Cathepsins are a class of globular lysosomal proteases playing a vital role in mammalian cellular turnover. They degrade polypeptides and are distinguished by their substrate specificities. Cathepsin G is the serine protease released by neutrophils upon their activation. Cathepsin G is currently being explored as a target for anti-inflammatory and anti-infective drugs. The SensoLyte® 520 Cathepsin G Activity Assay Kit uses a HiLyte™ Fluor 488/QXL^® 520 FRET peptide substrate for the measurement of enzyme activity. In the intact FRET peptide, the fluorescence of HiLyte™ Fluor 488 is quenched by QXL^® 520. Upon cleavage of the FRET peptide by the active enzyme, the increase of fluorescence can be continuously monitored at excitation/emission = 490/520 nm. With superior fluorescence quantum yield and longer emission wavelength, the HiLyte™ Fluor 488/QXL^® 520 based FRET peptide has less interference from the autofluorescence of test compounds and cellular components and provides better assay sensitivity. The fluorescent signal from HiLyte™ Fluor 488 is stable at low pH, which is the optimal pH for cathepsin activity. The kit can be used to detect the activity of Cathepsin G enzyme in biological samples and purified enzyme preparations. The kit contains: • HiLyte™ Fluor 488/QXL^®520-based FRET peptide substrate (Ex/Em=490/520 nm upon cleavage) • Assay buffer • Human Cathepsin G • Inhibitor • Fluorescence reference standard for calibration • A detailed protocolKit size: 100 assays (96-well plate)