Ubiquitin 7-amido-4-methylcoumarin (Ub-AMC) is a sensitive fluorescence-based substrate of deubiquitinating enzymes. It is useful for monitoring deubiquitinating enzymes’ activity or screening inhibitors of deubiquitinating enzymes. The concentration of Ub-AMC used in deubiquitinating reactions is usually 0.1-1 μM. The released AMC fluorescence can be monitored using a fluorometer or plate reader with excitation and emission wavelengths at 360 nm and 460 nm, respectively.