Phytoene synthase

Phytoene synthase (EC 2.5.1.32, prephytoene-diphosphate synthase, 15-cis-phytoene synthase, PSase, geranylgeranyl-diphosphate geranylgeranyltransferase) is a transferase enzyme involved in the biosynthesis of carotenoids. It catalyzes the conversion of geranylgeranyl pyrophosphate to phytoene. This enzyme catalyses the following chemical reaction

2 geranylgeranyl diphosphate ⇌ 15-cis-phytoene + 2 diphosphate (overall reaction)(1a) 2 geranylgeranyl diphosphate ⇌ diphosphate + prephytoene diphosphate(1b) prephytoene diphosphate ⇌ 15-cis-phytoene + diphosphate

This enzyme requires Mn²⁺ for activity. It belongs to squalene/phytoene synthase family of proteins.