Reaction specificities of the ε-ionone-forming lycopene cyclase from rice (Oryza sativa) elucidated in vitro.
Lycopene cyclases responsible for the formation of ε-ionone rings (LCYe) mark a plant-specific bifurcation of carotenogenesis. We investigated purified rice LCYe (OsLCYe) in a liposome-based biphasic assay system. OsLCYe depends on reduced flavin cofactors stabilizing a transient state formed during the non-redox cyclization reaction. In contrast to OsLCYb, OsLCYe produces predominantly monocyclic products and monocyclic carotene intermediates are not suitable substrates. Determination of the OsLCYe reaction specificities and the combined use of OsLCYb allow the characterization of the reaction sequence leading to heterocyclic carotenoids. It was also found that 5-cis-lycopene, which was thought to be decisive for ε-cyclization, was not involved in the reaction, with OsLCYe acting as an exclusion filter for this naturally occurring isomer.
Faculty of Biology, Centre for Biological Signaling Studies (BIOSS), University of Freiburg, D-79104 Freiburg, Germany.
SourceFEBS letters 586:19 2012 Sep 21 pg 3415-20
Pub Type(s)Journal Article
Research Support, Non-U.S. Gov't