The pro-apoptotic proteins, Bid and Bax, cause a limited permeabilization of the mitochondrial outer membrane that is enhanced by cytosol.
During apoptosis, an important pathway leading to caspase activation involves the release of cytochrome c from the intermembrane space of mitochondria. Using a cell-free system based on Xenopus egg extracts, we examined changes in the outer mitochondrial membrane accompanying cytochrome c efflux. The pro-apoptotic proteins, Bid and Bax, as well as factors present in Xenopus egg cytosol, each induced cytochrome c release when incubated with isolated mitochondria. These factors caused a permeabilization of the outer membrane that allowed the corelease of multiple intermembrane space proteins: cytochrome c, adenylate kinase and sulfite oxidase. The efflux process is thus nonspecific. None of the cytochrome c-releasing factors caused detectable mitochondrial swelling, arguing that matrix swelling is not required for outer membrane permeability in this system. Bid and Bax caused complete release of cytochrome c but only a limited permeabilization of the outer membrane, as measured by the accessibility of inner membrane-associated respiratory complexes III and IV to exogenously added cytochrome c. However, outer membrane permeability was strikingly increased by a macromolecular cytosolic factor, termed PEF (permeability enhancing factor). We hypothesize that PEF activity could help determine whether cells can recover from mitochondrial cytochrome c release.
Kluck
R M
RM
Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
Esposti
M D
MD
Perkins
G
G
Renken
C
C
Kuwana
T
T
Bossy-Wetzel
E
E
Goldberg
M
M
Allen
T
T
Barber
M J
MJ
Green
D R
DR
Newmeyer
D D
DD
D000263:Adenylate Kinase / Q000378:metabolism; D000408:Alamethicin / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism*; D002474:Cell-Free System; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000502:physiology; D014450:Electron Transport Complex III / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D007700:Kinetics; D008297:Male; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008930:Mitochondria, Liver / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009865:Oocytes / Q000502:physiology; D010447:Peptide Hydrolases / Q000378:metabolism; D010539:Permeability; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D014982:Xenopus laevis; D051028:bcl-2-Associated X Protein
D051023:BH3 Interacting Domain Death Agonist Protein; C494828:Bax protein, rat; C494816:Bid protein, rat; D002352:Carrier Proteins; D003574:Cytochrome c Group; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein; D000408:Alamethicin; D003576:Electron Transport Complex IV; D000263:Adenylate Kinase; D010447:Peptide Hydrolases; C108711:DEVDase; D014450:Electron Transport Complex III