N-parinaroyl glycosphingolipids: synthesis and characterization of novel fluorescent probes of membrane structure.

N-Parinaroylceramides and -glucocerebrosides were synthesized and characterized. These fluorescent glycolipids were found to be nonperturbing membrane lipid probes, which partitioned preferentially into fluid-phase phosphatidylcholine (PC) in liposomes containing both fluid and solid-phase PC. N-Parinaroylglucocerebroside, parinaroyl-PC, and free parinaric acid were used to analyze the motion and distribution of glucocerebroside and ganglioside GM1 in liposomes composed of these glycosphingolipids (GSL) and 1-stearoyl-2-oleoyl-PC (SOPC). Steady-state fluorescence anisotropy of these probes indicated that the neutral glucocerebroside formed solid-phase domains in SOPC liposomes; these domains contained little or no PC. In contrast, the negatively charged ganglioside GM1 was miscible with fluid-phase PC. Incorporation of GM1 into SOPC liposomes resulted in an increase in the transition temperature of the mixture; no transition was observed in either of the pure GSL used over the temperature range from 5 to 70 degrees C. These data indicate that the glucocerebroside probes may be specific for sphingolipid domains in mixed PC/GSL membranes.