Fig. 10. A schematic showing the dynamic relationship between Bax-Bak redistribution and the release of Cyt c and Smac from mitochondria during apoptosis. There are four distinct stages of Bax-Bak distribution in an apoptotic cell. (Stage I) Before an apoptotic stress signal is activated, Bax is diffusely distributed in the cytosol, whereas Bak is localized at the MOM. (Stage II) After the stress signal is activated, Bax starts to translocate to mitochondria and distributes evenly at the MOM, whereas Cyt c and Smac remain in the mitochondria. (Stage III) Within a few minutes, Bax and Bak begin to form small complexes at the MOM by lateral diffusion along the mitochondrial membrane. Cyt c and Smac can now be released from mitochondria through the Bax-Bak complex. (Stage IV) The Bax-Bak complexes expand to form large clusters by recruiting additional Bax and Bak molecules.