5-FAM

Yellow-orange solid. Soluble in water, DMSO or DMF. The amine-reactive fluorescein derivatives are probably the most common fluorescent derivatization reagents for covalently labeling proteins. Carboxyfluorescein is better retained in cells than is fluorescein, its pKa of ~6.5 is lower than the cytosolic pH of most cells (pH ~6.8-7.4). Carboxyfluorescein is commonly employed as a polar tracer.