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The stoichiometry of cytochrome c to Apaf-1 within the complex is proved to be 1:1. [1] There are some debates about whether stable incorporation of cytochrome c into the apoptosome is required following oligomerization, but recent structural data favor the idea that cytochrome c stabilizes the oligomeric human apoptosome. [1]
Cytochrome c is a highly conserved protein across the spectrum of eukaryotic species, found in plants, animals, fungi, and many unicellular organisms. This, along with its small size (molecular weight about 12,000 daltons), [7] makes it useful in studies of cladistics. [8] Cytochrome c has been studied for the glimpse it gives into evolutionary ...
Upon binding cytochrome c and dATP, this protein forms an oligomeric apoptosome. The apoptosome binds and cleaves Procaspase-9 protein, releasing its mature, activated form. The precise mechanism for this reaction is still debated though work published by Guy Salvesen suggests that the apoptosome may induce caspase-9 dimerization and subsequent ...
The X-linked inhibitor of apoptosis protein is overexpressed in cells of the H460 cell line. XIAPs bind to the processed form of caspase-9 and suppress the activity of apoptotic activator cytochrome c, therefore overexpression leads to a decrease in the number of proapoptotic agonists. As a consequence, the balance of anti-apoptotic and ...
Depending on their function, once activated, Bcl-2 proteins either promote the release of these factors, or keep them sequestered in the mitochondria. Whereas the activated pro-apoptotic Bak and/or Bax would form MAC and mediate the release of cytochrome c, the anti-apoptotic Bcl-2 would block it, possibly through inhibition of Bax and/or Bak. [18]
Caspase-9 belongs to a family of caspases, cysteine-aspartic proteases involved in apoptosis and cytokine signalling. [8] Apoptotic signals cause the release of cytochrome c from mitochondria and activation of apaf-1 , which then cleaves the pro-enzyme of caspase-9 into the active dimer form. [6]
The anti-apoptotic Bcl-2 and Bcl-xL proteins inhibit cytochrome c release through the mitochondrial pore and also inhibit activation of the cytoplasmic caspase cascade by cytochrome c. [8] Dephosphorylated BAD forms a heterodimer with Bcl-2 and Bcl-xL, inactivating them and thus allowing Bax/Bak-triggered apoptosis.
The redox potential for cytochrome c can also be "fine-tuned" by small changes in protein structure and solvent interaction. [4] The number of heme C units bound to a holoprotein is highly variable. For vertebrate cells one heme C per protein is the rule but for bacteria this number is often 2, 4, 5, 6 or even 16 heme C groups per holoprotein.