The enzyme, isolated from the archaeon Haloarcula japonica, is involved in the biosynthesis of the C50 carotenoid bacterioruberin. In this pathway it catalyses the desaturation of the C-3,4 double bond in dihydroisopentenyldehydrorhodopin and the desaturation of the C-3′-4′ double bond in dihydrobisanhydrobacterioruberin.