Bilayer-micelle transition in phosphatidylcholine-sulfatide mixtures

Sulfatides are membrane-bound glycosphingolipids which tend to associate in micellar forms in water. In this study, combining the data obtained by several techniques, including 31P-NMR, DTA calorimetry, freeze-fracture electron microscopy, trapped volume and turbidity measurements plus enzymatic determination of outer-side "marker ganglioside", have enabled us to establish that bilayered liposomes of phosphatidylcholine formed in the presence of increasing amounts of sulfatide are stable up to 30 mol % glycolipid. Above thus, bilayered lipids progressively start to break up into micellar forms with bilayer-micelle transition complete at sulfatide concentrations above 80 mol %. The gel-to-liquid-crystalline phase transition of a dipalmitoylphosphatidylcholine-sulfatide dispersion is shown to strongly influence the equilibrium between micellar and bilayered forms, the micelles being present at higher concentrations as the fluidity of the system decreases. The possibility that such structural transitions may occur in vivo and effectively contribute to the modulation of some biological properties of the membranes is discussed.