Biosynthesis of cyclic carotenoids: Biochemistry and molecular genetics of the reaction sequence

Cyclic carotenids are found in the photosynthetic apparatus of higher plants. The biosynthesis of these pigments has been under investigation for two decades. Especially with in vitro systems from chromoplasts and unicellular cynaobacteria. new information has been obtained on the enzymatic reactions in carotenogenesis. Very recently, progress in the identification and cloning of several genes from the carotenogenic pathway has been made with bacteria, cyanobacteria and fungi. The new developments in biochemistry and molecular biology of cyclic carotenoids are reviewed, and the consequences of the results obtained by molecular genetics on the general understanding of the biosynthetic pathway of carotenoids are discussed, especially the desaturation and isomerization reactions.