Fluorescein diphosphate tetraammonium salt

Fluorescein diphosphate tetraammonium salt (FDPA) is a fluorescent dye used to determine the presence and concentration of calcium in biological samples. FDPA is also an experimental drug that blocks calcium release from intracellular stores by binding to the ryanodine receptor. This drug has been shown to be effective against coumarin derivatives and p-nitrophenyl phosphate, which are inhibitors of the enzyme phosphatase. The linear calibration curve of FDPA was found to be linear over a wide range of concentrations, with a phase transition temperature near 40°C. Biological samples used in this assay should be stored at 4°C or lower for best results.

Ultrasensitive fluorogenic alkaline phosphatase substrate. Hydrolysis produces the green fluorescent dye, fluorescein (Ex/Em = 490/520 nm).

Fluorescein diphosphate is a colorless and nonfluorescent substrate for alkaline phosphatases, sequential alkaline phosphatase mediated hydrolysis of its two phosphate substituents yielding weakly fluorescent fluorescein monophosphate followed by strongly fluorescent fluorescein (excitation/emission ~490/514 nm).