Journal
PHYTOCHEMISTRY
Volume 62, Issue 3, Pages 287-292Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0031-9422(02)00567-8
Keywords
Citrus unshiu; Rutaceae; flavonoid biosynthesis; flavonol synthase; dihydroflavonol hydroxylase; bifunctional dioxygenase
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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 H-1 NMR and CD spectroscopies as (-)-trans-dihydrokaempferol. The data demonstrate that Citrus flavonol synthase encompasses an additional nonspecific activity trans-hydroxylating the flavanones (2S)-naringenin as well as the unnatural (2R)-naringenin at C-3. (C) 2003 Elsevier Science Ltd. All rights reserved.
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