Vesicle lipid

Lipid vesicles (also known as liposomes) are spherical membrane shells of lipid bilayer in solution. You could think of them as a bubble with water inside and out. Vesicles are stable with aqueous solutions on either side of the membrane provided the osmotic difference between the two solutions is not too large. Vesicles can be large or small, multilamellar or unilamellar and provide us with a useful experimental tool. In biotechnology, liposomes are widely used to encapsulate specific molecules and can provide a mechanism for drug delivery with a targeted or slow release. 

GUVs can be observed with bright-held microscopy, although they are difficult to see because the single bilayer is only about 6 nm thick. Visualization can be greatly enhanced by the use of either phase contrast or DIG (differential interference contrast) microscopy or fluorescence microscopy if a fluorescent molecule probe can be incorporated into the lipid bilayer. 

FIGURE 6.14 A fluorescence microscope image of giant unilamellar vesicles (GUVs) in water. These vesicles were prepared from the lipid DOPC (l,2-dioleoyl-sn-glycero-3-phosphocholine) and visualized by including a small proportion of fluorescent lipid in the bilayer ( 0.05 mol%). 

FIGURE 6.15 A schematic demonstrating the electroformation method for giant unilamellar vesicle (GUV) preparation. Dry lipid films are rehydrated in the presence of an alternating electric field. ITO, indium tin oxide. 

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When Mitchell first described his chemiosmotic hypothesis in 1961, little evidence existed to support it, and it was met with considerable skepticism by the scientific community. Eventually, however, considerable evidence accumulated to support this model. It is now clear that the electron transport chain generates a proton gradient, and careful measurements have shown that ATP is synthesized when a pH gradient is applied to mitochondria that cannot carry out electron transport. Even more relevant is a simple but crucial experiment reported in 1974 by Efraim Racker and Walther Stoeckenius, which provided specific confirmation of the Mitchell hypothesis. In this experiment, the bovine mitochondrial ATP synthasereconstituted in simple lipid vesicles with bac-teriorhodopsin, a light-driven proton pump from Halobaeterium halobium. As shown in Eigure 21.28, upon illumination, bacteriorhodopsin pumped protons... 

In summary, these recently obtained results demonstrate that certain amphi-pathic peptoid sequences designed to mimic both the helical structure and approximate length of magainin helices are also capable of selective and biomimetic antibacterial activity. These antibacterial peptoids are helical in both aqueous buffer and in the presence of lipid vesicles. Ineffective (non-antibacterial) peptoids exhibit weak, random coil-like CD, with no spectral intensification in the presence of lipid vesicles. Selective peptoids exhibit stronger CD signals in bacterial-mimetic vesicles than in mammalian-mimetic vesicles. Non-selective peptoids exhibit intensely helical CD in both types of vesicles. 

Grliner, S. M., Lenk, R. P., Janoff, A. S., and Ostro, M. J. (1985). Novel multilayered lipid vesicles Comparison of physical characteristics of multilamellar liposomes and stable plurilamellar vesicles, Biochemistry. 24. 2833-2842. 

D. (1978). Effect of lipid vesicle (liposome) encapsulation of methotrexate on its chemotherapeutic efficacy in solid rodent tumors. Cancer Res., 38, 2848-2853. 

Choleate lipid cylinders Formation by fusion of unilamellar lipid vesicles, Biochim. Biophys. Acta. 394, 483-491. 

Rhoden, V., and Goldin, S. M. (1979). Formation of unilamellar lipid vesicles of controllable dimensions by detergent dialysis. Biochemistry, 18, 4173-4176. 

Szoka, F., and Papahadjopoulos, D. (1980). Comparative properties and methods of preparation of lipid vesicles (liposomes), Ann. 

The Jing group investigated their poly(L-lysine)-6-poly(L-phenylalanine) vesicles for the development of synthetic blood, since PEG-lipid vesicles were previously used to encapsulate hemoglobin to protect it from oxidation and to increase circulation time. They extended this concept and demonstrated that functional hemoglobin could be encapsulated into their vesicles. The same polypeptide material was also used to complex DNA, which caused the vesicles to lose their... 

Liposomes — These are synthetic lipid vesicles consisting of one or more phospholipid bilayers they resemble cell membranes and can incorporate various active molecules. Liposomes are spherical, range in size from 0.1 to 500 pm, and are thermodynamically unstable. They are built from hydrated thin lipid films that become fluid and form spontaneously multilameUar vesicles (MLVs). Using soni-cation, freeze-thaw cycles, or mechanical energy (extrusion), MLVs are converted to small unilamellar vesicles (SUVs) with diameters in the range of 15 to 50 nm. ... 

The availability of the purified transporter in large quantity has enabled investigation of its secondary structure by biophysical techniques. Comparison of the circular dichroism (CD) spectrum of the transporter in lipid vesicles with the CD spectra of water-soluble proteins of known structure indicated the presence of approximately 82% a-helix, 10% ) -turns and 8% other random coil structure [97]. No / -sheet structure was detected either in this study or in a study of the protein by the same group using polarized Fourier transform infrared (FTIR) spectroscopy [98]. In our laboratory FTIR spectroscopy of the transporter has similarly revealed that... 

A prominent example here are photocatalytic systems based on lipid vesicles for watersplitting into H2 and O2. Design of such systems is based on both functional and structural mimicing of natural photosynthesis. 

An attractive way to overcome this problem is to use microheterogeneous photocatalytic systems based on lipid vesicles, i.e. microscopic spherical particles formed by closed lipid or surfactant bilayer membranes (Fig. 1) across which it is possible to perform vectorial photocatalytic electron transfer (PET). This leads to generation of energy-rich one-electron reductant A" and oxidant D, separated by the membrane and, thus, unable to recombine. As a result of such PET reactions, the energy of photons is converted to the chemical energy of spatially separated one electron reductant tmd oxidant. 

Fig.3. Mechanism of PET across a lipid membrane, coupled with H2 evolution in EDTA-Ru(bipy) j -V -Pd / lipid vesicle system.

The membrane-bound catalyst for water oxidation to O2 can be prepared via oxidation of Mn(Il) and Co(ll) salts to Mn(IV) and Co(Ill) hydroxides, respectively, in the presence of lipid vesicles. Using these catalysts and photogenerated Ru(bipy)j complex as an oxidant, it is possible to oxidize water to O2 in vesicle systems. One of such systems for O2 evolution is schematically represented in Fig. 4. 

Fig.4. Photocatalytic S O -Ru(bipy) -- (OH)x -Co0(3 .,y2 lipid vesicle system for O2 evolution.

Kramer, S. D., Wunderli-Allenspach, H. The pH-dependence in the partitioning behaviour of (JlS)-[ H]propranolol between MDCK cell lipid vesicles and buffer. Pharm. Res. 1996, 13,... 

Capillary electrophoresis (CE) (see Section 3.5) has been used to determine partition coefficients [320-322]. Lipid vesicles or micelles are added to the buffer whose pH is adjusted to different values. Since drug molecules partition to a different extent as a function of pH, the analysis of mobility vs pH data yields log P values. 

An additional (electrostatic) shift occurs if the lipid vesicles or micelles have a charged surface, according to the expression suitable for monoprotic acids and bases... 

Yang, Q. Lundahl, P., Binding of lysozyme on the surface of entrapped phosphati-dylserine-phosphatidylcholine vesicles and an example of high-performance lipid vesicle surface chromatography, J. Chromatogr. 512, 377-386 (1990). 

The second model of a biological membrane is the liposome (lipid vesicle), formed by dispersing a lipid in an aqueous solution by sonication. In this way, small liposomes with a single BLM are formed (Fig. 6.11), with a diameter of about 50 nm. Electrochemical measurements cannot be carried out directly on liposomes because of their small dimensions. After addition of a lipid-soluble ion (such as the tetraphenylphosphonium ion) to the bathing solution, however, its distribution between this solution and the liposome is measured, yielding the membrane potential according to Eq. 

Liposomes, also known as lipid vesicles, are aqueous compartments enclosed by lipid bilayer membranes [56,57]. Figure 10.11 shows how lipid bilayers are arranged in the liposome and the lipid structures in large unilamellar vesicles and multilamellar vesicles. Lipids consist of two components ... 

The squaraine probe 9g was tested for its sensitivity to trace the formation of protein-lipid complexes [57]. The binding of dye 9g to model membranes composed of zwitter-ionic lipid phosphatidylcholine (PC) and its mixtures with anionic lipid cardiolipin (CL) in different molar ratios was found to be controlled mainly by hydrophobic interactions. Lysozyme (Lz) and ribonuclease A (RNase) influenced the association of 9g with lipid vesicles. The magnitude of this effect was much higher... 

Sen P, Satoh T, Bhattacharyya K, Tominaga K (2005) Excitation wavelength dependence of solvation dynamics of coumarin 480 in a lipid vesicle. Chem Phys Lett 411(4—6) 339-344... 

Kleinfeld, A.M., Chu, P. and Storch, J. (1997) Flip-flop is slow and rate-limiting for the movement of long chain anthroyloxy fatty acids across lipid vesicles. 

Other investigators have shown that the informational molecules of Life - RNA and DNA - themselves can be synthesized within lipid vesicles. 

All of the above-mentioned examples describe organosiloxane hybrid sheet-like structures. However, cell-mimicry requires spherical structures that can form an inner space as a container. Liposomes and lipid bilayer vesicles are known as models of a spherical cell membrane, which is a direct mimic of a unicellular membrane. However, the limited mechanical stability of conventional lipid vesicles is often disadvantageous for some kinds of practical application. 

Khramov, M.I. and Parmon, V.N. (1993) Synthesis of ultrafine particles of transition-metal sulfides in the cavities of lipid vesicles and the light-stimulated transmembrane electron-transfer catalyzed by these particles. Journal of Photochemistry and Photobiology A-Chemistry, 71, 279-284. 

Use of encapsulated labeled precursors in lipid vesicles enabled the Hawaiian group to conduct the biosynthetic studies - with the exception of workup of the sponge - entirely in the field. Incorporation of doubly labeled [13C, 15N]cyanide into a Ciocalypta sp. and an Acanthella sp. produced labeled 9-isocyanoneopupukeanane (77) and kalihinol-F (112) respectively [71]. Detection of incorporation was followed by 13C NMR experiments. 

Liposome conjugates may be used in various immunoassay procedures. The lipid vesicle can provide a multivalent surface to accommodate numerous antigen-antibody interactions and thus increase the sensitivity of an assay. At the same time, it can function as a vessel to carry encapsulated detection components needed for the assay system. This type of enzyme-linked immunosorbent assay (ELISA) is called a liposome immunosorbent assay or LISA. One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin-avidin or biotin-streptavidin complexes. The avidin-biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 23) (Savage et al., 1992). 

H.S. Jung, J.M. Kim, J.W. Park, H.Y. Lee, and T. Kawai, Amperometric immunosensor for direct detection based upon functional lipid vesicles immobilized on nanowell array electrode. Langmuir 21, 6025-6029 (2005). 

Quevillon-Cheruel S, Leulliot N, Acosta Muniz C, Vincent M, Gallay J, Argentini M, Cornu D, Boccard F, Lemaitre B and van Tilbeurgh H. 2009. EVF, a virulence factor produced by the Drosophila pathogen Erwinia carotovora is a S-palmitoylated protein with a new fold that binds to lipid vesicles. J Biol Chem. 284(6) 3552-3562. 

Cell membranes or synthetic lipid vesicles with normal low permeability to water will, if reconstituted with AQP1, absorb water, swell and burst upon exposure to hypo-osmotic solutions. The water permeability of membranes containing AQP 1 can be about 100 times greater than that of membranes without aquaporins. The water permeability conferred by AQP1 (about 3 billion water molecules per subunit per second) is reversibly inhibited by Hg2+, exhibits low activation energy and is not accompanied by ionic currents or translocation of any other solutes, ions or protons. Thus, the movement of water through aquaporins is an example of facilitated diffusion, in this case driven by osmotic gradients. 

A first approach to study the interaction of posttranslational modified Ras proteins with membranes was the analysis of binding and exchange of isoprenyl-ated peptides with and between lipid vesicles utilizing a fluorescent bimanyl label. Studies with K-Ras peptides revealed that a single isoprenyl group is sufficient for membrane association only if supported by carboxymethylation of the C-terminal cysteine [227,228]. 

As well as fluorescence-based assays, artificial membranes on the surface of biosensors offered new tools for the study of lipopeptides. In a commercial BIA-core system [231] a hydrophobic SPR sensor with an alkane thiol surface was incubated with vesicles of defined size distribution generating a hybrid membrane by fusion of the lipid vesicles with the alkane thiol layer [232]. If the vesicles contain biotinylated lipopeptides their membrane anchoring can be analyzed by incubation with streptavidine. Accordingly, experiments with lipopeptides representing the C-terminal sequence of N-Ras show clear differences between single and double hydrophobic modified peptides in their ability to persist in the lipid layer [233]. 

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