Reaction: a (2R,3S,4S)-leucoanthocyanidin + 2-oxoglutarate + O2 = an anthocyanidin + succinate + CO2 + 2 H2O (overall reaction)
(1a) a (2R,3S,4S)-leucoanthocyanidin + 2-oxoglutarate + O2 = a (4S)- 2,3-dehydroflavan-3,4-diol + succinate + CO2 + H2O
(1b) a (4S)- 2,3-dehydroflavan-3,4-diol = an anthocyanidin + H2O
For diagram of reaction click here.
Glossary: taxifolin = 3,4-dihydroquercitin
Other name(s): leucocyanidin oxygenase; leucocyanidin,2-oxoglutarate:oxygen oxidoreductase; ANS (gene name)
Systematic name: (2R,3S,4S)-leucoanthocyanidin,2-oxoglutarate:oxygen oxidoreductase
Comments: The enzyme requires Fe(II) and ascorbate. It is involved in the pathway by which many flowering plants make anthocyanin flower pigments (glycosylated anthocyandins). The enzyme hydroxylates the C-3 carbon, followed by a trans diaxial elimination, forming a C-2,C-3 enol. The product loses a second water molecule to form anthocyanidins. When assayed in vitro, non-enzymic epimerization of the product can lead to formation of dihydroflavanols. Thus when the substrate is leucocyanidin, a mixture of (+)-taxifolin and (+)-epitaxifolin are formed. The enzyme can also oxidize the formed (+)-taxifolin to quercetin (cf. EC 184.108.40.206, flavonol synthase) [2,3].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
1. Saito, K., Kobayashi, M., Gong, Z., Tanaka, Y. and Yamazaki, M. Direct evidence for anthocyanidin synthase as a 2-oxoglutarate-dependent oxygenase: molecular cloning and functional expression of cDNA from a red forma of Perilla frutescens. Plant J. 17 (1999) 181-190. [PMID: 10074715]
2. Turnbull, J.J., Sobey, W.J., Aplin, R.T., Hassan, A., Firmin, J.L., Schofield, C.J. and Prescott, A.G. Are anthocyanidins the immediate products of anthocyanidin synthase? Chem. Commun. (2000) 2473-2474.
3. Wilmouth, R.C., Turnbull, J.J., Welford, R.W., Clifton, I.J., Prescott, A.G. and Schofield, C.J. Structure and mechanism of anthocyanidin synthase from Arabidopsis thaliana. Structure 10 (2002) 93-103. [PMID: 11796114]
4. Turnbull, J.J., Nagle, M.J., Seibel, J.F., Welford, R.W., Grant, G.H. and Schofield, C.J. The C-4 stereochemistry of leucocyanidin substrates for anthocyanidin synthase affects product selectivity. Bioorg. Med. Chem. Lett. 13 (2003) 3853-3857. [PMID: 14552794]
5. Wellmann, F., Griesser, M., Schwab, W., Martens, S., Eisenreich, W., Matern, U. and Lukacin, R. Anthocyanidin synthase from Gerbera hybrida catalyzes the conversion of (+)-catechin to cyanidin and a novel procyanidin. FEBS Lett. 580 (2006) 1642-1648. [PMID: 16494872]