A fluorescence assay for monitoring and analyzing fusion of biological membrane vesicles in vitro

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Abstract
A new technique has been developed to study fusion of biological membrane vesicles. Bovine chromaffin granule ghosts (CGG) were loaded with fluorescein isothiocyanate-dextran (FITC-dextran) at self-quenching concentrations. Loaded ghosts were then made to fuse with empty CGG. Fusion was induced by synexin, a protein previously proposed to be involved in exocytosis. The fusion process was monitored by measuring the dequenching of the fluorescence. Dequenching occurred as FITC-dextran was diluted into the increased volume due to fusion with empty ghosts. Spurious signals from leakage or breakage of vesicles were removed by including a specific anti-fluorescein antibody in the reaction medium. This new technique may prove to be of more general use for studying membrane fusion processes in other systems.