| Abstract
| - The distribution of phosphatidylethanolamine (PE) and phosphatydilserine(PS) in liposomes wasstudied as a function of aminophospholipid concentration usingfluorescamine as labeling reagent.The method is suitable for such determination since, in the assayconditions, fluorescamine does notpenetrate the vesicles nor does it disrupt them. The liposomeswere obtained by sonication, extrusion,or mechanical dispersion (MLV). For any kind of vesicle, thepercentage of PS in the externalmonolayer is higher than that obtained for PE in the correspondingvesicles. In extruded PS liposomes,this aminophospholipid is located preferentially in the outer layer,while for PE liposomes thelocalization depends on the size of vesicle. Sonicated liposomespresent an asymmetrical distributionof both aminophospholipids, and the external location of PS or PEalways predominates. In contrast,in MLV, aminophospholipids are mainly found in the inner layers of thevesicles, except for liposomesformed by the lowest PS proportion. A remarkable feature of PSliposomes is the reduction of vesiclesize, especially in MLV liposomes, in comparison with neutralliposomes.
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