Enzyme activity was quantified by fluorescence kit using a specific anti-MMP-9 monoclonal antibody and a fluorogenic substrate (SensoLyte Plus 520 MMP-9 Assay Kit; AnaSpec, Inc., Fremont, CA, USA), as described previously.29 (link) MMP-9 induced cleavage of the fluorogenic peptide was measured at 490 nm excitation and 520 nm emission wavelengths.