The Interaction Between Lipid Bilayers

While one can, in principle, explain the swelling of bilayers upon addition of salt even by assuming that the Hamaker constant does not depend on the electrolyte concentration, this was not the purpose of this paper. Note that the value -ff = 9 Debyes employed in the previous calculations is too large for surface dipoles. We fully agree with Petrache et al. that the Hamaker constant is decreased by the addition of salt, maybe not as much as 75% but nevertheless by a measurable quantity. What we tried to emphasize here is that there are so many unknown quantities in the interactions between lipid bilayers, that it is very difficult to obtain reliable information for the dependence of the Hamaker constant on electrolyte concentrations from this type of experiments. 

The stability of colloidal systems consisting of charged particles can be essentially explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory [1-7]. According to this theory, the stability of a suspension of colloidal particles is determined by the balance between the electrostatic interaction and the van der Waals interaction between particles. A number of studies on colloid stability are based on the DLVO theory. In this chapter, as an example, we consider the interaction between lipid bilayers, which serves as a model for cell-cell interactions [8, 9]. Then, we consider some aspects of the interaction between two soft spheres, by taking into account both the electrostatic and van der Waals interactions acting between them. 

The idea that out-of-plane undulations could lead to repulsive Interactions between lipid bilayers was hrst proposed by Helfrlch In the late 1970s. 

Hence, the interaction between lipid molecules is very similar in these foam bilayers and it can be supposed that the AF foam bilayers are in the liquid crystalline state within the temperature range studied. This assumption is in agreement with the fact that amniotic fluid contains substantial amount of unsaturated phospholipids, which as known [45], lower considerably the temperature of the chain-melting phase transition. Bearing in mind the similarity of the phase behaviour of a phosphatidylcholine aqueous dispersion and foam bilayers [38-40], it can be supposed that at the temperatures which are important for in vivo systems, the foam bilayers are in the liquid crystalline state. This assumption allows to determine the critical concentration of phosphatidylcholines in amniotic fluid, necessary for formation of a foam bilayer by extrapolation of the Arrhenius dependence of C, for AF foam bilayers to 37°C. Thus, at 37°C C, = 19.9 jxg cm 3 and d, = 1.47. This value of C, at 37°C corresponds to the lower limit (found by other methods [46,47]) of phosphatidylcholine concentration which permits to classify as mature a sample of amniotic fluid. The above value... 

In parallel, another important (although less direct) technique for measuring forces between macromolecules or lipid bilayers was developed, namely, the osmotic stress method [39-41]. A dispersion of vesicles or macromolecules is equilibrated with a reservoir solution containing water and other small solutes, which can freely exchange with the dispersion phase. The reservoir also contains a polymer that cannot diffuse into the dispersion. The polymer concentration determines the osmotic stress acting on the dispersion. The spacing between the macromolecules or vesicles is measured by X-ray diffraction (XRD). In this way, one obtains pressure-versus-distance curves. The osmotic stress method is used to measure interactions between lipid bilayers, DNA, polysaccharides, proteins, and other macromolecules [36]. It was particularly successful in studying the hydration... 

While the v-a plots for ionized monolayers often show no distinguishing features, it is entirely possible for such to be present and, in fact, for actual phase transitions to be observed. This was the case for films of poly(4-vinylpyri-dinium) bromide at the air-aqueous electrolyte interface [118]. In addition, electrostatic interactions play a large role in the stabilization of solid-supported lipid monolayers [119] as well as in the interactions between bilayers [120]. 

Baumgartner and coworkers [145,146] study lipid-protein interactions in lipid bilayers. The lipids are modeled as chains of hard spheres with heads tethered to two virtual surfaces, representing the two sides of the bilayer. Within this model, Baumgartner [145] has investigated the influence of membrane curvature on the conformations of a long embedded chain (a protein ). He predicts that the protein spontaneously localizes on the inner side of the membrane, due to the larger fluctuations of lipid density there. Sintes and Baumgartner [146] have calculated the lipid-mediated interactions between cylindrical inclusions ( proteins ). Apart from the... 

Structural properties of both AFA-PLN and WT-PLN bound to SER-CAla after reconstitution in a functional lipid bilayer environment were examined by 13C solid-state NMR.241 Chemical-shift assignments in all domains of AFA-PLN provide direct evidence for the presence of two terminal ot-helices connected by a linker region of reduced structural order that differs from previous findings on free PLN. A combination of the spectroscopic data with biophysical and biochemical data using flexible protein-protein docking simulations provides a structural basis for understanding the interaction between PLN and SERCala.244 Using a... 

Zdzislaw, S. Goran, L. Gordon, T., Plasmon waveguide resonance and impedance spectros copy studies of the interaction between penetratin and supported lipid bilayer membranes, Biophys. J. 2003, 84, 1796 1807... 

Bolard J, Seigneuret M, Boudet G. Interaction between phospholipid bilayer membranes and the polyene antibiotic amphotericin B lipid state and cholesterol content dependence. Biochim Biophys Acta 1980 599 280. 

Fig.3 A migrating zone of solute molecules (spots) interacting with lipid bilayers (rings) in a chromatographic or electrophoretic separation system. The free solute molecules move (arrows) relative to the liposomes or vesicles in a flow of eluent or in an electric field. The solute molecules may either partition into the membranes and diffuse between the external and internal aqueous compartments of the structures as depicted, or interact with the external surface of the membranes and stay outside.

Some membrane proteins contain one or more covalently linked lipids of several types long-chain fatty acids, isoprenoids, sterols, or glycosylated derivatives of phosphatidylmositol, GPI (Fig. 11-14). The attached lipid provides a hydrophobic anchor that inserts into the lipid bilayer and holds the protein at the membrane surface. The strength of the hydrophobic interaction between a bilayer and a single hydrocarbon chain linked to a protein is barely enough to anchor the protein securely, but many proteins have more than one attached... 

The primary biochemical defects of HS are linked to proteins important to the interaction between the membrane skeleton and the lipid bilayer involving a- and /3-spectrin, ankyrin, band 3, and protein 4.2 (Gallagher and Forget, 1998). Combined spectrin and ankyrin deficiency (Coetzer et al, 1988 Pekrun et al, 1993 Sawides et al., 1993) is most commonly observed, followed by band 3 deficiency (Iolascon et al, 1992 Jarolim et al,... 

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