Msr-Ratio (Msr-green) is a ratiometric fluorescent probe of methionine sulfoxide reductase (Λex=375 nm, Λem=550 nm). Msr-Ratio is used for monitoring the enzyme activity in vitro and in live cells[1].

Msr-Ratio is converted to its corresponding sulfide form by methionine sulfoxide reductase. Msr-Ratio displays favorable properties such as a nearly 400-fold fluorescence change, fast response rate (<30 min), large Stokes shift (120 nm), and green emission (550 nm)[1].There is a very weak background signal in live HL60 cells after the addition of Msr-Ratio. As the Msr-Ratio (10 μM) incubation time increased in cells from 0 to 8 h, the fluorescence signal constantly strengthened[1].

[1]. Liangwei Zhang, et al. A ratiometric fluorescent probe of methionine sulfoxide reductase with an improved response rate and emission wavelength. Chem Commun (Camb). 2019 Jan 29;55(10):1502-1505.