Fura-2, pentaammonium salt is a ratiometric fluorescent dye that binds to free intracellular calcium. It is membrane-impermeant and may be loaded into cells via microinjection or scrape loading. A major use of Fura-2 is in drug discovery, for measuring intracellular calcium mobilization after activation of G protein-coupled receptors (GPCRs) and calcium channels. Upon calcium binding, the fluorescent excitation maximum of the indicator undergoes a blue shift from 363 nm (Ca2-free) to 335 nm (Ca2-saturated), while the fluorescence emission maximum is relatively unchanged at ~510 nm.Properties: Light yellow solid soluble in DMSO; Store at -20°C, protect from light, especially in solution; Kd: 145 nM (22°C, pH 7.2 buffer); Ex/Em = 363/512 nm, e = 27,000 M-1cm-1 (no Ca2); Ex/Em 335/505 nm, e = 35,000 M-1cm-1 (high Ca2); C29H22K5N3O14; MW: 832; [113694-64-7].