SURFACE CHARACTERIZATION OF PHOSPHATIDYLETHANOLAMINE CONTAINING MEMBRANES.

DISALVO, E ANIBAL; LAIRION, FABIANA; MARTINI, FLORENCIA; FRIAS, M DE LOS ANGELES; BOUCHET, ANA; DIAZ, S.B.; ALMALECK, HUGO; GORDILLO, GABRIEL

Long Beach, California

Congreso; 52 Biophysical Society; 2008

American Biophysical Society- IUPAB

Phosphatidylethanolamines is the abundant lipid component of the inner monolayer of biological membranes. It is apparently involved in specific interactions related to enzymatic processes of biological relevance. In isolated forms, unsaturated PE´s stabilizes in non lamellar phase such as the inverted hexagonal HII. In mixtures with PC´s the presence of PE determines the propensity of the membrane to abandon the bilayer structure. PE has a very low hydration (nw = 4 water molecules per lipid) in comparison to PCs (nw = 18-20 water molecules per lipid). This has been ascribed to the strong P - N interaction between lateral lipids in the solid lattice which, in turn, hinders the hydration of the phosphate. As the hydration of the lipids determines the packing and the polarization of the interphase, the presence of PE may modulate the surface properties of lipid membranes. In this regard, it is of interest to correlate the surface properties resulting from the different topological and phase states that the different PE´s may have. With this purpose, we studied by FTIR the modifications in the hydration of the phosphates groups of different PE´s in comparison to PC´s with similar chain length. The shift in the band of the antisymmetric stretching of the phosphates was correlated with the changes in the dipole potential, surface charges and area per lipid. The decrease in hydration is congruent with the decrease in area but not with the increase in the dipole potential. At similar surface pressure the interaction of an aqueous soluble protein is much lower in PE than in PC for similar hydrocarbon chains. Cyclic voltammetry experiments performed at mercury-phospholipids-water interfaces showed that under an electric perturbation, the reorientation of PC´s polar head dipoles requires less energy than PE´s. This fact indicates that lateral head group interactions are more important than hydration as a limiting factor for the reorientation of the polar heads. On the other hand, reorientation of head groups requires more energy when ester bonds are substituted by ether bonds, indicating that the hydration of the carbonyl groups originates a spacing effect which in turn, causes lower lateral interactions between polar head groups of adjacent molecules of PC´s .