Surface lipid bilayers

Jiang, J., Skelly, P.J., Shoemaker, C.B. and Caulfield, J.P. (1996) Schistosoma mansoni the glucose transport protein SGTP4 is present in tegumental multilamellar bodies, discoid bodies and the surface lipid bilayers. Experimental Parasitology 82, 201-210. 

The structural state of membranes was studied by EPR-spectroscopy using paramagnetic spin probes [8], Rat and mice blood erythrocytes and mice EAC cells were incubated in the presence of ichfan for 45 min then, probes were inserted. The microviscosity of various membrane sites was measured on an ER 200D-SRC spectrometer (Bruker, Germany). Probe I (2.2.6.6-tetramethyl-4-capryloyl-oxypiperidine-l-oxyl) is localized mainly in the surface lipid bilayer of membrane probe II (5.6-benzo-2.2.6.6-tetramethyl-1.2.3.4-tetrahydro-y-carboline-3-oxyl) permeates into deep-located near-protein sites of the lipid bilayer. From the EPR spectra obtained, using the formula for rapidly rotating probes, the rotation correlation time... 

Protems can be physisorbed or covalently attached to mica. Another method is to innnobilise and orient them by specific binding to receptor-fiinctionalized planar lipid bilayers supported on the mica sheets [15]. These surfaces are then brought into contact in an aqueous electrolyte solution, while the pH and the ionic strength are varied. Corresponding variations in the force-versus-distance curve allow conclusions about protein confomiation and interaction to be drawn [99]. The local electrostatic potential of protein-covered surfaces can hence be detemiined with an accuracy of 5 mV. 

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... 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

It follows from the second law of thermodynamics that the optimal free energy of a hydrocarbon-water mixture is a function of both maximal enthalpy (from hydrogen bonding) and minimum entropy (maximum degrees of freedom). Thus, nonpolar molecules tend to form droplets with minimal exposed surface area, reducing the number of water molecules affected. For the same reason, in the aqueous environment of the hving cell the hydrophobic portions of biopolymers tend to be buried inside the structure of the molecule, or within a lipid bilayer, minimizing contact with water. 

Figure 41-7. The fluid mosaic model of membrane structure. The membrane consists of a bimolecu-lar lipid layer with proteins inserted in it or bound to either surface. Integral membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and are called transmembrane proteins, while others are embedded in either the outer or inner leaflet of the lipid bilayer. Loosely bound to the outer or inner surface of the membrane are the peripheral proteins. Many of the proteins and lipids have externally exposed oligosaccharide chains. (Reproduced, with permission, from Junqueira LC, Carneiro J Basic Histology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

Cell membranes consist of two layers of oriented lipid molecules (lipid bilayer membranes). The molecules of these two layers have their hydrocarbon tails toward each other, while the hydrophilic heads are outside (Fig. 30.1a). The mean distance between lipid heads is 5 to 6mn. Various protein molecules having a size commensurate with layer thickness float in the lipid layer. Part of the protein molecules are located on the surface of the lipid layer others thread through the layer (Fig. 30.1fc). Thus, the membrane as a whole is heterogeneous and has a mosaic structure. 

The artificial lipid bilayer is often prepared via the vesicle-fusion method [8]. In the vesicle fusion process, immersing a solid substrate in a vesicle dispersion solution induces adsorption and rupture of the vesicles on the substrate, which yields a planar and continuous lipid bilayer structure (Figure 13.1) [9]. The Langmuir-Blodgett transfer process is also a useful method [10]. These artificial lipid bilayers can support various biomolecules [11-16]. However, we have to take care because some transmembrane proteins incorporated in these artificial lipid bilayers interact directly with the substrate surface due to a lack of sufficient space between the bilayer and the substrate. This alters the native properties of the proteins and prohibits free diffusion in the lipid bilayer [17[. To avoid this undesirable situation, polymer-supported bilayers [7, 18, 19] or tethered bilayers [20, 21] are used. 

In addition to the self-spreading lipid bilayer, it was also found that a lipid mono-layer showed similar spreading behavior on a hydrophobic surface (Figure 13.6) [51]. By fabricating an appropriate hydrophobic surface pattern, the spreading area and direction can be easily controlled. For both the self-spreading bilayer and monolayer, non-biased molecular transportation is an important key concept for the next generation of microfiuidic devices. 

Munro, J. C. and Frank, C. W. (2004) Insitu formation and characterization of poly (ethylene glycol)-supported lipid bilayers on gold surfaces. Langmuir, 20, 10567-10575. 

Radler. J., Strey, H. and Sackmann, E. (1995) Phenomenology and kinetics of lipid bilayer spreading on hydrophilic surfaces. Langmuir, 11, 4539-4548. 

Nabika, H., Sasaki, A.,Takimoto, B., Sawai, Y, He, S. and Murakoshi, K. (2005) Controlling molecular diffusion in selfspreading lipid bilayer using periodic array of ultra-small metallic architecture on solid surface. J. Am. Chem. Soc., 127, 16786-16787. 

Nabika, H., Takimoto, B., lijima, N. and Murakoshi, K (2008) Observation of self spreading lipid bilayer on hydrophilic surface with a periodic array of metallic nano-gate. Electrochim. Acta, 53, 6278-6283. 

FIG. 13 A schematic illustration of the effects of the free surface area of lipid bilayer membranes on the permeation of two permeants with the same molecular volume, but different cross-sectional areas, (a) A lower free surface area, (b) A higher free surface area. 

Our knowledge of biological membrane ultrastructure has increased considerably over the years as a result of rapid advances in instrumentation. Although there is still controversy over the most correct biological membrane model, the concept of membrane structure presented by Davson and Danielli of a lipid bilayer is perhaps the one best accepted [12,13]. The most current version of that basic model, illustrated in Fig. 7, is referred to as the fluid mosaic model of membrane structure. This model is consistent with what we have learned about the existence of specific ion channels and receptors within and along surface membranes. 

Fig. 7 Diagrammatic representation of the fluid mosaic model of the cell membrane. The basic structure of the membrane is that of a lipid bilayer in which the lipid portion (long tails) points inward and the polar portion (round head ) points outward. The membrane is penenetrated by transmembrane (or integral) proteins. Attached to the surface of the membrane are peripheral proteins (inner surface) and carbohydrates that bind to lipid and protein molecules (outer surface). (Modified from Ref. 14.)...

Gorter and Grendel in 1925 [527], drawing on the work of Langmuir, extracted lipids from RBC ghosts and formed monolayers. They discovered that the area of the monolayer was twice that of the calculated membrane surface of intact RBC, indicating the presence of a bilayer. This was the birth of the concept of a lipid bilayer as the fundamental structure of cell membranes (Fig. 7.1). 

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