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Fusion Of Phospholipid Vesicles Arrested By Quick-Freezing. The Question Of Lipidic Particles As Intermediates In Membrane Fusion, E. L. Bearer, Nejat Düzgüneş, Daniel S. Friend, Demetrios Papahadjopoulos

All Dugoni School of Dentistry Faculty Articles

We have examined the early events in Ca2+-induced fusion of large (0.2 μm diameter) unilamellar cardiolipin/phosphatidylcholine and phosphatidylserine/phosphatidylethanolamine vesicles by quick-freezing freeze-fracture electron microscopy, eliminating the necessity of using glycerol as a cryoprotectant. Freeze-fracture replicas of vesicle suspensions frozen after 1-2 s of stimulation revealed that the majority of vesicles had already undergone membrane fusion, as evidenced by dumbbell-shaped structures and large vesicles. In the absence of glycerol, lipidic particles or the hexagonal HII phase, which have been proposed to be intermediate structures in membrane fusion, were not observed at the sites of fusion. Lipidic particles were evident in less …