ORGANIZATION OF CHOLESTERYL ESTERS IN MEMBRANES - A DEUTERIUM NUCLEAR MAGNETIC-RESONANCE STUDY

2H-NMR spectra for [3-2H1]-, [7,7-2H2]- and [2,2,4,4,6-2H5]cholesterol, and their palmitoyl esters, in multilamellar dispersions of dipalmitoylphosphatidylcholine were obtained at a sample temperature of 45.degree. C. From the observed quadrupolar splittings, and atomic coordinates for cholesteryl laurate, the orientation of the axis of rotational diffusion within the rigid steroid moiety was calculated. The location of this axis in cholesteryl palmitate is distinctly different from that in cholesterol. From the orientation of the steroid and the values calculated for the carbon-deuterium bond order parameters. SC-2H, the molecular order parameter, S.alpha., for the steroid moiety of cholesterol palmitate and of cholesterol were found. The values S.alpha. .apprxeq. 0.47 for cholesteryl palmitate and S.alpha. .apprxeq. 0.63 for cholesterol indicate that fluctuations of the rigid steroid from the axis of motional averaging are greater for cholesteryl palmitate than for cholesterol itself.