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caspase Any of various enzymes that cleave target proteins during programmed cell death (see apoptosis). Caspases are formed from inactive precursors present in the cell in response to certain triggers, such as cell damage (e.g. bursting of mitochondria). They then initiate a cascade of cleavage events, possibly by liberating other ‘executioner’ enzymes, which chop up the cell's DNA, cytoskeleton, and other components.