Biophysical studies of membrane proteins/peptides. Interaction with ...
Biophysical studies of membrane proteins/peptides. Interaction with ...
Biophysical studies of membrane proteins/peptides. Interaction with ...
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drying into a film and ressuspension in an aqueous environment. Suspensions <strong>of</strong><br />
liposomes prepared in this manner are composed by concentric bilayers or multilamellar<br />
vesicles (MLV’s). Due to this arrangement <strong>of</strong> the lipid vesicles, most <strong>of</strong> the lipid bilayer<br />
surface is buried inside the liposome, as only about 10 % is found in the outside surface<br />
(Yeagle, 1993). The application <strong>of</strong> MLV´s in photophysical <strong>studies</strong> can result in several<br />
difficulties. Due to the size <strong>of</strong> the MLV’s particles, scattering is very significant and for<br />
these reason, MLV´s are seldom used.<br />
There are different strategies for obtaining unilamellar liposomes. By applying<br />
ultrasonic power to suspensions <strong>of</strong> liposomes, unilamellar vesicles <strong>of</strong> small diameter<br />
(~30 Å), also called small unilamellar vesicle (SUV) are obtained. Due to the smaller<br />
size <strong>of</strong> the particles, scattering in suspensions <strong>of</strong> SUV’s is drastically reduced, however<br />
the curvature <strong>of</strong> SUV’s is much higher than the curvature <strong>of</strong> cell <strong>membrane</strong>s, resulting<br />
in poor mimics <strong>of</strong> the properties <strong>of</strong> bio<strong>membrane</strong>s.<br />
Larger unilamellar vesicles (LUV’s) can be produced either by dialysis <strong>of</strong><br />
detergents, reverse phase evaporation, or fast extrusion through polycarbonate filters.<br />
The latter method is particularly useful due to the shorter times required when compared<br />
to the other ones, e.g., dialysis <strong>of</strong> detergents can take several days for efficient removal<br />
<strong>of</strong> detergent from liposomes (for a review, see Gennis, 1989).<br />
Much larger unilamellar vesicles (up to 300 µm) can also be prepared by gentle<br />
hydration and electr<strong>of</strong>ormation (Rodriguez et al., 2005). These vesicles are also known<br />
as giant unilamellar vesicles or GUV’s and are particularly suitable for microscopy<br />
applications as their size enables visualization and micromanipulation.<br />
Still, other types <strong>of</strong> <strong>membrane</strong> model systems exist. Lipid monolayers in water-air<br />
interface allow the study <strong>of</strong> the effect <strong>of</strong> the lateral surface pressure on <strong>membrane</strong><br />
components and on the interactions between them. Black Lipid Membranes have also<br />
proven valuable in the study <strong>of</strong> electrical properties (Yeagle, 1993).<br />
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