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Calcium-induced interaction of liposomes formulated of pure phosphatidylserine (PS) has been researched utilizing a rapid-mixing, rapid-freeze device. Freeze-fracture electron microscopy of this material indicated that liposomes react very rapidly after addition of calcium ions. After only 10 ms (the resolution of the technique) vesicle fusion was noticeable. At the exact time, however, vesicles also collapsed, and seemed as aggregates of flattened membranes.
The calcium-induced approach depends on calcium being added to the SUV. Fusion leads to the creation of multilamellar vesicles. LUV liposomes are created when ethylenediaminetetraacetic acid (EDTA) is added to the preparations. Only acidic phospholipids can be used in the creation of LUV liposomes.
Although Ca2+ is applied in numerous biological membrane fusion phenomena, the mechanism of its action is not well comprehended. It could participate instantly in the fusion reaction by interacting with phospholipids; it could activate particular enzymes; it could cause a conformational change in a fusogenic protein; or it could merely begin a cascade of reactions which ultimately mediate fusion.
The observation that membrane vesicles comprised of pure phospholipids can undergo fusion in the existence of Ca²+ raised the intriguing possibility that Ca²+ could mediate membrane fusion by interacting with negatively charged phospholipids in biological membranes. Since phosphatidylserine is the most large negatively charged lipid found in cell membranes, the fusion behavior of vesicles (liposomes) formulated of pure phosphatidylserine has attracted much attention. The fusion characteristics of membranes organized of zwitterionic phospholipids in conjunction with phosphatidylserine, as well as different negatively charged phospholipids, such as phosphatidate (phosphatidic acid), phosphatidylglycerol, phosphatidylinositol and cardiolipin, have been studied by numerous investigators.
Liposomes are extremely simple models of biological membranes. Yet they deliver the only applicable system to study the function of individual membrane components in a very complicated biological phenomenon, such as membrane fusion. Liposomes have been particularly helpful in the development of sensitive assays to review the kinetics of membrane fusion, since they display well-defined and reproducible fusion characteristics.
Features of our Liposomes Custom Services
Non-toxicity, biocompatible, and completely biodegradable
Boosting drug efficacy
Site avoidance effecta
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Pre-formulation, formulation feasibility and prototype development
A combination of mature preparation technologies are available
Different identification and standardization methods
Procedure optimization (experimental design) and aseptic filtration
1. Baker, P.F., and Knight, D.E., 1984, Calcium control of exocytosis in bovine adrenal medullary cells, Trends. Neurosci. 7:120–126.
2. Creutz, C.E., Zaks, w.J., Hamman, H.C. and Martin, W.H., 1987, The roles of Ca2+-dependent membrane-binding proteins in the regulation and mechanism of exocytosis, in: “Cell Fusion,” A.E. Sowers, ed., pp. 45–68, Plenum Press, New York.
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