Preparation of Cytosolic Extracts and Activation of Caspases by Cytochrome c

It can be useful to explore the caspase activation process in an in vitro setting. In this protocol, cytosolic extracts prepared from cell culture are incubated with cytochrome c and adenosine triphosphate (dATP), leading to the oligomerization of apoptotic protease activating factor-1 (APAF-1) and the formation of the apoptosome. The apoptosome serves as an activation platform for caspase-9, which binds to the apoptosome through heterodimeric caspase recruitment domain (CARD) interactions and then dimerizes. This leads to cleavage of the executioner, caspase-3. These extracts contain highly active caspases that can be analyzed using a variety of biochemical assays.