The core pathway of programmed cell death. Multiple pathways lead to the activation of the executioners of death, the caspases (reviewed in ). IAPs (inhibitors of apoptosis) have been shown to block the conversion of pro-caspases into active enzymes, and Reaper, Hid, Grim, and Diablo/Smac prevent IAPs from carrying out this protective function. Caspases can also be activated with the aid of Apaf-1, which in turn appears to be regulated by cytochrome c and dATP. The Bcl-2 family appears to function in regulating the release of pro-apoptotic components from mitochondria as well as by possibly inhibiting Apaf-1 directly. This pathway integrates knowledge gained in multiple species, showing that apoptosis appears to be regulated in a similar manner regardless of the organism. One notable exception is that the C. elegans homologs of IAPs do not appear to function in programmed cell death.