Membranes model system

Lalchev, Z. I. and Mackie, A. R. (1999) Molecular lateral diffusion in model membrane systems. Colloid Surf. B, 15, 147-160. 

Clarke RJ, Zouni A, Holzwarth JF (1995) Voltage sensitivity of the fluorescent probe RH421 in a model membrane system. Biophys J 68 1406-1415... 

Prosser RS, Hwang JS, Void RR (1998) Magnetically aligned phospholipid bilayers with positive ordering a new model membrane system. Biophys J 74 2405-2418... 

Figure 2. Model membrane systems, (a) Monolayer at the gas-water interface, (b) Planar bimolecular lipid membrane (BLM). (c) Liposomes.

The polymerization of the butadiene monomers (3,4) can also be followed spectroscopically by the disappearance of the strong absorption of the monomers at 260 nm, whereas the absorption of the resulting poly-1,4-trans(butadiene)s is too small to be observed in a single monolayer. The polymers from the butadiene and methacryloyl lipids are probably better model membrane systems, because the polymer chains are still mobile and not excessively rigid as the polydiacetylenes. 

F. T. Hong, The bacteriorhodopsin model membrane system as a prototype molecular computing element, BioSystems, 19, 223-236 (1986). 

MD simulations of model membrane systems have provided a unique view of lipid interactions at a molecular level of resolution [21], Due to the inherent fluidity and heterogeneity in lipid membranes, computer simulation is an attractive tool. MD simulations allow us to obtain structural, dynamic, and energetic information about model lipid membranes. Comparing calculated structural properties from our simulations to experimental values, such as areas and volumes per lipid, and electron density profiles, allows validation of our models. With molecular resolution, we are able to probe lipid-lipid interactions at a level difficult to achieve experimentally. 

All four systems illustrated in Fig. 4 exhibit properties differing from those of cell membranes. Methods a-c have no influence on the head groups and preserve physical properties, such as charge, charge density, etc. The fluidity of the hydrocarbon core, however, is drastically decreased by the polymerization process. In case d, fluidity is not affected, but there is no free choice of head groups. In comparison to biomembranes, all polymerized model membrane systems will show an increase in viscosity and a decrease in lateral mobility of the molecules. 

Besides polymerization, another type of polyreaction can be used for stabilizing model membrane systems. Recently, Fukuda et al.28) described polyamide formation via polycondensation in monolayers at the gas/water interface (definition of mono-layers see Sect. 3.2). Long-chain esters of glycine and alanine were polycondensed to yield non-oriented polyamide films of polyglycine and polyalanine. 

Whether polymerized model membrane systems are too rigid for showing a phase transition strongly depends on the type of polymerizable lipid used for the preparation of the membrane. Especially in the case of diacetylenic lipids a loss of phase transi tion can be expected due to the formation of the rigid fully conjugated polymer backbone 20) (Scheme 1). This assumption is confirmed by DSC measurements with the diacetylenic sulfolipid (22). Figure 25 illustrates the phase transition behavior of (22) as a function of the polymerization time. The pure monomeric liposomes show a transition temperature of 53 °C, where they turn from the gel state into the liquid-crystalline state 24). During polymerization a decrease in phase transition enthalpy indicates a restricted mobility of the polymerized hydrocarbon core. Moreover, the phase transition eventually disappears after complete polymerization of the monomer 24). 

Ion Binding and Water Orientation in Lipid Model Membrane Systems Studied by NMR... 

Thus, 26 molecules of linoleic acid undergo autoxidation when a single free radical is introduced into this model membrane system (96). That much damage might well be enough to destroy the membrane and produce cell lysis and death however, we must remember that in the real system, the polyunsaturated fatty acids (PUFA) would be protected by antioxidants such as vitamin E. 

Hope, M. J., Wong, K. F., and Cullis, P. R. (1989), Freeze-fracture of lipids and model membrane systems, J. Electron. Microsc. Tech., 13,277-287. 

Debouzy, J.C., Aous, S., Dabouis, V., Neveux, Y., Gentilbomme, E. (2002). Phospholipid matrix as a target for sulfur mustard (HD) NMR study in model membrane systems. Cell Biol. Toxicol. 18 397-408. 

McElhaney, R. N. Differential scanning calorimetric studies of lipid-protein interactions in model membrane systems. Biochimica et Biophysica acta 564 361-421, 1986. 

The preliminary results just reported for DPPC/OA monolayers illustrate the way in which neutron reflectometry can be used to study the interaction of components in model membrane systems. In particular, the technique has been shown to be useful in the study of the water associated with lipid headgroups. Data analysis by the partial stmcture factor method offers the potential to study complex multicomponent membrane systems, which have more relevance to the behavior of biological membranes in vivo. 

In conclusion, supported bilayers have evolved into a reliable model membrane system since their first inception almost a quarter century ago. Numerous basic research questions regarding the structure and function of biological membranes and applications that range from biosensing to proteomic analyses of membrane components have been addressed with this system. We anticipate more growth and an even more prominent role of this tool in basic and applied membrane research in the decades to come. 

Tamm LK. The substrate supported lipid bilayer-a new model membrane system. Klin. Wochenschr. 1984 62 502-503. 

Single- and double-chained lipid derivatives of purines and purine nucleosides, such as 1-7, have been prepared. Ultrasonication of such compounds leads to either nucellar (single-chain compounds) or liposomal aggregates (double-chained compounds). Their surface behavior in monolayer, bilayer, and multilayer model membrane systems has been studied. 

Figure 10.5.30 Schematic Representation of Standard U-Tube-type Model Membrane System Used to Test the Anion Carrier Capability of a Given Expanded Porphyrin System (Illustrated with a Generalized Nucleotide Serving as the Putative Substrate).

Fry M, Plummer DT.The interaction of cephaloridine with model membrane systems and rat kidney lysosomes. Chem Biol Interact 1979 25(1) 113-124. 

The interaction of CNTs with membrane bilayers has been studied mainly with model membrane systems, and limited data have been obtained in vivo. Available evidence indicates that at low pH TeTx and BoNTs undergo a conformational change from a water soluble "neutral" form to an "acidic" form, the latter characterized by the exposure of hydrophobic segments. This increase in hydrophobicity allows penetration of both the H and L chains into the hydrocarbon core of the lipid bilayer (Montecucco etal., 1994). Following this low pH-induced membrane insertion, TeTx and BoNTs form ion channels in planar lipid bilayers (Beise et al., 1994 Montecucco et al., 1994). These channels are cation-selective, have few tens of pS conductance and are per-... 

Dodecyl phosphocholine micelles in solution are useful and well characterized as a model membrane system for solution NMR studies. To access the membrane-induced conformation and orientation of cardiotoxins, the interaction of the p-type cardiotoxin II from Naja oxiana snake venom with perdeuterated dodecyl phosphocholine was studied by H NMR spectroscopy and diffusion measurements.247 2D NMR is an efficient tool and has been widely used to study the interaction of dodecyl phosphocholine with peptides and protein.248-250 2D... 

Multilamellar vesicles are the most commonly used model membrane systems. It is important to note that in order to simplify the parameters of the study, in most cases the model membranes are prepared exclusively ftom phospholipids and they do not contain other molecules, usually present in biological membranes that have an important role in their fiinctionality. The complexity of real membranes is not close to the artificial model membranes and these systems, i.e. liposomes, are not an absolute analog of the biological membranes. 

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