Phytoene desaturase (lycopene-forming) (CrtI, four-step phytoene desaturase) (
EC1.3.99.31, 15-cis-phytoene:acceptor oxidoreductase (lycopene-forming)) are
enzymes found in
archaea,
bacteria and
fungi that are involved in
carotenoid biosynthesis.[2] 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.[3]
Biochemistry
The conversion of phytoene to lycopene in plants and cyanobacteria (left) compared to bacteria and fungi(right).
Bacterial phytoene desaturases were shown to require FAD as a cofactor for their function.[4] During the
chemical reaction in total four additional
double bonds are introduced into phytoene:
In 2000 it was discovered that the
gene insertion of a bacterial phytoene desaturase into
transgenic tomatoes increased the lycopene content without the need to alter several of the plants enzymes.[5] This approach was later used in
rice to increase its
β-carotene content resulting in the
Golden Rice project.