All trans phytoene synthase

All-trans-phytoene synthase (EC 2.5.1.99, prephytoene-diphosphate synthase, phytoene synthetase, PSase, geranylgeranyl-diphosphate geranylgeranyltransferase, 15-trans-phytoene synthase) is an enzyme with systematic name geranylgeranyl-diphosphate:geranylgeranyl-diphosphate geranylgeranyltransferase (all-trans-phytoene forming). This enzyme catalyses the following chemical reaction

2 geranylgeranyl diphosphate ⇌ all-trans-phytoene + 2 diphosphate (overall reaction)(1a) 2 geranylgeranyl diphosphate ⇌ diphosphate + prephytoene diphosphate(1b) prephytoene diphosphate ⇌ all-trans-phytoene + diphosphate

This enzyme requires Mn²⁺ for activity.