Effects of Ganglioside GD1a on the Fluidity and Phase Transition of Phosphatidylcholine Model Membrane Immobilized on Porous Cellulose Acetate Filter

Abstract

The thermotropic effect of ganglioside GD1a on the phosphatidylcholine membrane immobilized on the porous cellulose acetate filter was investigated by ESR spin-labeling and DSC. The spin-labeled GD1a having 12-DOXYL-stearic acid instead of the long acyl chain of the ceramide portion (GD1a^*) was incorporated into the model membrane. An ESR examination of the membrane showed that GD1a^* undergoes an anisotropic rotation in the wide range of temperature -30-70°C. By monitoring the overall splitting (2T//) of spin-labeled phosphatidylcholine (PC^*), the model membranes were found to show decreased fluidity in accordance with the GD1a content. The phase transition temperature (Tm) of distealoyl-phosphatidylcholine (DSPC) model membranes could be estimated by the measurement of ESR and DSC. The effects of GD1a were found to be more significant in broadening the phase transition rather than in elevating the Tm of DSPC model membranes.