In mammals, cytochrome c is part of the apoptosome complex. It binds to the core subunit, APAF1, initiating apoptosome assembly. In mammals the release of mitochondrial cytochrome c into the cytoplasm is the primary pro-apoptotic signalling event. In Drosophila, the requirement for cytochrome c (Cyt-c-d, Cyt-c-p) is not clear (FBrf0151953, FBrf0200687 and FBrf0212736).