A Ratiometric Fluorescent Probe for Imaging of the Activity of Methionine Sulfoxide Reductase A in Cells

Abstract Methionine sulfoxide reductase A (MsrA) is an enzyme involved in redox balance and signaling, and its aberrant activity is implicated in a number of diseases (for example, Alzheimer's disease and cancer). Since there is no simple small molecule tool to monitor MsrA activity in real time in vivo, we aimed at developing one. We have designed a BODIPY‐based probe called ( S )‐Sulfox‐1, which is equipped with a reactive sulfoxide moiety. Upon reduction with a model MsrA ( E. coli ), it exhibits a bathochromic shift in the fluorescence maximum. This feature was utilized for the real‐time ratiometric fluorescent imaging of MsrA activity in E. coli cells. Significantly, our probe is capable of capturing natural variations of the enzyme activity in vivo.