BAX (the BCL-2-associated X protein), a cardinal pro-apoptotic member of the BCL-2 family, is a latent, cytosolic and monomeric protein that plays an important role in the mitochondria-dependent apoptotic pathway. The nuclear magnetic resonance (NMR) spectroscopic analysis suggests that the structure of Bax consists of nine α-helices (α1 to α9) connected by short loops, in which α5, α6 and α9 are involved in the interaction of Bax with outer mitochondrial membrane (OMM). Bax remains inactive in cytosol and goes through conformational changes triggered by a cell death signal to insert, oligomerize and form large pores through the OMM with the releasing of different apoptogenic factors.