Phytoene desaturase (lycopene-forming) Phytoene desaturase (lycopene-forming) Phytoene desaturase (lycopene-forming) (CrtI, "four-step phytoene desaturase") (, "15-cis-phytoene:acceptor oxidoreductase (lycopene-forming)") are enzymes found in archaea, bacteria and fungi that are involved in carotenoid biosynthesis. They catalyze the conversion of colorless 15-"cis"-phytoene into a bright red lycopene in a biochemical pathway called the poly-trans pathway. The same process in plants and cyanobacteria utilizes four separate enzymes in a poly-cis pathway. Bacterial phytoene desaturases were shown to require FAD as a cofactor for their function. During the chemical reaction in total four additional double bonds are introduced into phytoene: In 2000 it was discovered that the gene insertion
Lycopene Lycopene is a key intermediate in the biosynthesis of carotenoids, such as beta-carotene, and xanthophylls. The unconditioned biosynthesis of lycopene in eukaryotic plants and in prokaryotic cyanobacteria is similar, as are the enzymes involved. Synthesis begins with mevalonic acid, which is converted into dimethylallyl pyrophosphate. This is then condensed with three molecules of isopentenyl pyrophosphate (an isomer of dimethylallyl pyrophosphate), to give the 20-carbon geranylgeranyl pyrophosphate. Two molecules of this product are then condensed in a tail-to-tail configuration to give the 40-carbon phytoene, the first committed step in carotenoid biosynthesis. Through several desaturation steps, phytoene is converted into lycopene. The