Cell biology 

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 at 276 nm. Each set of product contains 1 g terbium trichloride and 1 g DPA in two separate vials.

• λEx/λEm (DPA/Tb³ complex) = 276/490 and 545 nm
• DPA and Terbium are white solids and readily soluble in water
• Store both reagents at room temperature
• MWt of DPA: 167.12
• MWt. of Terbium: 265.3