| Phytoene desaturase (lycopene-forming) | |
| Ec Number: | 1.3.99.31 |
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.[1] 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.[2]
Bacterial phytoene desaturases were shown to require FAD as a cofactor for their function.[3] During the chemical reaction in total four additional double bonds are introduced into phytoene:
15-cis-phytoene + 4 acceptor
\rightleftharpoons
(1a) 15-cis-phytoene + acceptor
\rightleftharpoons
(1b) all-trans-phytofluene + acceptor
\rightleftharpoons
(1c) all-trans-zeta-carotene + acceptor
\rightleftharpoons
(1d) all-trans-neurosporene + acceptor
\rightleftharpoons
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.[4] This approach was later used in rice to increase its β-carotene content resulting in the Golden Rice project.