THE HEMIFUSION INTERMEDIATE AND ITS CONVERSION TO COMPLETE FUSION - REGULATION BY MEMBRANE-COMPOSITION

To fuse, membranes must bend. The energy of each lipid monolayer with respect to bending is minimized at the spontaneous curvature of the mo nolayer. Two lipids known to promote opposite spontaneous curvatures, lysophosphatidylcholine and arachidonic acid, were added to different sides of planar phospholipid membranes. Lysophosphatidylcholine added to the contacting monolayers of fusing membranes inhibited the hemifus ion we observed between lipid vesicles and planar membranes. In contra st, fusion pore formation depended upon the distal monolayer of the pl anar membrane; lysophosphatidylcholine promoted and arachidonic acid i nhibited. Thus, the intermediates of hemifusion and fusion pores in ph ospholipid membranes involve different membrane monolayers and may hav e opposite net curvatures. Biological fusion may proceed through simil ar intermediates.