English: Space-fill drawing of the inactive individual subunit of the apoptosome subunit from human (Apaf-1, at left) and of the active, assembled apoptosome ring. The apoptosome subunits (shown in blue and purple) assemble when needed, to communicate between the system that signals cell death, such as cytochrome C for humans (in orange), to the system that disassembles the cell, such as the caspase proteases for humans, which are activated by binding to the CARD domains of the apoptosome (in purple). Image drawn by David Goodsell, from PDB files 3J2T, 2P1H, 1Z6T, and 3SFZ.