Highly sensitive protease assay using fluorescence quenching of peptide probes based on photoinduced electron transfer

Making the cut and then detecting it: Short fluorophore-labeled peptide substrates (see scheme) show strong fluorescence quenching due to electron transfer from a tryptophan residue (blue) to the dye (gray, red). Upon specific cleavage of the peptide by proteolytic enzymes, quenching is prevented and the fluorescence intensity increases. The method can be used to assay proteolytic enzymes with detection limits in the picomolar range.