Internal electrostatic potentials in bilayers: measuring and controlling dipole potentials in lipid vesicles. Biophys. J. 65: 289-299

Department of Chemistry, University of Virginia, Charlottesville 22901.
Biophysical Journal (Impact Factor: 3.97). 08/1993; 65(1):289-99. DOI: 10.1016/S0006-3495(93)81051-8
Source: PubMed


The binding and translocation rates of hydrophobic cation and anion spin labels were measured in unilamellar vesicle systems formed from phosphatidylcholine. As a result of the membrane dipole potential, the binding and translocation rates for oppositely charged hydrophobic ions are dramatically different. These differences were analyzed using a simple electrostatic model and are consistent with the presence of a dipole potential of approximately 280 mV in phosphatidylcholine. Phloretin, a molecule that reduces the magnitude of the dipole potential, increases the translocation rate of hydrophobic cations, while decreasing the rate for anions. In addition, phloretin decreases the free energy of binding of the cation, while increasing the free energy of binding for the anion. The incorporation of 6-ketocholestanol also produces differential changes in the binding and translocation rates of hydrophobic ions, but in an opposite direction to those produced by phloretin. This is consistent with the view that 6-ketocholestanol increases the magnitude of the membrane dipole potential. A quantitative analysis of the binding and translocation rate changes produced by ketocholestanol and phloretin is well accounted for by a point dipole model that includes a dipole layer due to phloretin or 6-ketocholestanol in the membrane-solution interface. This approach allows dipole potentials to be estimated in membrane vesicle systems and permits predictable, quantitative changes in the magnitude of the internal electrostatic field in membranes. Using phloretin and 6-ketocholestanol, the dipole potential can be altered by over 200 mV in phosphatidylcholine vesicles.

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    • "The dipole potential of THP-1 cells was modulated by the addition of 6-ketocholestanol (6-KC, see Fig. 1) [9]. As a reference probe, we used di-8-ANEPPS [6] (Fig. 1). "
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    • "Interaction of Polylysines with the Surface of Lipid Membranes component cannot be measured directly but its deviations may be controlled indirectly by different dipole sensitive probes [55] [57] [59] [60] or by subtracting electric field changes in the diffuse part of EDL (zeta-potentials) from total BP that comes, for instance, from direct Volta potential measurements at lipid monolayer [37] [55] or from IFC measurements with planar BLM. The latter method, described in detail in Ref. [32], assumes that the planar BLM conductivity remains negligible in the presence of adsorbed polymer and this condition has to be carefully controlled because PL of high-molecular weight decrease the BLM stability to applied external voltage [14]. "
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    ABSTRACT: The topic correlates electrostatic effects induced by polylysine (PL) adsorption at the lipid membrane surface with data of alternative methods sensitive to lipid bilayer structure. Comparison of electrokinetic data for liposomes from anionic lipids (cardiolipin, phosphatidylserine) and results of boundary potential (BP) measurements with lipid membranes shows effects in two opposite directions: fast positive changes of BP due to adsorption of polycations at the outer membrane surface and slow negative changes that can be attributed to alteration of the dipole component of BP. The latter effect does not depend on the polymer length and may be caused by lipid interaction with lysine as a basic unit of these polypeptides. Molecular dynamic simulation points out the possible mechanism of the dipole effect, which could be caused by reduced number of H-bonds to PO4 groups upon the lysine adsorption. Atomic force microscopy visualized the geometry of clusters formed by PL of different lengths at the lipid bilayer. Isotherm titration calorimetry and the technique of lipid monolayers reveal the similarity in polypeptide and inorganic multivalent cation effects on the lateral lipid condensation accompanied by dipole effects.
    Advances in Planar Lipid Bilayers and Liposomes 01/2013; 17(29):139-166. DOI:10.1016/B978-0-12-411516-3.00006-1
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    • "301.8 mV [28], and the potential of a pure DMPC vesicle is 410 mV, while the value for a hybrid DMPC/MMPC vesicle is 268 mV [29]. Another way to modify the membrane dipole potential is to add specific compounds to the solution [30] [31] [32] [33]. Among these compounds, 6-ketocholestanol (6-KC) increases ψ d , while phloretin and phlorizin decrease it. "
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    ABSTRACT: The implicit membrane model IMM1 is extended to include the membrane dipole potential and applied to molecular dynamics simulations of the helical peptides alamethicin, WALP23, influenza hemagglutinin fusion peptide, HIV fusion peptide, magainin, and the pre-sequence of cytochrome c oxidase subunit IV (p25). The results show that the orientation of the peptides in the membrane can be influenced by the dipole potential. The binding affinity of all peptides except for the hemagglutinin fusion peptide decreases upon increase of the dipole potential. The changes in both orientation and binding affinity are explained by the interaction of the dipole potential with the helix backbone dipole and ionic side-chains. In general, peptides that tend to insert the N-terminus in the membrane and/or have positively charged side chains will lose binding affinity upon increase of the dipole potential.
    Biophysical chemistry 10/2011; 161:1-7. DOI:10.1016/j.bpc.2011.10.002 · 1.99 Impact Factor
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