To elucidate the mechanism of activation of procaspase-9 by Apaf-1, we produced
recombinant full-length Apaf-1 and purified it to complete homogeneity. Here we show using
gel filtration that full-length Apaf-1 exists as a monomer that can be transformed to an
oligomeric complex made of at least eight subunits after binding to cytochrome c and dATP.
Apaf-1 binds to cytochromec in the absence of dATP but does not form the oligomeric
complex. However, when dATP is added to the cytochromec-bound Apaf-1 complex …