A novel visible range FRET probe for monitoring acid sphingomyelinase activity in living cells.

Activity of acid sphingomyelinase has been implicated in a number of diseases like acute lung injury, sepsis or metastasis of melanoma cells. Here, we present a sphingomyelinase FRET probe based on FAM/BODIPY dyes for real-time monitoring of acid sphingomyelinase. The probe gives rise to a tremendous increase in fluorescence of the fluorescein FRET donor upon cleavage and we show that this is, to a significant part, due to cleavage-associated phase transition, suggesting a more systematic consideration of such effects for future probe development. The probe allows for the first time to monitor relative sphingomyelinase activities of intact living cells by flow cytometry.