Bilayer model

The most successful continuum description of membrane elasticity, dynamics, and thermodynamics is based on the smectic bilayer model (for examples of different versions and applications of this approach see Ref. 76-82 and references therein). We introduce this model in conjunction with the question of membrane undulations. 

Baumgartner, A. (1994). Asymmetries of a curved bilayer model membrane, J. Chem. Phys., 101, 9060-9062. 

Figure 4.1-15 Experimental reflectivity data (points) compared with a five-bilayer model (solid line) for a 156 A thick [CigMIMHPFe] films at 298 K. Reproduced from reference 54 with permission.

It is possible that quite different molecular architectures may occur in membranes from different sources. Current research may result in a much more dramatic revision or complete rejection of the bilayer model for some membranes, especially in such systems as mitochondria (30) and chloroplasts (2). However, it is also possible that structural differences are only variations on the basic theme of the bilayer, from myelin at one extreme to mitochondria or chloroplasts on the other. One must not readily reject the fundamentals of the Danielli concept, especially in view of the present inadequate knowledge of the properties of phospholipids in water. Clearly the molecular architecture of membranes is speculative, but most aspects of the problem are amenable to direct experimental test by the new physical techniques. A consistent model for biological membranes will emerge quickly. 

Strong support for the lipid bilayer model comes from the preparation of another type of artificial mem-... 

Lipid bilayer (see Bilayer). Model for the structure of the cell membrane based on the hydrophobic interaction between phospholipids. 

Multiplex CARS microspectroscopy, in conjunction with appropriate spectral analysis tools, was successfully applied to the study of phospholipid bilayer model systems [120, 121, 142, 70, 143], lipids within cells [144, 127, 145-147, 141], a single pollen grain [148], a single bacterial endophore [140], a molecular J-aggregate microcrystal [149], silicon components on a wafer [130], separated phases in polymer blends [123, 135], and concentration profiles in a microreactor [150]. 

Fig. 20. Composition (Fe(II) and Fe(III)) of the passive layer formed for 300 s on Fe in 1 M NaOH calculated from XPS measurements on the basis of a bilayer model including the potentiodynamic polarization curve with indication of formation of soluble Fe2+ and Fe3+ species. Hp and Epi are the passivation potentials in alkaline solution and acidic electrolytes (Flade potential) extrapolated to pH 12.9 [12],...

J m 1. However, it should not be forgotten that the % values of BLM depend on the adopted bilayer model. In that sense a comparison between the values of yi for foam bilayers and BLM might be misleading. That is why the data for foam bilayers obtained from the t(C) and W(C) dependences having yi as a free parameter, can be regarded as most reliable. 

Wiener, M. C. and White, S. H. (1991a). Fluid Bilayer Structure Determination by the Combined Use of X-ray and Neutron Diffraction. I. Fluid Bilayer Models and the limits of Resolution. Biophys. J. 59 162. 

The wide range of hydrophobe / hydrophile ratios in the cubic phase region is also Afficult to reconcile wiA a bilayer model, and in fact has never bwn observed to Ais extent in any bilayer cubic phase, but it is reaAly explained by Ae progression depicted in Hgure 4 ... 

Prenner EJ, Lewis RNAH, McElhaney RN. The interaction of the antimicrobial peptide gramicidin S with lipid bilayer model and biological membranes. Biochim. Biophys. Acta 1999 1462 201-221. Papahadjonponlos D, Moscarello M, Eylar EH, Isaac T. Effects of proteins on thermotropic phase transitions of phospholipid membranes. Biochim. Biophys. Acta 1975 401 317-335. 

Adhesion of different immune cells to one another or to epithelial cells has also been studied using planar bilayer models. For example, lymphocyte function-associated protein-1 (LFA-1) promotes cell adhesion in inflammation [i.e., a reaction that can be mimicked by binding to purified ICAM-1 in supported membranes (70)]. Similarly, purified LFA-3 reconstituted into supported bilayers mediates efficient CD2-dependent adhesion and differentiation of lymphoblasts (71). This work was followed by a study in which transmembrane domain-anchored and GPl-anchored isoforms of LFA-3 were compared (72). Because this research occurred before the introduction of polymer cushions and because the bilayers were formed by the simple vesicle fusion technique, the transmembrane domain isoform was immobile, whereas the GPl isoform was partially mobile. By comparing results with these two isoforms at different protein densities in the supported bilayer, the authors showed that diffusible proteins at a sufficient minimal density in the supported membrane were required to form strong cell adhesion contacts in this system. 

In 1980 it was pointed out that the prolamellar body is a perfect example of a Cp structure [4]. (Later, more detailed, analyses have revealed that it may also be a Cd structure cf. section 7.2.) Following work on the structure of cubic phases, it was also realised that two-dimensional analogues are possible. This in turn suggested that a phase transition involving changes in the intrinsic curvature of membranes might be possible [29, 30]. Such a mechanism has far reaching implications. Clear evidence for such transitions between bilayer conformations has been reported [9]. This membrane bilayer model will be described below. 

Figure 5. Schematic representation of (a) interdigitated model and (b) bilayer model in the zigzag morphology.

Fig. 10. Schematic diagram of a microcomputer-controlled system of nanosecond attenuated total reflection UV-visible absorption spectroscopy. Inserted figure is an optical set of the sample where a bilayer model system consists of a thin surface-film and a thick bulk-film.

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