Cathepsin E is a non-lysosomal aspartic proteinase of the pepsin superfamily. It plays an important role in protein degradation, the generation of bioactive proteins, and antigen processing. Recent studies have particularly suggested that Cathepsin E is important in host defense against cancer cells and from invading microorganisms. The SensoLyte® 520 Cathepsin E Activity Assay Kit is a homogeneous assay that can be used to detect the enzyme activity in biological samples or in purified enzyme preparations. The unique long wavelength FRET substrate employed in the assay was designed to reduce the cross reactivity of Cathepsin D. A QXL^® 520/HiLyte™ Fluor 488 pair is used for optimal quenching of the intact substrate. When active Cathepsin E cleaves the FRET substrate, it results in an increase of HiLyte™ Fluor 488 fluorescence, monitored at excitation/emission = 490 nm/520 nm. The fluorescent signal from HiLyte™ Fluor 488 is stable at low pH, an optimal pH for cathepsin activity. This assay can detect as low as 2 ng/mL active Cathepsin E.The kit contains: •QXL^® 520/HiLyte™ Fluor 488-based FRET peptide substrate (Ex/Em=490/520 nm upon cleavage) • Assay buffer • Human recombinant Cathepsin E • Inhibitor • Fluorescence reference standard for calibration • A detailed protocol Kit size: 100 assays (96-well plate)

Figure 1.Inhibition of Cathepsin E activity by Pepstatin A as measured with SensoLyte® 520 Cathepsin E Assay Kit.