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The distribution of the ganglioside GM1, at low concentrations, in phase-separated 1:1 dioleoyl phosphatidylcholine (DOPC)/dipalmitoylphosphatidylcholine (DPPC) Langmuir−Blodgett (LB) films transferred on mica was examined by atomic force microscopy (AFM). For concentrations below 1 mol %, GM1 distributes exclusively in the liquid-condensed DPPC phase where it forms nanometer-scale patches of round and filamentous shapes both at the boundary and toward the middle of DPPC macrodomains. Raising the GM1 concentration up to 4% increases the number of patches and creates fence like structures at the DOPC/DPPC boundary, whereas some GM1 clusters might also emerge from the liquid-expanded DOPC phase. Immiscibility of GM1 with DOPC was confirmed by examination of GM1/DOPC LB films. These data strongly support the hypothesis of the existence of GM1-enriched domains in biological membranes. They further emphasize the usefulness of the coupling of LB films with AFM detection for the investigation of complex lipid mixtures.
Vié et al. (Sat,) studied this question.