BH3 death domain peptide induces cell type-selective mitochondrial outer membrane permeability

The BH3 domain is essential for the release of cytochrome e from mitochondr ia by pro-apoptotic Bcl-2 family proteins during apoptosis. This study test ed the hypothesis that a Bax peptide that includes the BH3 domain can perme abilize the mitochondrial outer membrane and release cytochrome c in the ab sence of a permeability transition at the mitochondrial inner membrane. BH3 peptide (0.1-60 muM) released cytochrome c from mitochondria in the presen ce of physiological concentrations of ions in a cell type-selective manner, whereas a BH3 peptide with a single amino acid substitution was ineffectiv e. The release of cytochrome c by BH3 peptide correlated with the presence of endogenous Bax at the mitochondria and its integral membrane insertion. Cytochrome c release was accompanied by adenylate kinase release, was not a ssociated with mitochondrial swelling or substantial loss of electrical pot ential across the inner membrane, and was unaffected by inhibitors of the p ermeability transition pore. Cytochrome c release was, however, inhibited b y Bcl-2. Although energy-coupled respiration was inhibited after the releas e of cytochrome e, mitochondria maintained membrane potential in the presen ce of ATP due to the reversal of the ATP synthase. Overall, results support the hypothesis that BH3 peptide releases cytochrome c by a Bax-dependent p rocess that is independent of the mitochondrial permeability transition por e but regulated by Bcl-2.