Spontaneous Transfer of Ganglioside GM₁between Phospholipid Vesicles

The transfer kinetics of the negatively charged glycosphingolipid II₃-N-acetylneuraminosyl-gangliotetraosylceramide (GM₁) were investigated by monitoring tritiated GM₁movement between donor and acceptor vesicles. After appropriate inCubation times at 45 °C, donor and acceptor vesicles were separated by molecular sieve chromatography. Donors were small unilamellar vesicles produced by sonication, whereas acceptors were large unilamellar vesicles produced by either fusion or ethanol injection. Initial GM₁transfer to acceptors followed first-order kinetics with a half-time of about 40 h assuming that GM₁is present in equal mole fractions in the exterior and interior surfaces of the donor vesicle bilayer and that no glycolipid flip-flop occurs. GM_1nettransfer was calculated relative to that of [₁₄C]cholesteryl oleate, which served as a nontransferable marker in the donor vesicles. Factors affecting the GM₁interbilayer transfer rate included phospholipid matrix composition, initial GM₁concentration in donor vesicles, and the GM₁distribution in donor vesicles with respect to total lipid symmetry. The findings provide evidence that GM₁ is molecularly dispersed at low concentrations within liquid-crystalline phospholipid bilayers.