The Enzyme Database

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EC 1.3.1.51     
Accepted name: 2′-hydroxydaidzein reductase
Reaction: 2′-hydroxy-2,3-dihydrodaidzein + NADP+ = 2′-hydroxydaidzein + NADPH + H+
For diagram of glyceollin biosynthesis (part 1), click here
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.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 126125-01-7
References:
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. [DOI] [PMID: 2306102]
[EC 1.3.1.51 created 1992, modified 2004]
 
 
EC 1.14.13.86      
Deleted entry: 2-hydroxyisoflavanone synthase. This enzyme was classified on the basis of an incorrect reaction. The activity is covered by EC 1.14.14.87, 2-hydroxyisoflavanone synthase
[EC 1.14.13.86 created 2004, deleted 2013]
 
 
EC 1.14.13.89      
Transferred entry: isoflavone 2-hydroxylase. Now EC 1.14.14.90, isoflavone 2-hydroxylase
[EC 1.14.13.89 created 2005, deleted 2018]
 
 
EC 1.14.13.136      
Transferred entry: 2-hydroxyisoflavanone synthase. Now EC 1.14.14.87, 2-hydroxyisoflavanone synthase
[EC 1.14.13.136 created 2011, modified 2013, deleted 2018]
 
 
EC 1.14.14.87     
Accepted name: 2-hydroxyisoflavanone synthase
Reaction: (1) liquiritigenin + O2 + [reduced NADPH—hemoprotein reductase] = 2,4′,7-trihydroxyisoflavanone + H2O + [oxidized NADPH—hemoprotein reductase]
(2) (2S)-naringenin + O2 + [reduced NADPH—hemoprotein reductase] = 2,4′,5,7-tetrahydroxyisoflavanone + H2O + [oxidized NADPH—hemoprotein reductase]
For diagram of daidzein biosynthesis, click here
Glossary: liquiritigenin = 4′,7-dihydroxyflavanone
(2S)-naringenin = 4′,5,7-dihydroxyflavanone
2,4′,5,7-tetrahydroxyisoflavanone = 2-hydroxy-2,3-dihydrogenistein
Other name(s): CYP93C; IFS; isoflavonoid synthase
Systematic name: liquiritigenin, [reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (hydroxylating, aryl migration)
Comments: A cytochrome P-450 (heme thiolate) protein found in plants. The reaction involves the migration of the 2-phenyl group of the flavanone to the 3-position of the isoflavanone. The 2-hydroxyl group is derived from the oxygen molecule. EC 4.2.1.105, 2-hydroxyisoflavanone dehydratase, acts on the products with loss of water and formation of genistein and daidzein, respectively.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Kochs, G. and Grisebach, H. Enzymic synthesis of isoflavones. Eur. J. Biochem. 155 (1986) 311–318. [DOI] [PMID: 3956488]
2.  Hashim, M.F., Hakamatsuka, T., Ebizuka, Y. and Sankawa, U. Reaction mechanism of oxidative rearrangement of flavanone in isoflavone biosynthesis. FEBS Lett. 271 (1990) 219–222. [DOI] [PMID: 2226805]
3.  Steele, C. L., Gijzen, M., Qutob, D. and Dixon, R.A. Molecular characterization of the enzyme catalyzing the aryl migration reaction of isoflavonoid biosynthesis in soybean. Arch. Biochem. Biophys. 367 (1999) 146–150. [DOI] [PMID: 10375412]
4.  Sawada, Y., Kinoshita, K., Akashi, T., Aoki, T. and Ayabe, S. Key amino acid residues required for aryl migration catalysed by the cytochrome P450 2-hydroxyisoflavanone synthase. Plant J. 31 (2002) 555–564. [DOI] [PMID: 12207646]
5.  Sawada, Y. and Ayabe, S. Multiple mutagenesis of P450 isoflavonoid synthase reveals a key active-site residue. Biochem. Biophys. Res. Commun. 330 (2005) 907–913. [DOI] [PMID: 15809082]
[EC 1.14.14.87 created 2011 as EC 1.14.13.136, modified 2013, transferred 2018 to EC 1.14.14.87]
 
 
EC 1.14.14.90     
Accepted name: isoflavone 2′-hydroxylase
Reaction: an isoflavone + [reduced NADPH—hemoprotein reductase] + O2 = a 2′-hydroxyisoflavone + [oxidized NADPH—hemoprotein reductase] + H2O
For diagram of the biosynthesis of formononetin and derivatives, click here
Other name(s): isoflavone 2′-monooxygenase; CYP81E1; CYP Ge-3
Systematic name: isoflavone,[reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (2′-hydroxylating)
Comments: A cytochrome P-450 (heme-thiolate) protein. Acts on daidzein, formononetin and genistein. EC 1.14.14.89, 4′-methoxyisoflavone 2′-hydroxylase, has the same reaction but is more specific as it requires a 4′-methoxyisoflavone.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 110183-49-8
References:
1.  Akashi, T., Aoki, T. and Ayabe, S.-I. CYP81E1, a cytochrome P450 cDNA of licorice (Glycyrrhiza echinata L.), encodes isoflavone 2′-hydroxylase. Biochem. Biophys. Res. Commun. 251 (1998) 67–70. [DOI] [PMID: 9790908]
[EC 1.14.14.90 created 2005 as EC 1.14.13.89, transferred 2018 to EC 1.14.14.90]
 
 
EC 2.1.1.46     
Accepted name: isoflavone 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + a 4′-hydroxyisoflavone = S-adenosyl-L-homocysteine + a 4′-methoxyisoflavone
For diagram of the biosynthesis of biochanin A, click here and for diagram of the biosynthesis of formononetin and derivatives, click here
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.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 55071-80-2
References:
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. [DOI] [PMID: 4452353]
[EC 2.1.1.46 created 1976, modified 2011]
 
 
EC 2.1.1.150     
Accepted name: isoflavone 7-O-methyltransferase
Reaction: S-adenosyl-L-methionine + a 7-hydroxyisoflavone = S-adenosyl-L-homocysteine + a 7-methoxyisoflavone
For diagram of the biosynthesis of formononetin and derivatives, click here and of biochanin A, click here
Systematic name: S-adenosyl-L-methionine:hydroxyisoflavone 7-O-methyltransferase
Comments: The enzyme from alfalfa can methylate daidzein, genistein and 6,7,4′-trihydroxyisoflavone but not flavones or flavanones.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 136111-54-1
References:
1.  Edwards, R. and Dixon, R.A. Isoflavone O-methyltransferase activities in elicitor-treated cell suspension cultures of Medicago sativa. Phytochemistry 30 (1991) 2597–2606.
2.  He, X.Z. and Dixon, R.A. Genetic manipulation of isoflavone 7-O-methyltransferase enhances biosynthesis of 4′-O-methylated isoflavonoid phytoalexins and disease resistance in alfalfa. Plant Cell 12 (2000) 1689–1702. [PMID: 11006341]
3.  He, X.-Z. and Dixon, R.A. Affinity chromatography, substrate/product specificity, and amino acid sequence analysis of an isoflavone O-methyltransferase from alfalfa (Medicago sativa L.). Arch. Biochem. Biophys. 336 (1996) 121–129. [DOI] [PMID: 8951042]
4.  He, X.Z., Reddy, J.T. and Dixon, R.A. Stress responses in alfalfa (Medicago sativa L). XXII. cDNA cloning and characterization of an elicitor-inducible isoflavone 7-O-methyltransferase. Plant Mol. Biol. 36 (1998) 43–54. [PMID: 9484461]
5.  Liu, C.-J. and Dixon, R.A. Elicitor-induced association of isoflavone O-methyltransferase with endomembranes prevents the formation and 7-O-methylation of daidzein during isoflavonoid phytoalexin biosynthesis. Plant Cell 13 (2001) 2643–2658. [DOI] [PMID: 11752378]
6.  Zubieta, C., He, X.-Z., Dixon, R.A. and Noel, J.P. Structures of two natural product methyltransferases reveal the basis for substrate specificity in plant O-methyltransferases. Nat. Struct. Biol. 8 (2001) 271–279. [DOI] [PMID: 11224575]
[EC 2.1.1.150 created 2003]
 
 
EC 2.1.1.154     
Accepted name: isoliquiritigenin 2′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + isoliquiritigenin = S-adenosyl-L-homocysteine + 2′-O-methylisoliquiritigenin
For diagram of daidzein biosynthesis, click here
Glossary: isoliquiritigenin = 4,2′,4′-trihydroxychalcone
Other name(s): chalcone OMT; CHMT
Systematic name: S-adenosyl-L-methionine:isoliquiritigenin 2′-O-methyltransferase
Comments: Not identical to EC 2.1.1.65, licodione 2′-O-methyltransferase [2]. While EC 2.1.1.154, isoliquiritigenin 2′-O-methyltransferase can use licodione as a substrate, EC 2.1.1.65 cannot use isoliquiritigenin as a substrate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 139317-14-9
References:
1.  Maxwell, C.A., Edwards, R. and Dixon, R.A. Identification, purification, and characterization of S-adenosyl-L-methionine: isoliquiritigenin 2′-O-methyltransferase from alfalfa (Medicago sativa L.). Arch. Biochem. Biophys. 293 (1992) 158–166. [DOI] [PMID: 1731632]
2.  Ichimura, M., Furuno, T., Takahashi, T., Dixon, R.A. and Ayabe, S. Enzymic O-methylation of isoliquiritigenin and licodione in alfalfa and licorice cultures. Phytochemistry 44 (1997) 991–995. [DOI] [PMID: 9055445]
[EC 2.1.1.154 created 2004]
 
 
EC 2.1.1.212     
Accepted name: 2,7,4′-trihydroxyisoflavanone 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + 2,4′,7-trihydroxyisoflavanone = S-adenosyl-L-homocysteine + 2,7-dihydroxy-4′-methoxyisoflavanone
For diagram of daidzein biosynthesis, click here
Other name(s): SAM:2,7,4′-trihydroxyisoflavanone 4′-O-methyltransferase; HI4′OMT; HMM1; MtIOMT5; S-adenosyl-L-methionine:2,7,4′-trihydroxyisoflavanone 4′-O-methyltransferase
Systematic name: S-adenosyl-L-methionine:2,4′,7-trihydroxyisoflavanone 4′-O-methyltransferase
Comments: Specifically methylates 2,4′,7-trihydroxyisoflavanone on the 4′-position. No activity with isoflavones [2]. The enzyme is involved in formononetin biosynthesis in legumes [1]. The protein from pea (Pisum sativum) also methylates (+)-6a-hydroxymaackiain at the 3-position (cf. EC 2.1.1.270, (+)-6a-hydroxymaackiain 3-O-methyltransferase) [4].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Akashi, T., Sawada, Y., Shimada, N., Sakurai, N., Aoki, T. and Ayabe, S. cDNA cloning and biochemical characterization of S-adenosyl-L-methionine: 2,7,4′-trihydroxyisoflavanone 4′-O-methyltransferase, a critical enzyme of the legume isoflavonoid phytoalexin pathway. Plant Cell Physiol. 44 (2003) 103–112. [PMID: 12610212]
2.  Deavours, B.E., Liu, C.J., Naoumkina, M.A., Tang, Y., Farag, M.A., Sumner, L.W., Noel, J.P. and Dixon, R.A. Functional analysis of members of the isoflavone and isoflavanone O-methyltransferase enzyme families from the model legume Medicago truncatula. Plant Mol. Biol. 62 (2006) 715–733. [DOI] [PMID: 17001495]
3.  Liu, C.J., Deavours, B.E., Richard, S.B., Ferrer, J.L., Blount, J.W., Huhman, D., Dixon, R.A. and Noel, J.P. Structural basis for dual functionality of isoflavonoid O-methyltransferases in the evolution of plant defense responses. Plant Cell 18 (2006) 3656–3669. [DOI] [PMID: 17172354]
4.  Akashi, T., VanEtten, H.D., Sawada, Y., Wasmann, C.C., Uchiyama, H. and Ayabe, S. Catalytic specificity of pea O-methyltransferases suggests gene duplication for (+)-pisatin biosynthesis. Phytochemistry 67 (2006) 2525–2530. [DOI] [PMID: 17067644]
[EC 2.1.1.212 created 2011]
 
 
EC 2.1.1.231     
Accepted name: flavonoid 4′-O-methyltransferase
Reaction: S-adenosyl-L-methionine + a 4′-hydroxyflavanone = S-adenosyl-L-homocysteine + a 4′-methoxyflavanone
For diagram of naringenin methyl ethers biosynthesis, click here
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.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
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. [DOI] [PMID: 15961179]
[EC 2.1.1.231 created 2011]
 
 
EC 2.3.1.170     
Accepted name: 6′-deoxychalcone synthase
Reaction: 3 malonyl-CoA + 4-coumaroyl-CoA + NADPH + H+ = 4 CoA + isoliquiritigenin + 3 CO2 + NADP+ + H2O
For diagram of daidzein biosynthesis, click here
Glossary: isoliquiritigenin = 4,2′,4′-trihydroxychalcone
liquiritigenin = 7,4′-dihydroxyflavanone
Systematic name: malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclizing, reducing)
Comments: Isoliquiritigenin is the precursor of liquiritigenin, a 5-deoxyflavanone.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 114308-23-5
References:
1.  Ayabe, S., Udagawa, A. and Furuya, T. NAD(P)H-dependent 6′-deoxychalcone synthase activity in Glycyrrhiza echinata cells induced by yeast extract. Arch. Biochem. Biophys. 261 (1988) 458–462. [DOI] [PMID: 3355160]
[EC 2.3.1.170 created 2004]
 
 
EC 2.4.1.170     
Accepted name: isoflavone 7-O-glucosyltransferase
Reaction: UDP-glucose + an isoflavone = UDP + an isoflavone 7-O-β-D-glucoside
For diagram of the biosynthesis of biochanin A, click here and for diagram of the biosynthesis of formononetin and derivatives, click here
Other name(s): uridine diphosphoglucose-isoflavone 7-O-glucosyltransferase; UDPglucose-favonoid 7-O-glucosyltransferase; UDPglucose:isoflavone 7-O-glucosyltransferase
Systematic name: UDP-glucose:isoflavone 7-O-β-D-glucosyltransferase
Comments: The 4′-methoxy isoflavones biochanin A and formononetin and, more slowly, the 4′-hydroxyisoflavones genistein and daidzein, can act as acceptors. The enzyme does not act on isoflavanones, flavones, flavanones, flavanols or coumarins.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 97089-62-8
References:
1.  Köster, J. and Barz, W. UDP-glucose:isoflavone 7-O-glucosyltransferase from roots of chick pea (Cicer arietinum L.). Arch. Biochem. Biophys. 212 (1981) 98–104. [DOI] [PMID: 6458246]
[EC 2.4.1.170 created 1989]
 
 
EC 4.2.1.105     
Accepted name: 2-hydroxyisoflavanone dehydratase
Reaction: (1) 2,4′,7-trihydroxyisoflavanone = daidzein + H2O
(2) 2,4′,5,7-tetrahydroxyisoflavanone = genistein + H2O
For diagram of biochanin A biosynthesis, click here and for diagram of daidzein biosynthesis, click here
Glossary: daidzein = 4′,7-dihydroxyisoflavone
genistein = 4′,5,7-dihydroxyisoflavone
Other name(s): 2,7,4′-trihydroxyisoflavanone hydro-lyase; 2,7,4′-trihydroxyisoflavanone hydro-lyase (daidzein-forming)
Systematic name: 2,4′,7-trihydroxyisoflavanone hydro-lyase (daidzein-forming)
Comments: Catalyses the final step in the formation of the isoflavonoid skeleton. The reaction also occurs spontaneously.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 166800-10-8
References:
1.  Hakamatsuka, T., Mori, K., Ishida, S., Ebizuka, Y and Sankawa, U. Purification of 2-hydroxyisoflavanone dehydratase from the cell cultures of Pueraria lobata. Phytochemistry 49 (1998) 497–505.
[EC 4.2.1.105 created 2004, modified 2013]
 
 
EC 5.5.1.6     
Accepted name: chalcone isomerase
Reaction: a chalcone = a flavanone
For diagram of daidzein biosynthesis, click here and for diagram of flavonoid biosynthesis, click here
Other name(s): chalcone-flavanone isomerase; flavanone lyase (decyclizing)
Systematic name: flavanone lyase (ring-opening)
Links to other databases: BRENDA, EXPASY, GTD, KEGG, MetaCyc, PDB, CAS registry number: 9073-57-8
References:
1.  Moustafa, E. and Wong, E. Purification and properties of chalcone-flavanone isomerase from soya bean seed. Phytochemistry 6 (1967) 625–632.
[EC 5.5.1.6 created 1972]
 
 


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