6-FAM

Yellow solid. Soluble in DMSO or water (pH ? 5). 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.