Apoptosis plays a major role in normal organism development, tissue homeostasis, and removal of damaged cells and is caused by the activation of proteolytic enzymes termed caspases. Proteins that comprise the Bcl-2 family such as Bax appear to control the activation of these enzymes. Bax activity was found to be regulated by its association with Bax-interacting factor 1 (BIF), a member of the endophilin B family that is associated with intracellular membranes. Following this interaction, Bax undergoes a conformational change and translocates to mitochondrial membranes. The Bax/BIF interaction appears to be enhanced by apoptotic stimuli, suggesting that BIF acts as the trigger to activate Bax, and as suppression of BIF promoted HeLa cell colony formation in soft agar, it may have a role in the suppression of cancer progression. At least two isoforms of BIF are known to exist.