EC 4.2.1.139     
Accepted name: pterocarpan synthase
Reaction: a (4R)-4,2′-dihydroxyisoflavan = a pterocarpan + H2O
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.
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. [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]