title: Cytochrome c release from mitochondria proceeds by a two-step process.
abstract: Cytochrome c is often released from mitochondria during the early stages of apoptosis, although the precise mechanisms regulating this event remain unclear. In this study, with isolated liver mitochondria, we demonstrate that cytochrome c release requires a two-step process. Because cytochrome c is present as loosely and tightly bound pools attached to the inner membrane by its association with cardiolipin, this interaction must first be disrupted to generate a soluble pool of this protein. Specifically, solubilization of cytochrome c involves a breaching of the electrostatic and/or hydrophobic affiliations that this protein usually maintains with cardiolipin. Once cytochrome c is solubilized, permeabilization of the outer mitochondrial membrane by Bax is sufficient to allow the extrusion of this protein into the extramitochondrial environment. Neither disrupting the interaction of cytochrome c with cardiolipin, nor permeabilizing the outer membrane with Bax, alone, is sufficient to trigger this protein's release. This mechanism also extends to conditions of mitochondrial permeability transition insofar as cytochrome c release is significantly depressed when the electrostatic interaction between cytochrome c and cardiolipin remains intact. Our results indicate that the release of cytochrome c involves a distinct two-step process that is undermined when either step is compromised.
authors.affiliation: Division of Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Box 210, SE-171 77 Stockholm, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Ott
authors.forename: John D
authors.initials: JD
authors.lastname: Robertson
authors.forename: Vladimir
authors.initials: V
authors.lastname: Gogvadze
authors.forename: Boris
authors.initials: B
authors.lastname: Zhivotovsky
authors.forename: Sten
authors.initials: S
authors.lastname: Orrenius
mesh_terms: D000818:Animals; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008930:Mitochondria, Liver / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D055672:Static Electricity
chemical_list: D003574:Cytochrome c Group