The signaling process by either the extrinsic or intrinsic pathway involves the activation of caspases.
Caspases are cysteine proteases that cleave their substrates on the carboxyl side of aspartic acid
residues. Their role as central executioner of cell death has been amply documented in the last
decade5 and is supported by the evidence that caspases seem to be evolutionarily conserved, being
identified in Drosophila melanogaster, Caenorhabditis elegans, and Xenopus laevis, as well as in
mammals.