= Solution
<NBD> and rhodamine are initially close together in the labelled vesicle <lipid bilayer>, allowing <Förster resonance energy transfer> and suppressing donor <fluorescence>. Mixing labelled <lipid bilayer> with unlabelled <lipid bilayer> dilutes the dyes, decreases energy transfer and increases the <NBD> signal.
The rise with the complementary <SNARE proteins>, but little rise with protein-free vesicles, therefore supports \b[SNARE-dependent lipid mixing]. It is consistent with <membrane fusion>, but does not by itself distinguish complete fusion from <hemifusion> or other causes of dye dilution. A separate <content mixing assay> with a leakage control would test merger of the aqueous compartments.
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