– Resorufin benzyl ether is a fluorometric probe that acts as a substrate for cytochrome P450 (CYP)3A4. It is typically used near its apparent Km value of 30 μM to screen the inhibition/activation potential of test compounds, to predict potential drug-drug interactions, or to monitor other CYP450 activities. Upon enzyme cleavage, resorufin benzyl ether generates a red fluorescent product (ex. 571 nm/em. 585 nm).