Accepted name: 2′-hydroxydaidzein reductase
Reaction: 2′-hydroxy-2,3-dihydrodaidzein + NADP+ = 2′-hydroxydaidzein + NADPH + H+
Other name(s): NADPH:2′-hydroxydaidzein oxidoreductase; HDR; 2′-hydroxydihydrodaidzein:NADP+ 2′-oxidoreductase
Systematic name: 2′-hydroxy-2,3-dihydrodaidzein:NADP+ 2′-oxidoreductase
Comments: In the reverse reaction, the 2′-hydroxyisoflavone (2′-hydroxydaidzein) is reduced to an isoflavanone. Also acts on 2′-hydroxyformononetin and to a small extent on 2′-hydroxygenistein. Involved in the biosynthesis of the phytoalexin glyceollin. The isoflavones biochanin A, daidzein and genestein as well as the flavonoids apigenin, kaempferol and quercetin do not act as substrates.
1.  Fischer, D., Ebenau-Jehle, C. and Grisebach, H. Phytoalexin synthesis in soybean: purification and characterization of NADPH:2′-hydroxydaidzein oxidoreductase from elicitor-challenged soybean cell cultures. Arch. Biochem. Biophys. 276 (1990) 390–395. [PMID: 2306102]
[EC created 1992, modified 2004]
Deleted entry: 2-hydroxyisoflavanone synthase. This enzyme was classified on the basis of an incorrect reaction. The activity is covered by EC, 2-hydroxyisoflavanone synthase
[EC created 2004, deleted 2013]
Accepted name: flavonoid 3′-monooxygenase
Reaction: a flavonoid + [reduced NADPH—hemoprotein reductase] + O2 = a 3′-hydroxyflavonoid + [oxidized NADPH—hemoprotein reductase] + H2O
Other name(s): CYP75B1 (gene name); flavonoid 3′-hydroxylase; flavonoid 3-hydroxylase (incorrect); NADPH:flavonoid-3′-hydroxylase (incorrect); flavonoid 3-monooxygenase (incorrect)
Systematic name: flavonoid,[reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (3′-hydroxylating)
Comments: A cytochrome P-450 (heme-thiolate) protein found in plants. Acts on a number of flavonoids, including the flavanone naringenin and the flavone apigenin. Does not act on 4-coumarate or 4-coumaroyl-CoA.
1.  Forkmann, G., Heller, W. and Grisebach, H. Anthocyanin biosynthesis in flowers of Matthiola incana flavanone 3- and flavonoid 3′-hydroxylases. Z. Naturforsch. C: Biosci. 35 (1980) 691–695.
2.  Brugliera, F., Barri-Rewell, G., Holton, T.A. and Mason, J.G. Isolation and characterization of a flavonoid 3′-hydroxylase cDNA clone corresponding to the Ht1 locus of Petunia hybrida. Plant J. 19 (1999) 441–451. [PMID: 10504566]
3.  Schoenbohm, C., Martens, S., Eder, C., Forkmann, G. and Weisshaar, B. Identification of the Arabidopsis thaliana flavonoid 3′-hydroxylase gene and functional expression of the encoded P450 enzyme. Biol. Chem. 381 (2000) 749–753. [PMID: 11030432]
[EC created 1983 as EC, transferred 2018 to EC]
Accepted name: isoflavone 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + a 4′-hydroxyisoflavone = S-adenosyl-L-homocysteine + a 4′-methoxyisoflavone
Other name(s): 4′-hydroxyisoflavone methyltransferase; isoflavone methyltransferase; isoflavone O-methyltransferase
Systematic name: S-adenosyl-L-methionine:4′-hydroxyisoflavone 4′-O-methyltransferase
Comments: Requires Mg2+ for activity. The enzyme catalyses the methylation of daidzein and genistein. It does not methylate naringenin, apigenin, luteolin or kaempferol.
1.  Wengenmayer, H., Ebel, J. and Grisebach, H. Purification and properties of a S-adenosylmethionine: isoflavone 4′-O-methyltransferase from cell suspension cultures of Cicer arietinum L. Eur. J. Biochem. 50 (1974) 135–143. [PMID: 4452353]
[EC created 1976, modified 2011]
Accepted name: apigenin 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + apigenin = S-adenosyl-L-homocysteine + acacetin
Glossary: apigenin = 4′,5,7-trihydroxyflavone
acacetin = 4′-methoxy-5,7-dihydroxyflavone
naringenin = 4′,5,7-trihydroxyflavan-4-one
Other name(s): flavonoid O-methyltransferase; flavonoid methyltransferase; S-adenosyl-L-methionine:5,7,4′-trihydroxyflavone 4′-O-methyltransferase
Systematic name: S-adenosyl-L-methionine:apigenin 4′-O-methyltransferase
Comments: Converts apigenin into acacetin. Naringenin can also act as an acceptor, but more slowly.
1.  Kuroki, G. and Poulton, J.E. The para-O-methylation of apigenin to acacetin by cell-free extracts of Robinia pseudoacacia L. Z. Naturforsch. C: Biosci. 36 (1981) 916–920.
[EC created 1984]
Accepted name: kaempferol 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + kaempferol = S-adenosyl-L-homocysteine + kaempferide
Glossary: kaempferide = 3,5,7-trihydroxy-4′-methoxyflavone
Other name(s): S-adenosyl-L-methionine:flavonoid 4′-O-methyltransferase; F 4′-OMT
Systematic name: S-adenosyl-L-methionine:kaempferol 4′-O-methyltransferase
Comments: The enzyme acts on the hydroxy group in the 4′-position of some flavones, flavanones and isoflavones. Kaempferol, apigenin and kaempferol triglucoside are substrates, as is genistein, which reacts more slowly. Compounds with an hydroxy group in the 3′ and 4′ positions, such as quercetin and eriodictyol, do not act as substrates. Similar to EC, apigenin 4′-O-methyltransferase and EC, 3,7-dimethylquercetin 4′-O-methyltransferase.
1.  Curir, P., Lanzotti, V., Dolci, M., Dolci, P., Pasini, C. and Tollin, G. Purification and properties of a new S-adenosyl-L-methionine:flavonoid 4′-O-methyltransferase from carnation (Dianthus caryophyllus L.). Eur. J. Biochem. 270 (2003) 3422–3431. [PMID: 12899699]
[EC created 2004]
Accepted name: flavonoid 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + a 4′-hydroxyflavanone = S-adenosyl-L-homocysteine + a 4′-methoxyflavanone
Glossary: naringenin = 4′,5,7-trihydroxyflavan-4-one
Other name(s): SOMT-2; 4′-hydroxyisoflavone methyltransferase
Systematic name: S-adenosyl-L-methionine:flavonoid 4′-O-methyltransferase
Comments: The enzyme catalyses the 4′-methylation of naringenin. In vitro it catalyses the 4′-methylation of apigenin, quercetin, daidzein and genistein.
1.  Kim, D.H., Kim, B.G., Lee, Y., Ryu, J.Y., Lim, Y., Hur, H.G. and Ahn, J.H. Regiospecific methylation of naringenin to ponciretin by soybean O-methyltransferase expressed in Escherichia coli. J. Biotechnol. 119 (2005) 155–162. [PMID: 15961179]
[EC created 2011]
Accepted name: isoflavone-7-O-β-glucoside 6′′-O-malonyltransferase
Reaction: malonyl-CoA + biochanin A 7-O-β-D-glucoside = CoA + biochanin A 7-O-(6-O-malonyl-β-D-glucoside)
Other name(s): flavone/flavonol 7-O-β-D-glucoside malonyltransferase; flavone (flavonol) 7-O-glycoside malonyltransferase; malonyl-CoA:flavone/flavonol 7-O-glucoside malonyltransferase; MAT-7; malonyl-coenzyme A:isoflavone 7-O-glucoside-6′′-malonyltransferase; malonyl-coenzyme A:flavone/flavonol-7-O-glycoside malonyltransferase
Systematic name: malonyl-CoA:isoflavone-7-O-β-D-glucoside 6′′-O-malonyltransferase
Comments: The 6-position of the glucose residue of formononetin can also act as acceptor; some other 7-O-glucosides of isoflavones, flavones and flavonols can also act, but more slowly.
1.  Koester, J., Bussmann, R. and Barz, W. Malonyl-coenzyme A:isoflavone 7-O-glucoside-6′′-O-malonyltransferase from roots of chick pea (Cicer arietinum L.). Arch. Biochem. Biophys. 234 (1984) 513–521. [PMID: 6497385]
2.  Matern, U., Feser, C. and Hammer, D. Further characterization and regulation of malonyl-coenzyme A: flavonoid glucoside malonyltransferases from parsley cell suspension cultures. Arch. Biochem. Biophys. 226 (1983) 206–217. [PMID: 6639051]
[EC created 1989]
Accepted name: flavone 7-O-β-glucosyltransferase
Reaction: UDP-glucose + 5,7,3′,4′-tetrahydroxyflavone = UDP + 7-O-β-D-glucosyl-5,7,3′,4′-tetrahydroxyflavone
Other name(s): UDP-glucose-apigenin β-glucosyltransferase; UDP-glucose-luteolin β-D-glucosyltransferase; uridine diphosphoglucose-luteolin glucosyltransferase; uridine diphosphoglucose-apigenin 7-O-glucosyltransferase; UDP-glucosyltransferase (ambiguous)
Systematic name: UDP-glucose:5,7,3′,4′-tetrahydroxyflavone 7-O-β-D-glucosyltransferase
Comments: A number of flavones, flavanones and flavonols can function as acceptors. Different from EC (flavonol 3-O-glucosyltransferase).
1.  Sutter, A., Ortmann, R. and Grisebach, H. Purification and properties of an enzyme from cell suspension cultures of parsley catalyzing the transfer of D-glucose from UDP-D-glucose to flavonoids. Biochim. Biophys. Acta 258 (1972) 71–87. [PMID: 5058406]
[EC created 1976]
Accepted name: flavanone 7-O-glucoside 2′′-O-β-L-rhamnosyltransferase
Reaction: UDP-β-L-rhamnose + a flavanone 7-O-β-D-glucoside = UDP + a flavanone 7-O-[α-L-rhamnosyl-(1→2)-β-D-glucoside]
Glossary: UDP-β-L-rhamnose = UDP-6-deoxy-β-L-mannose
Other name(s): UDP-rhamnose:flavanone-7-O-glucoside-2′′-O-rhamnosyltransferase; 1→2 UDP-rhamnosyltransferase; UDP-L-rhamnose:flavanone-7-O-glucoside 2′′-O-β-L-rhamnosyltransferase
Systematic name: UDP-β-L-rhamnose:flavanone-7-O-glucoside 2′′-O-α-L-rhamnosyltransferase
Comments: Acts on the 7-O-glucoside of naringenin and hesperetin, also the flavone 7-O-glucosides of luteolin and apigenin.
1.  Bar-Peled, M., Lewinsohn, E., Fluhr, R. and Gressel, J. UDP-rhamnose:flavanone-7-O-glucoside-2′′-O-rhamnosyltransferase. Purification and characterization of an enzyme catalyzing the production of bitter compounds in citrus. J. Biol. Chem. 266 (1991) 20953–20959. [PMID: 1939145]
[EC created 2004]
Accepted name: flavone apiosyltransferase
Reaction: UDP-α-D-apiose + apigenin 7-O-β-D-glucoside = UDP + apigenin 7-O-[β-D-apiosyl-(1→2)-β-D-glucoside]
Glossary: apigenin = 4′,5,7-trihydroxyflavone
β-D-apiose = (2R,3R,4R)-4-(hydroxymethyl)tetrahydrofuran-2,3,4-triol
Other name(s): uridine diphosphoapiose-flavone apiosyltransferase; UDP-apiose:7-O-(β-D-glucosyl)-flavone apiosyltransferase
Systematic name: UDP-apiose:5,4′-dihydroxyflavone 7-O-β-D-glucoside 2′′-O-β-D-apiofuranosyltransferase
Comments: 7-O-β-D-Glucosides of a number of flavonoids and of 4-substituted phenols can act as acceptors.
1.  Ortmann, R., Sutter, A. and Grisebach, H. Purification and properties of UDPapiose: 7-O-(β-D-glucosyl)-flavone apiosyltransferase from cell suspension cultures of parsley. Biochim. Biophys. Acta 289 (1972) 293–302. [PMID: 4650134]
[EC created 1976]

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