Catalysis of the reaction: 4 H+ + 15-cis-4,4'-diapophytoene + 4 FAD = 4,4'-diapolycopene + 4 FADH2. This reaction consists of four successive dehydrogenations that lead to the introduction of three double bonds into 4,4'-diapophytoene (dehydrosqualene), with 4,4'-diapophytofluene, 4,4'-diapo-zeta-carotene and 4,4'-diapolycopene as intermediates, and 4,4'-diapolycopene as the end product.
4,4\'-diapophytofluene desaturase activity