Carotenoid isomerooxygenase (EC 1.13.11.65, ninaB (gene)) is an enzyme with systematic name zeaxanthin:oxygen 15,15'-oxidoreductase (bond-cleaving, cis-isomerizing). This enzyme catalyses the following chemical reactionzeaxanthin + O2 (3R)-11-cis-3-hydroxyretinal + (3R)-all-trans-3-hydroxyretinal