The viral genome of the SARS-CoV-2 virus encodes a main protease, 3CLpro (also called nsp5 or Mpro). The proteolytic activity of 3CLpro is needed forviral replication. This peptide substrate serves as a generic peptide substrate for 3CLpro enzymes based on the site-specific cleavage sequence for many coronavirus 3CLpro enzymes. It can be used to measure the activity of the enzyme.This is a FRET peptide where in its intact form, 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.