Apoptosis - A cellular poison cupboard

Apoptotic cell death is driven by two classes of caspase — one to initiate the response and the other to carry it out. But initiator caspases can also activate death-promoting factors from the mitochondria. One of these is cytochrome c and another, the apoptosis-inducing factor, has now been identified. Both reside in the space between the inner and outer mitochondrial membranes, flagging this compartment as an important store of death factors.