Abstract
Activity-based probes (ABPs) are reactive small molecules that covalently bind to active enzymes. When tagged with a fluorophore, ABPs serve as powerful tools to investigate enzymatic activity across a wide variety of applications. In this chapter, we provide detailed methods for using fluorescent ABPs to detect the activity of caspases during the onset of apoptosis in vitro. We describe how these probes can be used to biochemically profile caspase activity in vitro using fluorescent SDS-PAGE as well as their application to imaging protease activity in live animals and tissues.