FLUID OR GEL PHASE LIPID BILAYERS TO STUDY PEPTIDE MEMBRANE INTERACTIONS

Since many studies on peptide-membrane interactions are carried out on ly with fluid phase lipid bilayers (L(alpha)-phase, absence of cholest erol) we have investigated whether this phase is really a suitable mod el for biological membranes. For this purpose the action of melittin o n zwitterionic and negatively charged phospholipid bilayers, in the ab sence and presence of 30 mol% cholesterol, was investigated by solid s tate P-31-NMR. From the NMR point of view, it appears that systems com posed of a single phospholipid best mimic the sterol-containing system a few degrees below the gel-to-fluid phase transition, i.e., in the r ippled phase (P-beta'). It is then proposed that a relatively rigid me mbrane containing local defects, rather than a L(alpha)-bilayer, is re quired as an appropriate model for natural membranes when probing the action of melittin. Such requirements might bt crucial when studying p eptide-lipid interactions.