Vestitone reductase

Based on analysis of enzyme preparations, the conversion of isoflavanones to pterocarpans was thought initially to be catalyzed by a single NADPH-dependent enzyme, termed the pterocarpan synthase (PTS). However, it was subsequently shown that in M. sativa the conversion of vestitone to medicarpin involves two enzymes, VR and 7,2 -dihydroxy-4 -methoxyisoflavanol (DMI) dehydratase (DMID). The reaction series from vestitone to the pterocarpan is thought to proceed by the VR-catalyzed reduction of vestitone to DMI, followed by the loss of water and formation of the C-O-C bridge between the heterocycle and the B-ring, catalyzed by DMID. 

Guo and Paiva used the amino acid sequence of purified VR to isolate a cDNA clone from M. sativa, which was then analyzed by expression in E. coli. VR, a monomeric 38 kDa 

In some species, such as C. arietinum and M. saliva, the products of VR and DMID (maackiain and medicarpin) are the main pterocarpan phytoalexins. They are typically glucosylated and malonylated and stored in the vacuole. In species such as G. max, P. sativum, and P. vulgaris, the pterocarpans are further converted by a series of reactions to species-specific compounds. For G. max and P. sativum, the initial reaction is a hydro-xylation catalyzed by P6aH. 

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DFR belongs to the single-domain-reductase/epimerase/dehydrogenase (RED) protein family, which has also been termed the short chain dehydrogenase/reductase (SDR) superfamily. This contains other flavonoid biosynthetic enzymes, in particular the anthocyanidin reductase (ANR), leucoanthocyanidin reductase (EAR), isoflavone reductase (IFR), and vestitone reductase (VR), as well as mammalian, bacterial, and other plant enzymes. ... 

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, 22372, 1994. 

Guo L, Dixon RA, Paiva NL. 1994b. 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 356 221-225. 

Lopez-Meyer M, Paiva NL. 2002. Immunolocalization of vestitone reductase and isoflavone reductase, two enzymes involved in the biosynthesis of the phytoalexin medicarpin. Physiol Molec Plant Pathol 61 15-30. 

Chalcone synthase (CHS) and chalcone reductase (CHR) convert 4-coumaro-yl-CoA (15) and 3 mol malonyl-CoA (16) to trihydroxychalcone (a chalcone) (17) via tetrahydroxychalcone (a chalcone) (18). Chalcone isomerase (CHI) converts trihydroxychalcone (a chalcone) (17) into liquiritigenin (7,4/-dihydroxyllavanone, a flavanone) (19). Isoflavone synthase (IFS) converted flavanone (19) to isoflavones (20) such as daidzein (21) and genis-tein (22). Isoflavone 2/-hydroxylase (I2 H) hydroxylated isoflavones (20) to 4/-methoxyisoflavones (23). Isoflavone 2 -hydroxylase (I2 H) hydroxylated 4/-methoxyisoflavones (23) into 2/-hydroxy-4/-methoxyisoflavones (24). Isoflavone reductase (IFR) reduced 2/-hydroxy-4/-methoxyisoflavones (24) to 2/-hydroxy-4/-methoxyisoflavonones (25). Finally, vestitone reductase (VR) and 4/-methoxyisoflavanol dehydrogenase (DMID) cyclized 2/-hydroxy-4/-methoxyisoflavonones (25) to form isoflavonoids (26) such as medicarpin (27) (Fig. 4) [23,24]. 

Fig. 2.6 An overview of isoflavonoid biosynthesis in the Leguminosae based on recent findings. Partially characterized or uncertain steps are shown by the dotted arrows. 2HIS, 2-hydroxyisoflavanone synthase 2 OMT, 2 -0-methyltransferase (presumed) DMID, 7,2 -dihydroxy-4 -methoxyisoflavanol dehydratase HI4 OMT, hydroxyiso-flavanone 4 -0-methyltransferase I2 H, isoflavone 2 -hydroxylase IFR, isoflavone reductase PTR, pterocarpan reductase VR, vestitone reductase.

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