:Protostadienol synthase

{{Short description|Class of enzymes}}

{{Infobox enzyme

| Name = Protostadienol synthase

| EC_number = 5.4.99.32

| CAS_number =

| GO_code =

| image =

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Protostadienol synthase ({{EnzExplorer|5.4.99.32}}, PdsA, (S)-2,3-epoxysqualene mutase [cyclizing, (17Z)-protosta-17(20),24-dien-3beta-ol-forming]) is an enzyme with systematic name (3S)-2,3-epoxy-2,3-dihydrosqualene mutase (cyclizing, (17Z)-protosta-17(20),24-dien-3beta-ol-forming).{{cite journal | vauthors = Lodeiro S, Xiong Q, Wilson WK, Ivanova Y, Smith ML, May GS, Matsuda SP | title = Protostadienol biosynthesis and metabolism in the pathogenic fungus Aspergillus fumigatus | journal = Organic Letters | volume = 11 | issue = 6 | pages = 1241–4 | date = March 2009 | pmid = 19216560 | doi = 10.1021/ol802696a }} This enzyme catalyses the following chemical reaction

: (3S)-2,3-epoxy-2,3-dihydrosqualene $\backslash rightleftharpoons$ (17Z)-protosta-17(20),24-dien-3beta-ol

(17Z)-Protosta-17(20),24-dien-3beta-ol is a precursor of the steroidal antibiotic helvolic acid.