Disparate Molecular Dynamics of Plasmenylcholine and Phosphatidylcholine Bilayers

The molecular dynamics of binary dispersions of plasmenylcholine/cholesterol and phospha-tidylcholine/cholesterol were quantified by electron spin resonance (ESR) and deuterium magnetic resonance (²H NMR) spectroscopy. The order parameter of both 5-doxylstearate (5DS) and 16-doxylstearate (16DS) was larger in vesicles comprised of plasmenylcholine in comparison to phosphatidylcholine at all temperatures studied (e.g., = 0.592 vs. 0.487 for 5DS and 0.107 vs. 0.099 for 16DS, respectively, at 38 °C). Similarly, the order parameter of plasmenylcholine vesicles was larger than that of phosphatidylcholine vesicles utilizing either spin-labeled phosphatidylcholine or spin-labeled plasmenylcholine as probes of molecular motion. The ratio of the low-field to the midfield peak height in ESR spectra of 16-doxylstearate containing moieties (i.e., spin-labeled plasmenylcholine and phosphatidylcholine) was lower in plasmenylcholine vesicles (0.93 ± 0.01) in comparison to phosphatidylcholine vesicles (1.03 ± 0.01). ²H NMR spectroscopy demonstrated that the order parameter of plasmenylcholine was greater than that of phosphatidylcholine for one of the two diastereotopic deuterons located at the C-2 carbon of the sn-2 fatty acyl chain. The spin-lattice relaxation times for deuteriated plasmenylcholine and phosphatidylcholine in binary mixtures containing 0–50 mol % cholesterol varied nonmonotonically as a function of cholesterol concentration and were different for each phospholipid subclass. Taken together, the results indicate that the vinyl ether linkage in the proximal portion of the sn-1 aliphatic chain of plasmenylcholine has substantial effects on the molecular dynamics of membrane bilayers both locally and at sites spatially distant from the covalent alteration.