Phytoene desaturase (lycopene-forming)
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Phytoene desaturase (lycopene-forming) (CrtI, four-step phytoene desaturase) (EC 1.3.99.31, 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]
| Phytoene desaturase (lycopene-forming) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
Crystallographic structure of a bacterial phytoene desaturase monomer from Pantoea ananatis.[1] | |||||||||
| Identifiers | |||||||||
| EC no. | 1.3.99.31 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| |||||||||
Biochemistry
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:
- 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.[5] This approach was later used in rice to increase its β-carotene content resulting in the Golden Rice project.
