PROTON NUCLEAR-MAGNETIC-RESONANCE STUDIES ON THE MOLECULAR-DYNAMICS OF PLASMENYLCHOLINE CHOLESTEROL AND PHOSPHATIDYLCHOLINE CHOLESTEROL BILAYERS

Physiologically relevant molecular species of plasmenylcholine and phosphatidylcholine were synthesized and their molecular dynamics and interactions with cholesterol were compared by determination of salient proton spin-lattice relaxation times and apparent activation energies for H-1-NMR observable motion. The molecular dynamics of PA PhosCho (1-hexadecanoyl-2-eicosatetra-5',8',11',14'-enoyl-sn-glycero-3-phosphocholine) were substantially different from PA PlasCho (1-O-(Z)-hexadec-1'-enyl-2-eicosatetra-5',8',11',14'-enoyl-sn-glycero-3-phosphocholine) in multiple regions of the bilayer. Furthermore, the fluidity gradient of PA PhosCho was larger than that of PA PlasCho as ascertained by H-1 spin-lattice relaxation time measurements. Introduction of cholesterol into each bilayer resulted in disparate effects on the dynamics of each subclass including: (1) increased motional freedom in the polar head group of PA PlasCho without substantial alterations in the dynamics of the polar head group of PA PhosCho; and (2) increased immobilization of the membrane interior in PA PlasCho in comparison to PA PhosCho. Analysis of Arrhenius plots of T1 relaxation times demonstrated that the apparent activation energies for vinyl and bisallylic methylene proton NMR observable motion in PA PhosCho were greater than that in PA PlasCho. Thus, comparisons of spin-lattice relaxation times and apparent activation energies demonstrate that vesicles comprised of PA PlasCho and PA PhosCho possess differential molecular dynamics and distinct interactions with cholesterol. Collectively, these results underscore the significance of the conjoint presence of the vinyl ether linkage and arachidonic acid as an important determinant of membrane dynamics in specialized mammalian membranes.