HCV protease is identified as an important drug-screening target. The SensoLyte® 490 HCV Protease Assay Kit uses an optimized FRET peptide substrate for the continuous measurement of HCV NS3/4a activity. This FRET substrate is cleaved specifically by HCV NS3/4a protease thereby liberating the C-terminal peptide-fluorophore fragment from the proximity quenching effect of the dark quencher, resulting in a more than 10-fold increase in fluorescence. This assay can detect HCV NS3/4a protease activity at 1 pmole. The kit contains: • EDANS/DABCYL-based FRET peptide substrate (Ex/Em=340/490 nm upon cleavage) • Assay buffer • Fluorescence reference standard for calibration • A detailed protocol