FIGURE 3: Models for inhibition of Bax by antiapoptotic proteins.
(A) Competition for a mitochondrial binding site. In order to permeabilize mitochondrial outer membrane, Bax needs to bind to a specific binding site in the membrane. Bcl-XL binds to the same site with higher affinity, not allowing Bax to interact with the site.
(B) Bax is constitutively targeted into mitochondrial membranes while Bcl-XL retrotrans-locates Bax back to the cytosol.
(C) Bax induces assembly of ceramide pores in the outer mitochondrial membrane and Bcl-XL disassembles these pores.
(D) Bax interacts with F1FO-ATPase to induce permeability transition that results in swelling of mitochondria and ultimately the rupture of the outer mitochondrial membrane. Bcl-XL inhibits the opening of the permeability transition pore.