ABSTRACT
This chapter focuses on the design of Forster resonance energy transfer (FRET) based reporters for visualization and sensing of enzymatic activities in living systems. It provides detailed discussions on the important functions of some typical enzymes in both physiological and pathological conditions. The whole molecule was not fluorescent due to the FRET quenching mechanism. One most well-characterized enzyme applied in the design of FRET-based imaging systems is ß-Lactamase. Proteases, known as proteolytic enzymes, are one of the most abundant enzyme families encoded by the human genome with some active members. Serine proteases are a family of endopeptidase, which is identified by the nucleophilic serine residue located at its enzymatic site. ß-Secretase is a membrane bound aspartic protease ubiquitously expressed in the brain and pancreas tissues. Cysteine proteases involve in the intracellular protein catabolism and extracellular protein degradation. The cysteine cathepsins, which are predominantly located in endo/lysosomal vesicles, belong to the papain subfamily of cysteine proteases.
