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.
Biochemistry
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:
15-cis-phytoene + 4 acceptor all-trans-lycopene + 4 reduced acceptor (overall reaction) (1a) 15-cis-phytoene + acceptor all-trans-phytofluene + reduced acceptor (1b) all-trans-phytofluene + acceptor all-trans-zeta-carotene + reduced acceptor (1c) all-trans-zeta-carotene + acceptor all-trans-neurosporene + reduced acceptor: (1d) all-trans-neurosporene + acceptor all-trans-lycopene + reduced acceptor
Applications 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. This approach was later used in rice to increase its β-carotene content resulting in the Golden Rice project.
See also 15-Cis-phytoene desaturase Phytoene desaturase (neurosporene-forming) Phytoene desaturase (zeta-carotene-forming) Phytoene desaturase (3,4-didehydrolycopene-forming)
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