The mitochondrion is a double membrane organelle that is involved in various biosynthetic and metabolic pathways including regulation of cell death through apoptosis. Apoptosis is a highly complex process which involved an energy-dependent cascades of molecular event. Intrinsic pathway is the apoptotic pathway which is initiated from the mitochondria. On the other hand, the pathway that involved the cell surface receptor is identified as the extrinsic pathway. The role of mitochondrion in apoptosis in the mammalian cell was emphasized when several mitochondrial proteins were identified. These proteins were discovered to be able to stimulate cellular apoptotic programmed cell death directly. The intermembrane space proteins, such as cytochrome c, Smac/DIABLO, and Omi/Htra2, involve activation of various caspases to undergo apoptosis. However, there is some that act in a caspase-independent manner, such as AIF and endonuclease G. Cytochrome c release into the cytosol is directed by the Bcl-2 family of protein following the permeabilization of the outer mitochondrial membrane, mediated by pro-apoptotic Bcl-2 family proteins. Due to the involvement of various proteins that act as mitochondrial stressors in theinduction of apoptosis, this review will emphasize the role of different stressor proteins towards this important organelle that regulate apoptosis.
