FDP (fluorescein diphosphate, tetraammonium salt, high purity) is the most sensitive fluorogenic alkaline phosphatase substrate. It is also an excellent substrate for protein tyrosine phosphatase (PTPase) and thus the substrate of choice in the high throughput screening (HTS) for PTPase inhibitor. FDP itself is colorless, but the end product of the enzymatic reaction is the green fluorescent dye fluorescein.λEx/λEm = 490/514 nm (end product)ε = 90,000 (end product)Off-white solid soluble in waterStore at -20°C and protect from light, especially in solutionC20H26N4O11P2MW: 560.39[217305-49-2]