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
Carotenosis Carotenosis An excess of dietary carotenoids may cause a marked orange discoloration of the outermost skin layer. This benign and reversible condition – which is most easily observed in light-skinned people and may be mistaken for jaundice – is known as carotenosis or carotenoderma or carotenodermia. Carotenemia, or carotenaemia (xanthaemia), is the presence of the orange pigment carotene in the blood from excessive intake of carrots or other vegetables containing the pigment resulting in increased serum carotenoids. Carotenoids are lipid-soluble compounds that include alpha- and beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin. The primary serum carotenoids are beta-carotene, lycopene, and lutein.