| Abstract: | Deuterium wide line NMR spectroscopy was used to study cholesterol effects on the ceramide portions of two glycosphingolipids (GSLs) distributed as minor components in fluid membranes. The common existence of very long fatty acids on GSLs was taken into account by including one glycolipid species with fatty acid chain length matching that of the host matrix, and one longer by 6 carbons. N-stearoyl and N-lignoceroyl galactosyl ceramide with perdeuterated fatty acid (18:0[d35] GalCer and 24:0[d47] GalCer) were prepared by partial synthesis. They were dispersed in bilayer membranes having the 18-carbon-fatty-acid phospholipid, 1-stearoyl-2-oleoyl-phosphatidylcholine (SOPC), as major component. Glycolipid fatty acid chain behavior and arrangement were analyzed using order profiles derived from their 2H-NMR spectra. Cholesterol effects on order parameter profiles for 18:0[d35] GalCer, with chain length equal to that of the host matrix, followed the pattern known for acyl chains of phospholipids. The presence of sterol led to restriction of trans/gauche isomerization along the length of the chain, with the largest absolute increase in order parameters being toward the surface, but somewhat greater relative effect just below the "plateau" region. In cholesterol-containing membranes, order parameter profiles for the long chain species, 24:0[d47] GalCer, showed a characteristic secondary "plateau" associated with carbon atoms C14 to C23, a feature also present in SOPC bilayers without cholesterol and in pure hydrated 24:0[d47] GalCer. Cholesterol-induced ordering effects on the long chain glycolipid were similar to those described for the shorter chain species, but were minimal at the methyl terminus.(ABSTRACT TRUNCATED AT 250 WORDS) |
