Flavonol synthase from Citrus unshiu is a bifunctional dioxygenase

Phytochemistry. 2003 Feb;62(3):287-92. doi: 10.1016/s0031-9422(02)00567-8.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatography, Thin Layer
  • Circular Dichroism
  • Citrus / enzymology*
  • Escherichia coli / metabolism
  • Flavanones*
  • Flavonoids / biosynthesis
  • Flavonoids / chemistry
  • Flavonoids / metabolism
  • Kaempferols*
  • Mixed Function Oxygenases / metabolism*
  • Oxidoreductases / metabolism*
  • Oxygenases / metabolism*
  • Plant Proteins*
  • Quercetin / analogs & derivatives*
  • Quercetin / biosynthesis
  • Stereoisomerism


  • Flavanones
  • Flavonoids
  • Kaempferols
  • Plant Proteins
  • kaempferol
  • aromadedrin
  • Quercetin
  • Mixed Function Oxygenases
  • Oxidoreductases
  • Oxygenases
  • flavonol synthase
  • naringenin