Fluorospectroscopic studies of various ganglioside and ganglioside--lecithin dispersions. Steady-state and time-resolved fluorescence measurements with 1,6-diphenyl-1,3,5-hexatriene.

Abstract

Molecular motions of 1,6-diphenyl-1,3,5-hexatriene (DPH) in gangliosides (GM3, GM2, GM1, GD1a, and GD1b), GA1 glycosphingolipid, and dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC)--ganglioside mixed dispersions were studied by using techniques of steady-state and nano-second time resolved fluorescence measurements in the temperature range of 20--50 degrees C. The total fluorescence decay s(t) was approximated to a best-fit curve of double-exponential decays, and two fluorescence lifetimes were obtained. The values of the shorter fluorescence lifetime in dispersions composed of a single glycosphingolipid component approached those of the longer one on addition of DPPC. The molecular arrangement or microheterogeneity of the hydrocarbon region surrounding DPH molecules changed depending on the ratio of DPPC to ganglioside molecules and on the temperature. The steady-state anisotropy rs in dispersions composed of a single glycosphingolipid component exhibited smooth changes, not abrupt ones, in the temperature range, in contrast to that in DPPC liposomes. In the various glycosphingolipid dispersions studied, the motion of DPH molecules was the most restricted in the GA1 dispersion. Sialic acid linked to the neutral sugar backbone influenced the hydrophobic region and increased the motion of DPH molecules. In the gangliosides tested, the motion of DPH molecules in the hydrophobic region of GM1 ganglioside was found to be the most restricted. These comparative studies indicate that the ultimate and/or penultimate carbohydrate moieties of the neutral sugar backbone of gangliosides and the topographical difference in the locations of the sialic acid linkage influence the integrity of the membranes including the hydrophobic region.