Reaction specificities of the ε-ionone-forming lycopene cyclase from rice (Oryza sativa) elucidated in vitro

► Lycopene ε-cyclase (LCYe) utilizes FADred or FMNred to catalyze a non-redox reaction. ► With lycopene, LCYe forms δ-carotene and low levels of ε,β-bicyclic carotenes. ► Monocyclic carotenes containing either ring type are not converted. ► Bicyclic carotenoids form from lycopene by LCYe or in a sequence LCYe → LCYb. ► 5-cis-lycopene, hypothesized to be essential for ε-ring formation, is not involved.