Phytoene synthase

{{Short description|Class of enzymes}}

{{Infobox enzyme

| Name = 15-cis-phytoene synthase

| EC_number = 2.5.1.32

| CAS_number = 50936-61-3

| GO_code =

| image =

| width =

| caption =

}}

Phytoene synthase ({{EC number|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.[http://www.brenda-enzymes.org/php/result_flat.php4?ecno=2.5.1.32 Phytoene synthase]{{cite journal | vauthors = Gregonis DE, Rilling HC | title = The stereochemistry of trans-phytoene synthesis. Some observations on lycopersene as a carotene precursor and a mechanism for the synthesis of cis- and trans-phytoene | journal = Biochemistry | volume = 13 | issue = 7 | pages = 1538–42 | date = March 1974 | pmid = 4819767 | doi = 10.1021/bi00704a033 }}{{cite journal |last1=Chamovitz |first1=Daniel |last2=Misawa |first2=Norihiko |last3=Sandmann |first3=Gerhard |last4=Hirschberg |first4=Joseph |title=Molecular cloning and expression in of a cyanobacterial gene coding for phytoene synthase, a carotenoid biosynthesis enzyme |journal=FEBS Letters |date=27 January 1992 |volume=296 |issue=3 |pages=305–310 |doi=10.1016/0014-5793(92)80310-d}}{{cite journal | vauthors = Misawa N, Truesdale MR, Sandmann G, Fraser PD, Bird C, Schuch W, Bramley PM | title = Expression of a tomato cDNA coding for phytoene synthase in Escherichia coli, phytoene formation in vivo and in vitro, and functional analysis of the various truncated gene products | journal = Journal of Biochemistry | volume = 116 | issue = 5 | pages = 980–5 | date = November 1994 | pmid = 7896759 }} This enzyme catalyses the following chemical reaction

: 2 geranylgeranyl diphosphate $\backslash rightleftharpoons$ 15-cis-phytoene + 2 diphosphate (overall reaction)

:(1a) 2 geranylgeranyl diphosphate $\backslash rightleftharpoons$ diphosphate + prephytoene diphosphate

:(1b) prephytoene diphosphate $\backslash rightleftharpoons$ 15-cis-phytoene + diphosphate

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