Phase behavior of synthetic N-acylethanolamine phospholipids

Both saturated and unsaturated N-acylethanolamine phospholipids form lamellar structures when dispersed in buffer. The addition of excess Ca2+ (Ca2+/N-acylphosphatidylethanolamine greater than 0.5) results in precipitation. Freeze-fracture replicas indicate that the addition of Ca2+ to the unsaturated lipid results in a non-bilayer structure while the Ca2+-complex of the saturated lipid is lamellar. Since unsaturated phosphatidylethanolamine (PE) is a non-bilayer lipid, its N-acylation with a saturated fatty acid converts a non-bilayer lipid into an acidic bilayer lipid capable of interacting with Ca2+ to return to a non-bilayer structure. Ca2+ may thereby exert an influence on membrane phenomena by regulating phase behavior within certain membrane domains. Differential scanning calorimetry (DSC) indicates that N-acylation of unsaturated PE with a saturated fatty acid also results in changes in thermotropic phase behavior. Therefore, N-acylation may affect fluidity within certain membrane domains.