Formation of inverted hexagonal phase in SDPE as observed by solid-state P-31 NMR

Docosahexaenoic acid (DHA), the longest and most unsaturated fatty acid com monly found in biological membranes, is known to affect various membrane pr operties. In a variety of cell membranes, DHA is primarily incorporated in phosphatidylethanolamines, where its function remains poorly understood. In order to understand the role of DHA in influencing membrane structure, we utilize P-31 NMR spectroscopy to study the phase behavior of 1-stearoyl-2-d ocosahexaenoyl-sn-glycerophosphoethanolamine (SDPE) in comparison to 1-palm itoyl-2-oleoyl-sn-glycerophosphoethanolamine (POPE) from 20 to 50 degreesC. Spectra of SDPE phospholipids show the formation of inverted hexagonal pha se (H-II) from 20 to 50 degreesC; in contrast, POPE mutilamellar dispersion s exist in a lamellar liquid-crystalline phase (L-alpha) at the same temper atures. The ability of SDPE to adopt nonbilayer phases at a physiological t emperature may indicate its role in imparting negative curvature stress upo n the membrane and may affect local molecular organization including the fo rmation of lipid microdomains within biological membranes. (C) 2001 Academi c Press.