In apoptosis, Apaf-1 is activated by release of which of the following substance from the mitochondria?

Apoptosis is induced by a cascade of molecular events all of the which culminate in the activation of caspases.Mitochondria contain proteins such as cytochrome c. Once released into the cytosol, cytochrome c binds to a protein called APAF-1 (apoptosis-activating factor-1), which forms a wheel-like hexamer that has been called the apoptosome. This complex activates caspase 9.