N-Myristoylated Phosphatidylethanolamine: Interfacial Behavior and Interaction with Cholesterol

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Abstract
The interfacial packing behavior of N-myristoyldimyristoylphosphatidylethanolamine (N-14:0 DMPE) and its interaction with cholesterol were characterized and compared to the behavior of dimyristoylphosphatidylethanolamine (DMPE) using an automated Langmuir type film balance. Surface pressure and surface potential were monitored as a function of lipid cross-sectional molecular area. N-14:0 DMPE exhibited two-dimensional (2D) phase transitions of a liquid-expanded to condensed nature at many temperatures in the 15−30 °C range, but isotherms showed only condensed behavior at 15 °C. The sharp decline in the surface compressional moduli upon entering the 2D-transition region is consistent with differences in the partial molar areas of coexisting liquid-expanded (chain-disordered) and condensed (chain-ordered) phases. Including Ca2+ in the subphase beneath the negatively charged N-14:0 DMPE caused a downward shift in the 2D-transition onset pressure even in the presence of 100 mM NaCl. The average dipole moments perpendicular to the lipid−water interface for N-14:0 DMPE's liquid-expanded and condensed phases were higher than those of DMPE. At surface pressures sufficiently low (0.35) and low to intermediate surface pressures (<20 mN/m) as well as the possible coexistence of relatively immiscible solid phases at higher surface pressures (e.g., 35 mN/m).

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