MMP-9 (gelatinase-B, collagenase-IV) is involved in quite a few diseases such as a cancer, angiogenesis, alopecia and metastasis. The SensoLyte® 520 MMP-9 Assay Kit uses a 5-FAM (fluorophore) and QXL520™ (quencher) labeled FRET peptide substrates for continuous measurement of the enzyme activities. In an intact FRETpeptide, the fluorescence of 5-FAM is quenched by QXL520™. Upon the cleavage of the FRET peptide by MMP-9, the fluorescence of 5-FAM is recovered, and can be continuously monitored at excitation/emission = 490 nm/520 nm. With superior fluorescence quantum yield and longer emission wavelength, 5-FAM/QXL520™ based FRET peptide is less interfered by the autofluorescence of test compounds and cellular components and provides better assay sensitivity. The assays are performed in a convenient 96-well or 384-well microplate format. Members of the MMP family have poor substrate sequence specificity, making it difficult to use a peptide substrate alone to differentiate the activity of a particular MMP from other MMPs. If several MMPs are coexisting in your samples and you would like to specifically measure MMP-9 activity, please choose the SensoLyte® Plus MMP-9 Assay Kit, Cat# 72017.