Flavonol synthase from Citrus unshiu is a bifunctional dioxygenase |
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Authors: | Lukacin Richard Wellmann Frank Britsch Lothar Martens Stefan Matern Ulrich |
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Institution: | Institut für Pharmazeutische Biologie, Philipps-Universit?t Marburg, Deutschhausstrasse 17 A, D-35037 Marburg, Germany. |
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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. |
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Keywords: | Citrus unshiu Rutaceae Flavonoid biosynthesis Flavonol synthase Dihydroflavonol hydroxylase Bifunctional dioxygenase |
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