The Experts below are selected from a list of 45 Experts worldwide ranked by ideXlab platform
David C Gadsby - One of the best experts on this subject based on the ideXlab platform.
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peering into an atpase ion Pump with single Channel recordings
Philosophical Transactions of the Royal Society B, 2009Co-Authors: David C Gadsby, Ayako Takeuchi, Pablo Artigas, Nicolas ReyesAbstract:In principle, an ion Channel needs no more than a single gate, but a Pump requires at least two gates that open and close alternately to allow ion access from only one side of the membrane at a time. In the Na+,K+-ATPase Pump, this alternating gating effects outward transport of three Na+ ions and inward transport of two K+ ions, for each ATP hydrolysed, up to a hundred times per second, generating a measurable current if assayed in millions of Pumps. Under these assay conditions, voltage jumps elicit brief charge movements, consistent with displacement of ions along the ion pathway while one gate is open but the other closed. Binding of the marine toxin, palytoxin, to the Na+,K+-ATPase uncouples the two gates, so that although each gate still responds to its physiological ligand they are no longer constrained to open and close alternately, and the Na+,K+-ATPase is transformed into a gated cation Channel. Millions of Na+ or K+ ions per second flow through such an open Pump–Channel, permitting assay of single molecules and allowing unprecedented access to the ion transport pathway through the Na+,K+-ATPase. Use of variously charged small hydrophilic thiol-specific reagents to probe cysteine targets introduced throughout the Pump's transmembrane segments allows mapping and characterization of the route traversed by transported ions.
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ion occlusion deocclusion partial reactions in individual palytoxin modified na k Pumps
Annals of the New York Academy of Sciences, 2003Co-Authors: Pablo Artigas, David C GadsbyAbstract:In P-type ion-motive ATPases, transported ions approach their binding sites from one membrane surface, become buried deep within "occluded" conformations in which the sites are inaccessible from either mem- brane side, and are then deoccluded and released to the opposite membrane surface. This describes an alternating-gate transport mechanism, in which the Pump acts like an ion Channel with two gates that open and close alternately. The occluded states ensure that one gate closes before the other can open, thus preventing the large electrodiffusive ion fluxes that would otherwise quickly undo the Pump's electrochemical work. High-resolution crystal structures of two conformations of the SERCA (sarcoplasmic and endoplasmic reticulum Ca 2+ ) P-type ATPase, together with mutagenesis results and analyses of structural models based on homology, have begun to provide a picture of the ion coordination sites in related P-type ATPases, including the Na/K Pump. However, in no P-type ATPase are the structures and mechanisms of the gates known. The marine toxin, palytoxin (PTX), is known to bind to the Na/K Pump and elicit a nonselective cation leak pathway, possibly by disrupting the strict coupling between the Pump's inner and outer gates, allowing them to both be open. We recently found that ion flow through PTX-modified Na/K Pump- Channels appears to be modulated by two gates that can be regulated by the Pump's physiological ligands in a manner suggesting that gating reflects underlying ion occlusion/deocclusion partial reactions. We review that work here and provide evidence that the pore of the PTX-induced Pump-Channel has a diameter > 6 A.
Nicolas Reyes - One of the best experts on this subject based on the ideXlab platform.
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peering into an atpase ion Pump with single Channel recordings
Philosophical Transactions of the Royal Society B, 2009Co-Authors: David C Gadsby, Ayako Takeuchi, Pablo Artigas, Nicolas ReyesAbstract:In principle, an ion Channel needs no more than a single gate, but a Pump requires at least two gates that open and close alternately to allow ion access from only one side of the membrane at a time. In the Na+,K+-ATPase Pump, this alternating gating effects outward transport of three Na+ ions and inward transport of two K+ ions, for each ATP hydrolysed, up to a hundred times per second, generating a measurable current if assayed in millions of Pumps. Under these assay conditions, voltage jumps elicit brief charge movements, consistent with displacement of ions along the ion pathway while one gate is open but the other closed. Binding of the marine toxin, palytoxin, to the Na+,K+-ATPase uncouples the two gates, so that although each gate still responds to its physiological ligand they are no longer constrained to open and close alternately, and the Na+,K+-ATPase is transformed into a gated cation Channel. Millions of Na+ or K+ ions per second flow through such an open Pump–Channel, permitting assay of single molecules and allowing unprecedented access to the ion transport pathway through the Na+,K+-ATPase. Use of variously charged small hydrophilic thiol-specific reagents to probe cysteine targets introduced throughout the Pump's transmembrane segments allows mapping and characterization of the route traversed by transported ions.
Larisa A Vasilets - One of the best experts on this subject based on the ideXlab platform.
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functional role of the n terminus of na k atpase α subunit as an inactivation gate of palytoxin induced Pump Channel
Biochimica et Biophysica Acta, 2003Co-Authors: Larisa A Vasilets, Kazuo Takeda, Masaru Kawamura, Wolfgang SchwarzAbstract:Abstract The N-terminus of the Na+,K+-ATPase α-subunit shows some homology to that of Shaker-B K+ Channels; the latter has been shown to mediate the N-type Channel inactivation in a ball-and-chain mechanism. When the Torpedo Na+,K+-ATPase is expressed in Xenopus oocytes and the Pump is transformed into an ion Channel with palytoxin (PTX), the Channel exhibits a time-dependent inactivation gating at positive potentials. The inactivation gating is eliminated when the N-terminus is truncated by deleting the first 35 amino acids after the initial methionine. The inactivation gating is restored when a synthetic N-terminal peptide is applied to the truncated Pumps at the intracellular surface. Truncated Pumps generate no electrogenic current and exhibit an altered stoichiometry for active transport. Thus, the N-terminus of the α-subunit appears to act like an inactivation gate and performs a critical step in the Na+,K+-ATPase Pumping function.
Govind P Agrawal - One of the best experts on this subject based on the ideXlab platform.
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effects of polarization mode dispersion on cross phase modulation in dispersion managed wavelength division multiplexed systems
Journal of Lightwave Technology, 2004Co-Authors: Govind P AgrawalAbstract:This paper develops a vector theory of cross-phase modulation (XPM) in optical fibers and use it to investigate the impact of polarization-mode dispersion (PMD) on the crosstalk induced by XPM in wavelength-division multiplexed lightwave systems. Under certain reasonable approximations, the theory permits us to obtain an analytic expression for the amplitude of probe fluctuations induced by a copropagating Pump Channel through XPM. We use this expression to calculate the average level of XPM-induced crosstalk together with its variance for several dispersion maps. We show that PMD not only reduces the crosstalk on average, but also impacts the efficiency of a commonly used polarization-interleaving technique.
Pablo Artigas - One of the best experts on this subject based on the ideXlab platform.
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peering into an atpase ion Pump with single Channel recordings
Philosophical Transactions of the Royal Society B, 2009Co-Authors: David C Gadsby, Ayako Takeuchi, Pablo Artigas, Nicolas ReyesAbstract:In principle, an ion Channel needs no more than a single gate, but a Pump requires at least two gates that open and close alternately to allow ion access from only one side of the membrane at a time. In the Na+,K+-ATPase Pump, this alternating gating effects outward transport of three Na+ ions and inward transport of two K+ ions, for each ATP hydrolysed, up to a hundred times per second, generating a measurable current if assayed in millions of Pumps. Under these assay conditions, voltage jumps elicit brief charge movements, consistent with displacement of ions along the ion pathway while one gate is open but the other closed. Binding of the marine toxin, palytoxin, to the Na+,K+-ATPase uncouples the two gates, so that although each gate still responds to its physiological ligand they are no longer constrained to open and close alternately, and the Na+,K+-ATPase is transformed into a gated cation Channel. Millions of Na+ or K+ ions per second flow through such an open Pump–Channel, permitting assay of single molecules and allowing unprecedented access to the ion transport pathway through the Na+,K+-ATPase. Use of variously charged small hydrophilic thiol-specific reagents to probe cysteine targets introduced throughout the Pump's transmembrane segments allows mapping and characterization of the route traversed by transported ions.
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ion occlusion deocclusion partial reactions in individual palytoxin modified na k Pumps
Annals of the New York Academy of Sciences, 2003Co-Authors: Pablo Artigas, David C GadsbyAbstract:In P-type ion-motive ATPases, transported ions approach their binding sites from one membrane surface, become buried deep within "occluded" conformations in which the sites are inaccessible from either mem- brane side, and are then deoccluded and released to the opposite membrane surface. This describes an alternating-gate transport mechanism, in which the Pump acts like an ion Channel with two gates that open and close alternately. The occluded states ensure that one gate closes before the other can open, thus preventing the large electrodiffusive ion fluxes that would otherwise quickly undo the Pump's electrochemical work. High-resolution crystal structures of two conformations of the SERCA (sarcoplasmic and endoplasmic reticulum Ca 2+ ) P-type ATPase, together with mutagenesis results and analyses of structural models based on homology, have begun to provide a picture of the ion coordination sites in related P-type ATPases, including the Na/K Pump. However, in no P-type ATPase are the structures and mechanisms of the gates known. The marine toxin, palytoxin (PTX), is known to bind to the Na/K Pump and elicit a nonselective cation leak pathway, possibly by disrupting the strict coupling between the Pump's inner and outer gates, allowing them to both be open. We recently found that ion flow through PTX-modified Na/K Pump- Channels appears to be modulated by two gates that can be regulated by the Pump's physiological ligands in a manner suggesting that gating reflects underlying ion occlusion/deocclusion partial reactions. We review that work here and provide evidence that the pore of the PTX-induced Pump-Channel has a diameter > 6 A.
