Figure 5.

Schematic representation of membrane insertion of Bax and Bcl-X_L. In murine thymocytes, Bax is cytosolic, Bcl-2 is predominantly membrane bound, and Bcl-X_L is present in both soluble and membrane-bound forms (i). Upon induction of apoptosis by dexamethasone or γ-irradiation, virtually all the cytosolic Bcl-X_L and a significant amount of Bax becomes membrane-bound. It is not known whether Bax, in its membrane-associated state, undergoes hetero- or homodimerizations (ii). Alternatively, it is possible that Bax, Bcl-2, and Bcl-X_L in their membrane-bound states may be competing for the binding of a yet unknown protein(s) in membranes to promote either cell death or survival (iii).