Di-palmitoylphosphatidylcholine DPPC

Figure 5 Example of an experimental molecular order parameter profile. O, di-palmitoylphosphatidylcholine (DPPC) A, palmitoleicphosphatidylcholine (POPC) , dipalmitoylphosphatidylserine (DPPS) based bilayers X, bilayers derived from Acholeplasma laidlawii. All measurements were taken at the same reduced temperature 0 = (T - Tc)/T = 0.0605 (where = phase transition temperature).

Both aqueous organic solvent mixtures and differently charged micelles can mimic only roughly the environment of natural cell membranes. In order to analyze in more appropriate model systems possible interactions of gastrin and CCK with cell membranes and to determine their conformational states in lipid bilayers, we have recently investigated in detailed manner this aspect using liposomes. The similarity betwen liposomes and natural membranes is extensively exploited both in vitro and in vivo because of the ability of liposomes to mimic the behaviour of natural membranes. Moreover, the value of liposomes as model membrane systems derives from the fact that they can be constructed with natural constituents. In our approach, we selected as model membranes those formed with the zwitterionic lipids di-myristoylphosphatidylcholine (DMPC) and di-palmitoylphosphatidylcholine (DPPC) as these lipids constitute the major components of most cell membranes. Moreover, in order to operate with a simple system, small unilamellar vesicles (SUVs) were used, i.e. with a diameter between 25 and 250 nm as resulting by rod-type sonication or by extrusion (51). 

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