Converts phytoene into all-trans-neurosporene as the major product, via the intermediary of phytofluene and zeta-carotene, by the introduction of three double bonds. Both intermediates, phytofluene and zeta-carotene, can be used as substrates and converted to neurosporene. 1,2-epoxy phytoene is also a suitable substrate whereas the C30 diapophytoene is not. 15-cis-phytoene + 3 A = 3 AH2 + all-trans-neurosporene Is inhibited by diphenylamine (DPA). Is also slightly inhibited by NAD, NADP or ATP in the presence of FAD. Carotenoid biosynthesis. Belongs to the carotenoid/retinoid oxidoreductase family.