Biotin-peptide-quencher

Peptide substrate labeled with biotin and quencher... 

Protease cleaves peptide, separates quencher and biotin... 

Similar assays for measuring protease activity were also reported by Whitten and coworkers [49], These assays utilize polystyrene microspheres that are coated with streptavidin (a biotin-binding protein) and a biotinylated anionic fluorescent conjugated polyelectrolyte or a cationic polyelectrolyte, A biotinylated quencher-labeled peptide serves as a substrate for the enzyme and when mixed with the microspheres, a strong complex similar to the one in the DNA assays described in Section 13,3,1, through the biotin-avidin interaction is created [49], A schematic drawing of the assay is shown in Figure 13,7,... 

Another application of QTL probe is to monitor enzymatic activity. For example, avidin was bound to PPE-coated microspheres to monitor protease activity using a similar fluorescence tum-on method." In this assay, a peptide was modified with biotin at one end and a fluorescence quencher at the other end. The specific binding between biotin and avidin was used to bring the quencher close to the microspheres in order to quench the fluorescence of the PPL. However, in the presence of protease, the peptide was hydrolyzed, cleaving the tether, and turning on the fluorescence of the PPE. 

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