GLYCOSPHINGOLIPIDS - H-2 NMR-STUDY OF THE INFLUENCE OF CARBOHYDRATE HEADGROUP STRUCTURE ON CERAMIDE ACYL CHAIN BEHAVIOR IN GLYCOLIPID PHOSPHOLIPID-BILAYERS

Galactosyl- and glucosylceramide, globoside, and dihydrolactosylceramide, bearing [2,2-H-2(2)]stearic acid, have been studied at a concentration of 10 mol % in bilayers of dimyristoylphosphatidylcholine by H-2 NMR. The quadrupolar splittings DELTA-nu-Q of the C2 deuterons were measured at several temperatures in the range of 30-60-degrees-C. Spin-lattice relaxation times T1 of C2 deuterons were determined in the same temperature range for all lipids but globoside. T1 values at 30 and 50-degrees-C were unexpectedly short (6-8 ms), indicating reduced mobility of the ceramide acyl chains compared to that of the host phospholipid. At all temperatures, both DELTA-nu-Q and T1 were essentially identical for the monoglycosylated species, GalCer and GlcCer, indicating that the order and dynamics of the upper portion of the fatty acyl chain are insensitive to this small change in the headgroup structure. In the case of globoside, where the glycolipid headgroup is equivalent to that of GlcCer extended by three sugar residues, values for the quadrupolar splittings associated with the acyl chain C2-position were very close to those obtained for Gal- and GlcCer. In contrast, the DELTA-nu-Q values obtained for the diglycosyl species, LacCer, were significantly different at all temperatures. This different behaviour of LacCer relative to that of the other glycolipids most likely originates from an orientational change of the acyl chain at the C2-position due to the absence of a 4,5 double bond in dihydrosphingosine.T1 values for the GlcCer and GalCer systems increased with temperature, indicating that the motions responsible for relaxation were in the short correlation time regime. T1 for deuterons at the acyl chain C2-position of LacCer was observed to decrease with increasing temperature, indicating that the motion(s) dominating relaxation are in the long correlation time regime. Thus the mobility of the acyl chain at the 2-position is reduced in the LacCer with respect to GlcCer and GalCer.