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1.1.1.246

Transferred entry:

pterocarpin synthase. This activity is now known to be catalysed by two enzymes, vestitone reductase (EC 1.1.1.348) and medicarpin synthase (EC 4.2.1.139).

[EC 1.1.1.246 created 1992, deleted 2013]

1.1.1.348

Accepted name:

(3R)-2′-hydroxyisoflavanone reductase

Reaction:

a (4R)-4,2′-dihydroxyisoflavan + NADP⁺ = a (3R)-2′-hydroxyisoflavanone + NADPH + H⁺

For diagram of medicarpin and formononetin derivatives biosynthesis, click here

Glossary:

(3R)-vestitone = (3R)-2′,7-dihydroxy-4′-methoxyisoflavanone

Other name(s):

vestitone reductase; pterocarpin synthase (incorrect); pterocarpan synthase (incorrect)

Systematic name:

(3R)-2′-hydroxyisoflavanone:NADP⁺ 4-oxidoreductase

Comments:

This plant enzyme participates in the biosynthesis of the pterocarpan phytoalexins medicarpin, maackiain, and several forms of glyceollin. The enzyme has a strict stereo specificity for the 3R-isoflavanones.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 118477-70-6

References:

1.	Bless, W. and Barz, W. Isolation of pterocarpan synthase, the terminal enzyme of pterocarpan phytoalexin biosynthesis in cell-suspension cultures of Cicer arietinum. FEBS Lett. 235 (1988) 47–50.
2.	Guo, L., Dixon, R.A. and Paiva, N.L. Conversion of vestitone to medicarpin in alfalfa (Medicago sativa L.) is catalyzed by two independent enzymes. Identification, purification, and characterization of vestitone reductase and 7,2′-dihydroxy-4′-methoxyisoflavanol dehydratase. J. Biol. Chem. 269 (1994) 22372–22378. [PMID: 8071365]
3.	Guo, L., Dixon, R.A. and Paiva, N.L. The ‘pterocarpan synthase’ of alfalfa: association and co-induction of vestitone reductase and 7,2′-dihydroxy-4′-methoxy-isoflavanol (DMI) dehydratase, the two final enzymes in medicarpin biosynthesis. FEBS Lett. 356 (1994) 221–225. [DOI] [PMID: 7805842]
4.	Guo, L. and Paiva, N.L. Molecular cloning and expression of alfalfa (Medicago sativa L.) vestitone reductase, the penultimate enzyme in medicarpin biosynthesis. Arch. Biochem. Biophys. 320 (1995) 353–360. [DOI] [PMID: 7625843]
5.	Shao, H., Dixon, R.A. and Wang, X. Crystal structure of vestitone reductase from alfalfa (Medicago sativa L.). J. Mol. Biol. 369 (2007) 265–276. [DOI] [PMID: 17433362]

[EC 1.1.1.348 created 1992 as EC 1.1.1.246, part transferred 2013 to EC 1.1.1.348]

1.3.1.45

Accepted name:

2′-hydroxyisoflavone reductase

Reaction:

vestitone + NADP⁺ = 2′-hydroxyformononetin + NADPH + H⁺

For diagram of the biosynthesis of formononetin and derivatives, click here

Other name(s):

NADPH:2′-hydroxyisoflavone oxidoreductase; isoflavone reductase; 2′,7-dihydroxy-4′,5′-methylenedioxyisoflavone reductase

Systematic name:

vestitone:NADP⁺ oxidoreductase

Comments:

In the reverse reaction, a 2′-hydroxyisoflavone is reduced to an isoflavanone; 2′-hydroxypseudobaptigenin also acts. Involved in the biosynthesis of the pterocarpin phytoalexins medicarpin and maackiain.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 128449-69-4

References:

1.	Tiemann, K., Hinderer, W. and Barz, W. Isolation of NADPH:isoflavone oxidoreductase, a new enzyme of pterocarpan biosynthesis in cell suspensions of Cicer arietinum. FEBS Lett. 213 (1987) 324–328.

[EC 1.3.1.45 created 1990]

1.3.1.46

Accepted name:

biochanin-A reductase

Reaction:

dihydrobiochanin A + NADP⁺ = biochanin A + NADPH + H⁺

For diagram of the biosynthesis of biochanin A, click here

Systematic name:

dihydrobiochanin-A:NADP⁺ Δ²-oxidoreductase

Comments:

Some other isoflavones are reduced to the corresponding isoflavanones.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 112198-90-0

References:

1.	Tiemann, K., Hinderer, W. and Barz, W. Isolation of NADPH:isoflavone oxidoreductase, a new enzyme of pterocarpan biosynthesis in cell suspensions of Cicer arietinum. FEBS Lett. 213 (1987) 324–328.

[EC 1.3.1.46 created 1990]

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]

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]

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]

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, PDB

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]

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, PDB

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]

2.1.1.270

Accepted name:

(+)-6a-hydroxymaackiain 3-O-methyltransferase

Reaction:

S-adenosyl-L-methionine + (+)-6a-hydroxymaackiain = S-adenosyl-L-homocysteine + (+)-pisatin

Glossary:

(+)-6a-hydroxymaackiain = (6aR,12aR)-6H-[1,3]dioxolo[5,6][1]benzofuro[3,2-c]chromene-3,6a(12aH)-diol
(+)-pisatin = (6aR,12aR)-3-methoxy-6H-[1,3]dioxolo[5,6][1]benzofuro[3,2-c]chromen-6a(12aH)-ol

Other name(s):

HM3OMT; HMM2

Systematic name:

S-adenosyl-L-methionine:(+)-6a-hydroxymaackiain 3-O-methyltransferase

Comments:

The protein from the plant Pisum sativum (garden pea) methylates (+)-6a-hydroxymaackiain at the 3-position. It also methylates 2,7,4′-trihydroxyisoflavanone on the 4′-position (cf. EC 2.1.1.212, 2,7,4-trihydroxyisoflavanone 4-O-methyltransferase) with lower activity.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc

References:

1.	Preisig, C.L., Matthews, D.E. and Vanetten, H.D. Purification and characterization of S-adenosyl-L-methionine:6a-hydroxymaackiain 3-O-methyltransferase from Pisum sativum. Plant Physiol. 91 (1989) 559–566. [PMID: 16667069]
2.	Wu, Q., Preisig, C.L. and VanEtten, H.D. Isolation of the cDNAs encoding (+)6a-hydroxymaackiain 3-O-methyltransferase, the terminal step for the synthesis of the phytoalexin pisatin in Pisum sativum. Plant Mol. Biol. 35 (1997) 551–560. [PMID: 9349277]
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 2.1.1.270 created 2013]

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]

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, PDB, 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]

4.2.1.139

Accepted name:

pterocarpan synthase

Reaction:

a (4R)-4,2′-dihydroxyisoflavan = a pterocarpan + H₂O

For diagram of medicarpin and formononetin derivatives biosynthesis, click here

Glossary:

an isoflavan = an isoflavonoid with a 3,4-dihydro-3-aryl-2H-1-benzopyran skeleton.
(–)-medicarpin = (6aR,11aR)-9-methoxy-6a,11a-dihydro-6H-[1]benzofuro[3,2-c]chromen-3-ol
(+)-medicarpin = (6aS,11aS)-9-methoxy-6a,11a-dihydro-6H-[1]benzofuro[3,2-c]chromen-3-ol
(–)-maackiain = (6aR,12aR)-6a,12a-dihydro-6H-[1,3]dioxolo[5,6][1]benzofuro[3,2-c]chromen-3-ol
(+)-maackiain = (6aS,12aS)-6a,12a-dihydro-6H-[1,3]dioxolo[5,6][1]benzofuro[3,2-c]chromen-3-ol
(+)-pterocarpan = (6aR,11aR)-6a,11a-dihydro-6H-[1]benzofuran[3,2-c][1]benzopyran

Other name(s):

medicarpin synthase; medicarpan synthase; 7,2′-dihydroxy-4′-methoxyisoflavanol dehydratase; 2′,7-dihydroxy-4′-methoxyisoflavanol dehydratase; DMI dehydratase; DMID; 2′-hydroxyisoflavanol 4,2′-dehydratase; PTS (gene name); 4′-methoxyisoflavan-2′,4,7-triol hydro-lyase [(–)-medicarpin-forming]

Systematic name:

(4R)-4,2′-dihydroxyisoflavan hydro-lyase (pterocarpan-forming)

Comments:

The enzyme catalyses the formation of the additional ring in pterocarpan, the basic structure of phytoalexins produced by leguminous plants, including (–)-medicarpin, (+)-medicarpin, (–)-maackiain and (+)-maackiain. The enzyme requires that the hydroxyl group at C-4 of the substrate is in the (4R) configuration. The configuration of the hydrogen atom at C-3 determines whether the pterocarpan is the (+)- or (–)-enantiomer. The enzyme contains amino acid motifs characteristic of dirigent proteins.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB

References:

1.	Guo, L., Dixon, R.A. and Paiva, N.L. The ‘pterocarpan synthase’ of alfalfa: association and co-induction of vestitone reductase and 7,2′-dihydroxy-4′-methoxy-isoflavanol (DMI) dehydratase, the two final enzymes in medicarpin biosynthesis. FEBS Lett. 356 (1994) 221–225. [DOI] [PMID: 7805842]
2.	Guo, L., Dixon, R.A. and Paiva, N.L. Conversion of vestitone to medicarpin in alfalfa (Medicago sativa L.) is catalyzed by two independent enzymes. Identification, purification, and characterization of vestitone reductase and 7,2′-dihydroxy-4′-methoxyisoflavanol dehydratase. J. Biol. Chem. 269 (1994) 22372–22378. [PMID: 8071365]
3.	Uchida, K., Akashi, T. and Aoki, T. The missing link in leguminous pterocarpan biosynthesis is a dirigent domain-containing protein with isoflavanol dehydratase activity. Plant Cell Physiol. 58 (2017) 398–408. [PMID: 28394400]

[EC 4.2.1.139 created 2013, modified 2019]