Polymorphism of phosphatidylglycerol-phosphatidylethanolamine model membrane systems: a 31p NMR study.

The structural preferences of saturated and unsaturated species of phosphatidylglycerol in isolat ion and in mixed systems with unsaturated (HTT ohase) phosphatidylethanolamine have been investigated employing 31 . . . . P NMR techniques. I t is shown that equimolar (with respect to change) Ca2 + induces a " r ig id la t t i ce" (no motion) s i tuat ion in the phosphate region of the polar headgroup for a saturated species, but not for unsaturated species. Further, phosphatidylglycerol can s tab i l ize a bi layer organization in the presence of phosphatidylethanolamine which would otherwise assume the hexagonal (HII) phase, and structural bilayer-HTl transi t ions can then be triggered in these systems by the addition of Ca2 +.