The transfer of ganglioside GM1from micelles to membranes and between different membrane populations has been examined by using a pyrene fatty acid derivative of the ganglioside. The transfer of gangliosides from micelles to membranes depends on the physical state as well as the molecular composition of the acceptor vesicles. At 30 °C, the transfer of micellar gangliosides to dipalmitoylphosphatidylcholine (DPPC) large unilameller vesicles (Tm = 41.3 °C) is characterized by a rate constant of 0.01 min-1; at 48 °C, however, the rate constant is 0.11 min-1. Below the phase transition temperature, the activation energy is 25 kcal/mol whereas above the phase transition it is 17 kcal/mol. Similar experiments performed with synaptic plasma membranes yielded a rate constant of 0.05 min-1at 37 °C. The rate of transfer of ganglioside molecules, asymmetrically located on the outer layer of donor vesicles, to acceptor vesicles lacking ganglioside depends on the physical state of both the donor and acceptor vesicles. For the transfer of ganglioside from DPPC (donor) vesicles to dimyristoylphosphatidylcholine (DMPC) (acceptor) vesicles, the rates were essentially zero at 15 °C in which both vesicle populations were in the gel phase, 0.008 min-1at 30 °C in which DPPC is in the gel phase and DMPC is in the fluid phase, and 0.031 min-1at 48 °C in which both vesicle populations are in the fluid phase. The transfer of ganglioside from DPPC vesicles to synaptic plasma membranes was also dependent on the physical state of the donor vesicles and showed an inflection point at the phase transition temperature of DPPC. Finally, in the fluid phase, the addition of excess Ca2+ (20 mM) reduced the rate constant of ganglioside transfer by only 10%, in agreement with recent studies indicating that Ca2+ does not bind strongly to gangliosides.
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