title: Flavonol synthase from Citrus unshiu is a bifunctional dioxygenase.
abstract: Flavonol synthase was classified as a 2-oxoglutarate-dependent dioxygenase converting natural (2R,3R)-dihydroflavonols, i.e. dihydrokaempferol, to the corresponding flavonols (kaempferol). Flavonol synthase from Citrus unshiu (Satsuma mandarin), expressed in Escherichia coli and purified to homogeneity, was shown to accept also (2S)-naringenin as a substrate, producing kaempferol in high yield and assigning sequential flavanone 3beta-hydroxylase and flavonol synthase activities to the enzyme. In contrast, dihydrokaempferol was identified as the predominant product from assays performed with the unnatural (2R)-naringenin as substrate. The product which was not converted any further on repeated incubations was identified by 1H NMR and CD spectroscopies as (-)-trans-dihydrokaempferol. The data demonstrate that Citrus flavonol synthase encompasses an additional non-specific activity trans-hydroxylating the flavanones (2S)-naringenin as well as the unnatural (2R)-naringenin at C-3.
authors.affiliation: Institut für Pharmazeutische Biologie, Philipps-Universität Marburg, Deutschhausstrasse 17 A, D-35037 Marburg, Germany.
authors.forename: Richard
authors.initials: R
authors.lastname: Lukacin
authors.forename: Frank
authors.initials: F
authors.lastname: Wellmann
authors.forename: Lothar
authors.initials: L
authors.lastname: Britsch
authors.forename: Stefan
authors.initials: S
authors.lastname: Martens
authors.forename: Ulrich
authors.initials: U
authors.lastname: Matern
mesh_terms: D002855:Chromatography, Thin Layer; D002942:Circular Dichroism; D002957:Citrus / Q000201:enzymology*; D004926:Escherichia coli / Q000378:metabolism; D044950:Flavanones; D005419:Flavonoids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D044949:Kaempferols; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism*; D010940:Plant Proteins; D011794:Quercetin / Q000031:analogs & derivatives* / Q000096:biosynthesis; D013237:Stereoisomerism
chemical_list: D044950:Flavanones; D005419:Flavonoids; D044949:Kaempferols; D010940:Plant Proteins; C006552:kaempferol; C080220:aromadedrin; D011794:Quercetin; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D010105:Oxygenases; C085313:flavonol synthase; C005273:naringenin