Involved in the activation cascade of caspases responsible for apoptosis execution. Might function by either activating some proteins required for cell death or inactivating proteins necessary for cell survival. Heterotetramer that consists of two anti-parallel arranged heterodimers, each one formed by a small and a large subunit. Mainly expressed in peripheral blood lymphocytes, spleen and placenta. The two subunits are derived from the precursor sequence by an autocatalytic mechanism or by cleavage by Caspase-8. Belongs to the peptidase C14A family. Was originally thought to originate from human.