CoV Protease Substrate-2 IF670 allows for efficient detection of coronavirus (CoV) proteases. This fluorescence resonance energy transfer (FRET)-based peptide substrate can be cleaved by 3C-like proteases (3CLᵖʳᵒ), the CoV main protease involved in regulating the coronavirus replication complex. 3CLᵖʳᵒ is also a potential target for therapeutic applications.

CoV Protease Substrate-2 IF670 has an excitation wavelength of 656 nm, an emission wavelength of 670 nm, an extinction coefficient of 250000 cm⁻¹ M⁻¹. It consists of a 12 amino acid sequence (VNSTLQSGLRKM) that also contains the Tide Quencher™ 5 (TQ5; quencher) and iFluor™ 670 (donor) fragments at the N- and C- termini, respectively. When the peptide substrate is intact, favorable energetic overlap of the iFluor™ 670 excited state and the TQ5 absorption leads to efficient intramolecular fluorescence quenching of iFluor™ 670 by the TQ5 fragment. Cleavage of the substrate by CoV proteases, however, dissociates the iFluor™ 670 fragment from TQ5, restoring the fluorescence of the iFluor™ 670 moiety that is directly correlated to the CoV protease activity.