In vitro carotenogenesis and characterization of the phytoene desaturase reaction in Anacystis.

An in vitro system for carotenogenesis has been developed from the cyanobacterium Anacystis. Precursor conversion is highly effective and almost no colored intermediates before beta-carotene accumulate. These cell-free reactions have been employed to characterize the phytoene desaturation reaction. Phytoene desaturation is dependent on NAD(P)+ and oxygen but insensitive to inhibitors of plant-type monooxygenases. This result suggests a hydride/proton transfer as mechanism for insertion of a double bond into phytoene. Furthermore, feed-back regulation of phytoene desaturase could be demonstrated for most of the subsequent carotenes.