The principle of DPA/Tb3 for vesicle fusion assay is based on the fact that contact of the chelator dipicolinic acid (DPA) with terbium (III) forms an instant Tb3 -DPA complex that is ~10,000 times more fluorescent than free Tb3 . In the assay, separate vesicle populations are loaded with 2.5 mM TbCl3 in 50 mM sodium citrate, or 50 mM DPA in 20 mM NaCl. Fusion of the two types of vesicles results in fluorescence increase at 490 nm or 545 nm, with excitation at276 nm (1-4). Each set of product contains 1 g terbium trichloride and 1 g DPA in two separate vials. Please also see SDIP/Europium for membrane fusion assay(#80105), which results in intense red fluorescence upon complex formation.
- λEx/λ Em(DPA/Tb3 complex) = 276/490 and 545 nm
- Store both reagents at room temperature