis". Energy & Environmental Science 13, n. 9 (2020): 3138–48. http://dx.doi.org/10.1039/d0ee02173c.

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A relatively inexpensive commercially available RO membrane was shown to be useful for direct seawater H₂ generation as the membrane can selectively transport protons and hydroxide ions over other salt ions, and keep the inert anolyte contained to avoid chlorine gas evolution.

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Qi, Han, Zhongwu Li, Yi Tao, Weiwei Zhao, Kabin Lin, Zhenhua Ni, Chuanhong Jin, Yan Zhang, Kedong Bi e Yunfei Chen. "Fabrication of sub-nanometer pores on graphene membrane for ion selective transport". Nanoscale 10, n. 11 (2018): 5350–57. http://dx.doi.org/10.1039/c8nr00050f.

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Junoh, Hazlina, Juhana Jaafar, Nik Abdul Hadi Md Nordin, Ahmad Fauzi Ismail, Mohd Hafiz Dzarfan Othman, Mukhlis A. Rahman, Farhana Aziz e Norhaniza Yusof. "Performance of Polymer Electrolyte Membrane for Direct Methanol Fuel Cell Application: Perspective on Morphological Structure". Membranes 10, n. 3 (25 febbraio 2020): 34. http://dx.doi.org/10.3390/membranes10030034.

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Membrane morphology plays a great role in determining the performance of polymer electrolyte membranes (PEMs), especially for direct methanol fuel cell (DMFC) applications. Membrane morphology can be divided into two types, which are dense and porous structures. Membrane fabrication methods have different configurations, including dense, thin and thick, layered, sandwiched and pore-filling membranes. All these types of membranes possess the same densely packed structural morphology, which limits the transportation of protons, even at a low methanol crossover. This paper summarizes our work on the development of PEMs with various structures and architecture that can affect the membrane’s performance, in terms of microstructures and morphologies, for potential applications in DMFCs. An understanding of the transport behavior of protons and methanol within the pores’ limits could give some perspective in the delivery of new porous electrolyte membranes for DMFC applications.

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Hill, Warren G., Eyad Almasri, W. Giovanni Ruiz, Gerard Apodaca e Mark L. Zeidel. "Water and solute permeability of rat lung caveolae: high permeabilities explained by acyl chain unsaturation". American Journal of Physiology-Cell Physiology 289, n. 1 (luglio 2005): C33—C41. http://dx.doi.org/10.1152/ajpcell.00046.2005.

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Caveolae are invaginated membrane structures with high levels of cholesterol, sphingomyelin, and caveolin protein that are predicted to exist as liquid-ordered domains with low water permeability. We isolated a caveolae-enriched membrane fraction without detergents from rat lung and characterized its permeability properties to nonelectrolytes and protons. Membrane permeability to water was 2.85 ± 0.41 × 10−3 cm/s, a value 5–10 times higher than expected based on comparisons with other cholesterol and sphingolipid-enriched membranes. Permeabilities to urea, ammonia, and protons were measured and found to be moderately high for urea and ammonia at 8.85 ± 2.40 × 10−7and 6.84 ± 1.03 × 10−2 respectively and high for protons at 8.84 ± 3.06 × 10−2 cm/s. To examine whether caveolin or other integral membrane proteins were responsible for high permeabilities, liposomes designed to mimic the lipids of the inner and outer leaflets of the caveolar membrane were made. Osmotic water permeability to both liposome compositions were determined and a combined inner/outer leaflet water permeability was calculated and found to be close to that of native caveolae at 1.58 ± 1.1 × 10−3 cm/s. In caveolae, activation energy for water flux was high (19.4 kcal/mol) and water permeability was not inhibited by HgCl2; however, aquaporin 1 was detectable by immunoblotting. Immunostaining of rat lung with AQP1 and caveolin antisera revealed very low levels of colocalization. We conclude that aquaporin water channels do not contribute significantly to the observed water flux and that caveolae have relatively high water and solute permeabilities due to the high degree of unsaturation in their fatty acyl chains.

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Khorana, H. G. "Bacteriorhodopsin, a membrane protein that uses light to translocate protons." Journal of Biological Chemistry 263, n. 16 (giugno 1988): 7439–42. http://dx.doi.org/10.1016/s0021-9258(18)68514-x.

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BRISKIN, DONALD P., e JOHN B. HANSON. "How Does the Plant Plasma Membrane H+-ATPase Pump Protons?" Journal of Experimental Botany 43, n. 3 (1992): 269–89. http://dx.doi.org/10.1093/jxb/43.3.269.

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Luoto, Heidi H., Erika Nordbo, Alexander A. Baykov, Reijo Lahti e Anssi M. Malinen. "Membrane Na+-pyrophosphatases Can Transport Protons at Low Sodium Concentrations". Journal of Biological Chemistry 288, n. 49 (24 ottobre 2013): 35489–99. http://dx.doi.org/10.1074/jbc.m113.510909.

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Negrete, H. O., J. P. Lavelle, J. Berg, S. A. Lewis e M. L. Zeidel. "Permeability properties of the intact mammalian bladder epithelium". American Journal of Physiology-Renal Physiology 271, n. 4 (1 ottobre 1996): F886—F894. http://dx.doi.org/10.1152/ajprenal.1996.271.4.f886.

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Because the mammalian bladder must store urine of composition which differs markedly from that of plasma for prolonged periods, the bladder permeability barrier must maintain extremely low permeabilities to substances which normally cross membranes relatively rapidly, such as water, protons, and small nonelectrolytes like urea and ammonia. In the present studies, permeabilities of the apical membrane of dissected rabbit bladder epithelium to water, urea, ammonia, and protons were measured in Ussing chambers and averaged (in cm/s) for water, 5.15 +/- 0.43 x 10(-5); for urea, 4.51 +/- 0.67 x 10(-6); for ammonia, 5.14 +/- 0.62 x 10(-4); and for protons, 2.98 +/- 1.87 x 10(-3), respectively. These permeability values are exceptionally low and are expected to result in minimal to no leakage of these normally permeable substances across the epithelium. Water permeabilities in intact whole rabbit bladders were indistinguishable from those obtained in the dissected epithelial preparation. Moreover, addition of nystatin to the apical solution of dissected epithelia rapidly increased water permeability in conjunction with loss of epithelial resistance. These results confirm that the apical membrane of the bladder epithelial cells represents the bladder permeability barrier. In addition, they establish a model system that will permit examination of how membrane structure reduces permeability and how epithelial injury compromises barrier function.

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30

Lanzrein, Markus, Nicole Käsermann e Christoph Kempf. "Changes in membrane permeability during semliki forest virus induced cell fusion". Bioscience Reports 12, n. 3 (1 giugno 1992): 221–36. http://dx.doi.org/10.1007/bf01121792.

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The infection of Aedes albopictus cells by Semliki Forest virus (SFV) is a non lytic event. Exposure of infected cells to mildly acidic pH (<6.2) leads to syncytium formation. This polykaryon formation is accompanied by an influex of protons into the cells (Kempf et al. Biosci. Rep. 7, 761–769, 1987). We have further investigated this permeability change using various fluorescent or radiolabeled compounds. A significant, pH dependent increase of the membrane permeability to low molecular weight compounds (Mr<1000) was observed when infected cells were exposed to a pH<6.2. The pH dependence of the peremability change was very similar to the pH dependence of cell-cell fusion. The permeability change was sensitive to divalent cations, protons and anionic antiviral drugs such as trypan blue. The nature of this virus induced, pH dependent permeability change is discussed.

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31

Kaur, Divya, Xiuhong Cai, Umesh Khaniya, Yingying Zhang, Junjun Mao, Manoj Mandal e Marilyn Gunner. "Tracing the Pathways of Waters and Protons in Photosystem II and Cytochrome c Oxidase". Inorganics 7, n. 2 (31 gennaio 2019): 14. http://dx.doi.org/10.3390/inorganics7020014.

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Photosystem II (PSII) uses water as the terminal electron donor, producing oxygen in the Mn4CaO5 oxygen evolving complex (OEC), while cytochrome c oxidase (CcO) reduces O2 to water in its heme–Cu binuclear center (BNC). Each protein is oriented in the membrane to add to the proton gradient. The OEC, which releases protons, is located near the P-side (positive, at low-pH) of the membrane. In contrast, the BNC is in the middle of CcO, so the protons needed for O2 reduction must be transferred from the N-side (negative, at high pH). In addition, CcO pumps protons from N- to P-side, coupled to the O2 reduction chemistry, to store additional energy. Thus, proton transfers are directly coupled to the OEC and BNC redox chemistry, as well as needed for CcO proton pumping. The simulations that study the changes in proton affinity of the redox active sites and the surrounding protein at different states of the reaction cycle, as well as the changes in hydration that modulate proton transfer paths, are described.

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32

Movellan, Kumar Tekwani, Eszter E. Najbauer, Supriya Pratihar, Michele Salvi, Karin Giller, Stefan Becker e Loren B. Andreas. "Alpha protons as NMR probes in deuterated proteins". Journal of Biomolecular NMR 73, n. 1-2 (14 febbraio 2019): 81–91. http://dx.doi.org/10.1007/s10858-019-00230-y.

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Abstract We describe a new labeling method that allows for full protonation at the backbone Hα position, maintaining protein side chains with a high level of deuteration. We refer to the method as alpha proton exchange by transamination (α-PET) since it relies on transaminase activity demonstrated here using Escherichia coli expression. We show that α-PET labeling is particularly useful in improving structural characterization of solid proteins by introduction of an additional proton reporter, while eliminating many strong dipolar couplings. The approach benefits from the high sensitivity associated with 1.3 mm samples, more abundant information including Hα resonances, and the narrow proton linewidths encountered for highly deuterated proteins. The labeling strategy solves amide proton exchange problems commonly encountered for membrane proteins when using perdeuteration and backexchange protocols, allowing access to alpha and all amide protons including those in exchange-protected regions. The incorporation of Hα protons provides new insights, as the close Hα–Hα and Hα–HN contacts present in β-sheets become accessible, improving the chance to determine the protein structure as compared with HN–HN contacts alone. Protonation of the Hα position higher than 90% is achieved for Ile, Leu, Phe, Tyr, Met, Val, Ala, Gln, Asn, Thr, Ser, Glu, Asp even though LAAO is only active at this degree for Ile, Leu, Phe, Tyr, Trp, Met. Additionally, the glycine methylene carbon is labeled preferentially with a single deuteron, allowing stereospecific assignment of glycine alpha protons. In solution, we show that the high deuteration level dramatically reduces R2 relaxation rates, which is beneficial for the study of large proteins and protein dynamics. We demonstrate the method using two model systems, as well as a 32 kDa membrane protein, hVDAC1, showing the applicability of the method to study membrane proteins.

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Rasi-Caldogno, Franca, Maria Chiara Pugliarello e Maria Ida De Michelis. "Electrogenic Transport of Protons Driven by the Plasma Membrane ATPase in Membrane Vesicles from Radish". Plant Physiology 77, n. 1 (1 gennaio 1985): 200–205. http://dx.doi.org/10.1104/pp.77.1.200.

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34

Muljani, S., e A. Wulanawati. "Microbial Fuel Cell Based Polystyrene Sulfonated Membrane as Proton Exchange Membrane". ALCHEMY Jurnal Penelitian Kimia 12, n. 2 (2 novembre 2016): 155. http://dx.doi.org/10.20961/alchemy.12.2.1818.155-166.

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Abstract (sommario):

Microbial fuel cell (MFC) represents a major bioelectrochemical system that converts biomass spontaneously into electricity through the activity of microorganisms. The MFC consists of anode and cathode compartments. Microorganisms in MFC liberate electrons while the electron donor is consumed. The produced electron is transmitted to the anode surface, but the generated protons must pass through the proton exchange membrane (PEM) to reach the cathode compartment. PEM, as a key factor, affects electricity generation in MFCs. The study attempted to investigate if the sulfonated polystyrene (SPS) membrane can be used as a PEM in the application on MFC. SPS membrane has been characterized using Fourier transform infrared spectrophotometer (FTIR), scanning electron microscope (SEM) and conductivity. The result of the conductivity (σ) revealed that the membrane has a promising application for MFC.

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35

Muljani, S., e A. Wulanawati. "Microbial Fuel Cell Based Polystyrene Sulfonated Membrane as Proton Exchange Membrane". ALCHEMY Jurnal Penelitian Kimia 12, n. 2 (2 novembre 2016): 155. http://dx.doi.org/10.20961/alchemy.v12i2.1818.

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Abstract (sommario):

Microbial fuel cell (MFC) represents a major bioelectrochemical system that converts biomass spontaneously into electricity through the activity of microorganisms. The MFC consists of anode and cathode compartments. Microorganisms in MFC liberate electrons while the electron donor is consumed. The produced electron is transmitted to the anode surface, but the generated protons must pass through the proton exchange membrane (PEM) to reach the cathode compartment. PEM, as a key factor, affects electricity generation in MFCs. The study attempted to investigate if the sulfonated polystyrene (SPS) membrane can be used as a PEM in the application on MFC. SPS membrane has been characterized using Fourier transform infrared spectrophotometer (FTIR), scanning electron microscope (SEM) and conductivity. The result of the conductivity (σ) revealed that the membrane has a promising application for MFC.

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36

Kageyama, Miho, Beste Balci, Shotaro Danjo, Kimiyo Nakamichi e Motoaki Kawase. "Hydrogen and Oxygen Permeability through PEFC Membrane and Membrane Electrode Assembly". ECS Transactions 112, n. 4 (29 settembre 2023): 291–303. http://dx.doi.org/10.1149/11204.0291ecst.

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Abstract (sommario):

A proton exchange membrane (PEM) is an important component of a polymer electrolyte fuel cell (PEFC) from the viewpoint of proton transport. Only protons are desired to be transported through a membrane, but the feed gases also permeate. The permeation of the feed gas through a membrane affects the PEFC performance. Temperature and relative humidity dependencies of the hydrogen and oxygen permeability through a perfluorosulfonic acid (PFSA) membrane were measured. By considering that a membrane consists of three layers, i.e. a bulk layer sandwiched between skin layers, the transport properties of each layer were separated. The bulk layer effective diffusion coefficients of hydrogen and oxygen through both a PEM and an MEA were formulated as a function of temperature and RH. The oxygen transfer coefficient in the skin layer increased with RH, whereas the hydrogen transfer coefficient was almost constant regardless of RH.

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37

Nesterov, Semen V., Lev S. Yaguzhinsky, Raif G. Vasilov, Vasiliy N. Kadantsev e Alexey N. Goltsov. "Contribution of the Collective Excitations to the Coupled Proton and Energy Transport along Mitochondrial Cristae Membrane in Oxidative Phosphorylation System". Entropy 24, n. 12 (13 dicembre 2022): 1813. http://dx.doi.org/10.3390/e24121813.

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Abstract (sommario):

The results of many experimental and theoretical works indicate that after transport of protons across the mitochondrial inner membrane (MIM) in the oxidative phosphorylation (OXPHOS) system, they are retained on the membrane–water interface in nonequilibrium state with free energy excess due to low proton surface-to-bulk release. This well-established phenomenon suggests that proton trapping on the membrane interface ensures vectorial lateral transport of protons from proton pumps to ATP synthases (proton acceptors). Despite the key role of the proton transport in bioenergetics, the molecular mechanism of proton transfer in the OXPHOS system is not yet completely established. Here, we developed a dynamics model of long-range transport of energized protons along the MIM accompanied by collective excitation of localized waves propagating on the membrane surface. Our model is based on the new data on the macromolecular organization of the OXPHOS system showing the well-ordered structure of respirasomes and ATP synthases on the cristae membrane folds. We developed a two-component dynamics model of the proton transport considering two coupled subsystems: the ordered hydrogen bond (HB) chain of water molecules and lipid headgroups of MIM. We analytically obtained a two-component soliton solution in this model, which describes the motion of the proton kink, corresponding to successive proton hops in the HB chain, and coherent motion of a compression soliton in the chain of lipid headgroups. The local deformation in a soliton range facilitates proton jumps due to water molecules approaching each other in the HB chain. We suggested that the proton-conducting structures formed along the cristae membrane surface promote direct lateral proton transfer in the OXPHOS system. Collective excitations at the water–membrane interface in a form of two-component soliton ensure the coupled non-dissipative transport of charge carriers and elastic energy of MIM deformation to ATP synthases that may be utilized in ATP synthesis providing maximal efficiency in mitochondrial bioenergetics.

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38

Vergara, Eva, Gonzalo Neira, Carolina González, Diego Cortez, Mark Dopson e David S. Holmes. "Evolution of Predicted Acid Resistance Mechanisms in the Extremely Acidophilic Leptospirillum Genus". Genes 11, n. 4 (3 aprile 2020): 389. http://dx.doi.org/10.3390/genes11040389.

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Abstract (sommario):

Organisms that thrive in extremely acidic environments (≤pH 3.5) are of widespread importance in industrial applications, environmental issues, and evolutionary studies. Leptospirillum spp. constitute the only extremely acidophilic microbes in the phylogenetically deep-rooted bacterial phylum Nitrospirae. Leptospirilli are Gram-negative, obligatory chemolithoautotrophic, aerobic, ferrous iron oxidizers. This paper predicts genes that Leptospirilli use to survive at low pH and infers their evolutionary trajectory. Phylogenetic and other bioinformatic approaches suggest that these genes can be classified into (i) “first line of defense”, involved in the prevention of the entry of protons into the cell, and (ii) neutralization or expulsion of protons that enter the cell. The first line of defense includes potassium transporters, predicted to form an inside positive membrane potential, spermidines, hopanoids, and Slps (starvation-inducible outer membrane proteins). The “second line of defense“ includes proton pumps and enzymes that consume protons. Maximum parsimony, clustering methods, and gene alignments are used to infer the evolutionary trajectory that potentially enabled the ancestral Leptospirillum to transition from a postulated circum-neutral pH environment to an extremely acidic one. The hypothesized trajectory includes gene gains/loss events driven extensively by horizontal gene transfer, gene duplications, gene mutations, and genomic rearrangements.

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39

Stainbrook, Sarah C., e Joseph M. Jez. "Protecting P-type plasma membrane H+-ATPases from ROS". Biochemical Journal 478, n. 8 (21 aprile 2021): 1511–13. http://dx.doi.org/10.1042/bcj20210109.

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Abstract (sommario):

P-type ATPase are ubiquitous transport proteins across all kingdoms of life. These proteins share a common mechanism involving phosphorylation of an invariant aspartate to facilitate movement of substrates from protons to phospholipids across cellular membranes. In this issue of the Biochemical Journal, Welle et al. identify a conserved cysteine near the functionally critical aspartate of P-type plasma membrane H+-ATPases that protects the protein from reactive oxygen species.

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40

Fliegel, Larry. "Structural and Functional Changes in the Na+/H+ Exchanger Isoform 1, Induced by Erk1/2 Phosphorylation". International Journal of Molecular Sciences 20, n. 10 (14 maggio 2019): 2378. http://dx.doi.org/10.3390/ijms20102378.

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Abstract (sommario):

The human Na+/H+ exchanger isoform 1 (NHE1) is a plasma membrane transport protein that plays an important role in pH regulation in mammalian cells. Because of the generation of protons by intermediary metabolism as well as the negative membrane potential, protons accumulate within the cytosol. Extracellular signal-regulated kinase (ERK)-mediated regulation of NHE1 is important in several human pathologies including in the myocardium in heart disease, as well as in breast cancer as a trigger for growth and metastasis. NHE1 has a N-terminal, a 500 amino acid membrane domain, and a C-terminal 315 amino acid cytosolic domain. The C-terminal domain regulates the membrane domain and its effects on transport are modified by protein binding and phosphorylation. Here, we discuss the physiological regulation of NHE1 by ERK, with an emphasis on the critical effects on structure and function. ERK binds directly to the cytosolic domain at specific binding domains. ERK also phosphorylates NHE1 directly at multiple sites, which enhance NHE1 activity with subsequent downstream physiological effects. The NHE1 cytosolic regulatory tail possesses both ordered and disordered regions, and the disordered regions are stabilized by ERK-mediated phosphorylation at a phosphorylation motif. Overall, ERK pathway mediated phosphorylation modulates the NHE1 tail, and affects the activity, structure, and function of this membrane protein.

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41

Weichselbaum, Ewald, Timur Galimzyanov, Oleg V. Batishchev, Sergey A. Akimov e Peter Pohl. "Proton Migration on Top of Charged Membranes". Biomolecules 13, n. 2 (11 febbraio 2023): 352. http://dx.doi.org/10.3390/biom13020352.

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Abstract (sommario):

Proton relay between interfacial water molecules allows rapid two-dimensional diffusion. An energy barrier, ΔGr‡, opposes proton-surface-to-bulk release. The ΔGr‡-regulating mechanism thus far has remained unknown. Here, we explored the effect interfacial charges have on ΔGr‡’s enthalpic and entropic constituents, ΔGH‡ and ΔGS‡, respectively. A light flash illuminating a micrometer-sized membrane patch of a free-standing planar lipid bilayer released protons from an adsorbed hydrophobic caged compound. A lipid-anchored pH-sensitive dye reported protons’ arrival at a distant membrane patch. Introducing net-negative charges to the bilayer doubled ΔGH‡, while positive net charges decreased ΔGH‡. The accompanying variations in ΔGS‡ compensated for the ΔGH‡ modifications so that ΔGr‡ was nearly constant. The increase in the entropic component of the barrier is most likely due to the lower number and strength of hydrogen bonds known to be formed by positively charged residues as compared to negatively charged moieties. The resulting high ΔGr‡ ensured interfacial proton diffusion for all measured membranes. The observation indicates that the variation in membrane surface charge alone is a poor regulator of proton traffic along the membrane surface.

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42

Hildebrandt, V., K. Fendler, J. Heberle, A. Hoffmann, E. Bamberg e G. Buldt. "Bacteriorhodopsin expressed in Schizosaccharomyces pombe pumps protons through the plasma membrane." Proceedings of the National Academy of Sciences 90, n. 8 (15 aprile 1993): 3578–82. http://dx.doi.org/10.1073/pnas.90.8.3578.

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43

Edman, K., P. Nollert, A. Royant, H. Belrhali, E. Pebay-Peyroula, T. Ursby, J. Hajdu, R. Neutze e E. M. Landau. "Portrait of a membrane protein in action: bacterio-rhodopsin pumping protons". Acta Crystallographica Section A Foundations of Crystallography 56, s1 (25 agosto 2000): s265. http://dx.doi.org/10.1107/s0108767300025666.

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44

Sladkov, K. D., e S. S. Kolesnikov. "Model of a Molecular Proton Sensor in Taste Cells". Биологические мембраны Журнал мембранной и клеточной биологии 40, n. 3 (1 maggio 2023): 188–93. http://dx.doi.org/10.31857/s023347552303009x.

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Abstract (sommario):

Otopetrins represents a group of membrane proteins that function as proton-selective ion channels. Existing evidence indicates that Otop1, the eponym of the family, is a likely molecular sensor of protons involved in detecting acid stimuli in taste cells of type III. Acid stimuli is believed to initiate an inward current carried by protons through receptive apical membrane to depolarize a type III cell and trigger a train of action potentials driving afferent neurotransmission. While many details of this rather complicated process have not been uncovered yet, mathematical modelling could provide a sufficient insight into sour transduction. Here we present a mathematical model for describing dynamic and transport properties of Otop1 channel. The elaborated model appropriately describes proton currents through Otop1 under different conditions, and it could be employed for further modeling of sour responses of taste cells.

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45

Berg, Jamie R., Christian M. Spilker e Simon A. Lewis. "Modulation of polymyxin B effects on mammalian urinary bladder". American Journal of Physiology-Renal Physiology 275, n. 2 (1 agosto 1998): F204—F215. http://dx.doi.org/10.1152/ajprenal.1998.275.2.f204.

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Abstract (sommario):

This report demonstrates that Ca2+, Mg2+, and protons alter the ability of polymyxin B (PX, a cationic antibiotic used clinically as a bactericidal agent) to increase the apical membrane conductance of the rabbit urinary bladder. Using electrophysiological methods, we determine that these alterations occur by two mechanisms. First, they blocked the PX-induced conductance in a rapid and reversible manner; second, they competed with PX for a membrane binding site. In addition, Ca2+(but not Mg2+or protons) altered the rate at which the induced conductance could be reversed. When solution pH was greater than 8.8, PX was not able to induce a conductance. This ability of high pH to inhibit the action of PX was due to a decrease in the number of positive charges on PX. Further studies demonstrated that for maximal activity, PX required its fatty acid tail. These data were used to develop a model describing the mechanism by which PX can induce a conductance in the apical membrane of the rabbit urinary bladder.

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46

Moreno Ostertag, Laila, Xiao Ling, Katrin F. Domke, Sapun H. Parekh e Markus Valtiner. "Characterizing the hydrophobic-to-hydrophilic transition of electrolyte structuring in proton exchange membrane mimicking surfaces". Physical Chemistry Chemical Physics 20, n. 17 (2018): 11722–29. http://dx.doi.org/10.1039/c8cp01625a.

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Abstract (sommario):

The surface density of charged sulfonic acid head groups in a perfluorosulfonic acid (PFSA) proton exchange membrane determines the hydrophilicity of the ionic channels and is thus critical for the structuring and transport of water and protons.

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47

Bashford, C. Lindsay. "Membrane pores—From biology to track-etched membranes". Bioscience Reports 15, n. 6 (1 dicembre 1995): 553–65. http://dx.doi.org/10.1007/bf01204357.

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Abstract (sommario):

Flow of ions through narrow pores, either induced in biological membranes or created in synthetic membrane filters, exhibits, under appropriate conditions: 1) rapid switching of ion current between high and low conducting states; 2) selectivity between different ions; 3) inhibition by protons or divalent cations with an order of efficacy usually H+ >Zn2+>Ca2+ >Mg2+. It seems reasonable to conclude that these common properties arise from a common cause-the nature of the flow of ions close to a charged surface.

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48

Yang, Shuai-Liang, Yue-Ying Yuan, Fei Ren, Chen-Xi Zhang e Qing-Lun Wang. "High proton conductivity in a nickel(ii) complex and its hybrid membrane". Dalton Transactions 48, n. 6 (2019): 2190–96. http://dx.doi.org/10.1039/c8dt04171g.

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Abstract (sommario):

A novel 2D nickel(ii) complex (1) has been successfully synthesized using a 2,2′-bipyridyl, polycarboxylsulfonate ligand H₄SBTC and Ni²⁺ ions. Owing to the presence of abundant water molecules, hydrogen bond networks and other protons, 1 and its hybrid membranes demonstrate high proton conductivity.

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49

STUCHEBRUKHOV, ALEXEI A. "ELECTRON TRANSFER REACTIONS COUPLED TO PROTON TRANSLOCATION: CYTOCHROME OXIDASE, PROTON PUMPS, AND BIOLOGICAL ENERGY TRANSDUCTION". Journal of Theoretical and Computational Chemistry 02, n. 01 (marzo 2003): 91–118. http://dx.doi.org/10.1142/s0219633603000318.

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Abstract (sommario):

Cytochrome oxidase (COX) is the terminal component of electron transport chain of the respiratory system in mitochondria, and one of the key enzymes responsible for energy generation in cells. COX functions as a proton pump that utilizes free energy of oxygen reduction for translocation of protons across the mitochondrion membrane. The proton gradient created in the process is later utilized to drive synthesis of ATP. Although the structure of COX has been recently resolved, the molecular mechanism of proton pumping remains unknown. In this paper, general principles and possible molecular mechanisms of energy transformations in this enzyme will be discussed. The main question is how exactly chemical energy of oxygen reduction and water formation is transformed into a proton gradient; or, how exactly electron transfer reactions are utilized to translocate protons across the mitochondrion membrane against the electrochemical gradient. A key to the solution of this problem is in understanding correlated transport of electrons and protons. Here, theoretical models are discussed for coupled electron and proton transfer reactions in which an electron is tunneling over long distance between two redox cofactors, and a coupled proton is moving along a proton conducting channel in a classical, diffusion-like random walk fashion. Such reactions are typical for COX and other enzymes involved in biological energy transformations.

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50

Epalle, Nathan Hugo, e Eric Beitz. "Local Attraction of Substrates and Co-Substrates Enhances Weak Acid and Base Transmembrane Transport". Biomolecules 12, n. 12 (30 novembre 2022): 1794. http://dx.doi.org/10.3390/biom12121794.

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Abstract (sommario):

The transmembrane transport of weak acid and base metabolites depends on the local pH conditions that affect the protonation status of the substrates and the availability of co-substrates, typically protons. Different protein designs ensure the attraction of substrates and co-substrates to the transporter entry sites. These include electrostatic surface charges on the transport proteins and complexation with seemingly transport-unrelated proteins that provide substrate and/or proton antenna, or enzymatically generate substrates in place. Such protein assemblies affect transport rates and directionality. The lipid membrane surface also collects and transfers protons. The complexity in the various systems enables adjustability and regulation in a given physiological or pathophysiological situation. This review describes experimentally shown principles in the attraction and facilitation of weak acid and base transport substrates, including monocarboxylates, ammonium, bicarbonate, and arsenite, plus protons as a co-substrate.

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