Configurational statistics of acyl chains in polyunsaturated lipid bilayers from deuterium NMR

Abstract

The gain a better understanding of the biological roles of polyunsaturated phospholipids, deuterium (/sup 2/H) NMR studies have been conducted of 1-perdeuteriopalmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine, an asymmetric or mixed-chain saturated-polyunsaturated phospholipid, in the liquid crystalline (L/sub ..cap alpha../) phase. The palmitoyl (16:0) chain at the glycerol sn-1 position was labeled with /sup 2/H by perdeuteration, whereas the polyunsaturated, docosahexaenoyl (22:6 omega 3) chain at the sn-2 position was unlabeled, i.e., protiated. The /sup 2/H NMR results were compared to studies of 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphocholine, in which both the sn-1 and sn-2 palmitoyl chains were perdeuterated, as well as 1-palmitoyl-2-perdeuteriopalmitoyl-sn-glycero-3-phosphocholine, in which only the sn-2 chain was perdeuterated. Multilamellar phospholipid dispersions containing 50 wt % H/sub 2/O were employed, and /sup 2/H NMR spectra were obtained using quadrupolar echo methods at a magnetic field strength of 8.5 T. The experimental /sup 2/H NMR spectra were numerically deconvoluted (de-Paked) to yield subspectra corresponding to the parallel bilayer orientation with respect to the main applied magnetic field. The increased resolution of the de-Paked subspectra enabled profiles of the segmental order parameters of the individual C-/sup 2/H bonds, denoted by absolute value of S/sub CD/(i), to be derived as a function of chain position. Significant differences in the /supmore » 2/H NMR spectra and derived absolute value of S/sub CD/(i) profiles of the per-/sup 2/H-16:0 chains of the polyunsaturated and saturated bilayers were found.« less