Phospholipids, vesicle formation

Ueno, M., Tanford, C., and Reynolds, J. A. (1984). Phospholipid vesicle formation using nonionic detergents with low monomer solubility. Kinetic factors determine vesicle size and polydis-persity. Biochemistry, 3070-3076. 

Huang, C. (1969) Studies of phospholipid vesicles. Formation and physical characteristics. Biochemistry 8, 344. 

Mimms LT, Zampighi G, Nozaki Y, Tanford C, Reynolds JA. Phospholipid vesicle formation and transmembrane protein incorporation using octyl gluco-side. Biochemistry 1981 20 833. 

Modeling Pardaxin Channel. The remarkable switching of conformation in the presence of detergents or phospholipid vesicles (5) suggests that pardaxin is a very flexible molecule. This property helps to explain the apparent ability of pardaxin to insert into phospholipid bilayers. In addition, it is consistent with the suggestion that the deoxycholate-like aminoglycosteroids (5,7) present in the natural secretion from which pardaxin is purified (5) serve to stabilize its dissociated conformation. The question of the mechanism by which pardaxin assembles within membranes is important for understanding pore formation and its cytolytic activity (5). 

Biotinylated liposomes usually are created by modification of PE components with an amine-reactive biotin derivative, for example NHS-LC-Biotin (Chapter 11, Section 1). The NHS ester reacts with the primary amine of PE residues, forming an amide bond linkage (Figure 22.19). A better choice of biotinylation agent may be to use the NHS-PEG -biotin compounds (Chapter 18), because the hydrophilic PEG spacer provides better accessibility in the aqueous environment than a hydrophobic biotin spacer. Since the modification occurs at the hydrophilic end of the phospholipid molecule, after vesicle formation the biotin component protrudes out from the liposomal surface. In this configuration, the surface-immobilized biotins are able to bind (strept)avidin molecules present in the outer aqueous medium. 

Enoch, H.C., and Strittmattcr, P. (1979) Formation and properties of 100-A-diamctcr, singlebilayer phospholipid vesicles. Proc. Natl. Acad. Sci. USA 76, 145-149. 

Reeves, I.P., and Dowben, R.M. (1969) Formation and properties of thin-walled phospholipid vesicles. J. Cell Physiol. 73, 49. 

HG Enoch, P Strittmatter. Formation and properties of 1000-A-diameter, sin-gle-bilayer phospholipid vesicles. Proc Natl Acad Sci USA 76 145-149, 1979. 

Lonchin, S., Luisi, P. L., Walde, P, and Robinson, B. H. (1999). A matrix effect in mixed phospholipid/fatty acid vesicle formation. J. Phys. Chem. B, 103, 10910-16. 

By incorporating the purified electron-transport com- i plexes into phospholipid vesicles along with the mitochondrial ATP-synthase enzyme that is described below, Efraim Racker and his coworkers verified the capacity of the individual complexes I, III, and IV to support the formation of ATP. In figure 14.7, you can see that the flow... 

In this article, some of the fundamental kinetic ideas relating to spontaneous vesicle formation and breakdown by surfactants in aqueous media are described. The work is related to liposome formation and breakdown using phospholipids, and the induced rupture of membranes. 

As pointed out earlier in this article, T differs from other G proteins in that it is a peripheral membrane protein. After activation by Rho it seems to undergo subunit dissociation in which both its a subunit and its /3y complex dissociate from the Rho-containing membranes. Purification of brain G-proteins has shown that free a subunits of G0 and Gj are also water soluble, remaining in solution in the absence of detergents [74], The hydrophobicity of the whole ajSy G and Gj complexes was shown to be due to their j8y complexes 189]. Indeed, purified a subunits associate with phospholipid vesicles only if j8y complexes have been incorporated during vesicle formation [189]. Since the amino acid composition of T-/3 is equal to that of other G-j8s, but their ys differ, it follows that the principal role of y subunits should be to anchor non-T G proteins to the plasma membranes. This conclusion assumed, of course, that j8 subunits are not post-translationally modified in a tissue specific manner such that that they become water soluble in retinal photoreceptor cells and... 

Vesicles made by the methods described in the preceding questions are virtually impermeable to small cations and to most large polar molecules. They are slightly permeable to Cl, and the permeability of water is high because the solubility of water in liquid hydrocarbon is significant. When proteins are present during vesicle formation, they may be incorporated into the phospholipid bilayer. Such vesicles are known as proteoliposomes. 

Surfactants having two alkyl chains can pack in a similar manner to the phospholipids (see Box 6.4 for examples). Vesicle formation by the dialkyldimethylammonium cationic surfactants has been studied extensively. As with liposomes, sonication of the turbid solution formed when the surfactant is dispersed in water leads ultimately to the formation of optically transparent solutions which may contain single-compartment vesicles. For example, sonication of dioctadecyldimethyl-ammonium chloride for 30 s gives a turbid solution containing bilayer vesicles of 250-450 nm diameter, while sonication for 15 min produces a clear solution containing monolayer vesicles of diameter 100-150 nm. The main use of such systems has been as membrane models rather than as drug delivery vehicles because of the toxicity of ionic surfactants. 

Exposure of octadecanethiol monolayer to the small phospholipid vesicles leads to their unrolling and adsorption of a single lipid layer on top of the octadecanethiol film. Unrolling of vesicles on the surface of the hydrophilic monolayer, however, leads to the formation of the lipid bilayer on top of the original film. This principle was used by Evans and coworkers to create lipid bilayers supported by cholesterol moieties present in a mixed gold-thiol monolayer (Figure 28)430. 

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