RIPPLE PHASE IN ASYMMETRIC UNILAMELLAR BILAYERS WITH SATURATED AND UNSATURATED PHOSPHOLIPIDS

In a solution of phosphate-buffered saline (PBS), unilamellar bilayers with saturated phosphatidylcholines in one leaflet and negatively cha rged, unsaturated phospholipids in the other leaflet were observed in the ripple phase at room temperature using atomic force microscopy (AF M). This is the first observation of the ripple phase in asymmetric bi layers. Sodium and phosphate, components of PBS, were found to be nece ssary for the formation of the ripple structure in the asymmetric bila yers composed of dipalmitoylphosphatitdylcholine (DPPC) and 1-palmitoy l-2-oleoylphosphatidyglycerol (POPG), demonstrating a dependency for s pecific ions for this phase. These results indicate that the two leafl ets of a bilayer are closely coupled to give rise to such a long range and complicated morphology.