Isoflavone 2 -hydroxylase

CLEMENS, S., HINDERER, W WITTKAMPF, U BARZ, W Characterization of cytochrome P450-dependent isoflavone hydroxylases from chickpea. Phytochemistry, 1993,32,653-657. 

Figure 5.4. Abbreviated scheme for biosynthesis of major flavonoid subclasses, showing the primary enzymes and substrates leading to different subclasses. Bold-faced, uppercase abbreviations refer to enzyme names, whereas substrate names are presented in lowercase letters. PAL, phenylalanine ammonia lyase C4H, cinnamate 4-hydroxylase 4CL, 4-coumarate CoA ligase CHS, chalcone synthase CHI, chalcone isomerase CHR, chalcone reductase IPS, isoflavone synthase F3H, flavonone 3-hydroxylase F3 H, flavonoid 3 -hydroxylase F3 5 H, flavonoid 3 5 -hydroxylase FNSI/II, flavone synthase DFR, dihydroflavonol 4-reductase FLS, flavonol synthase ANS, anthocyanidin synthase LAR, leucoanthocyanidin reductase ANR, anthocyanidin reductase UFGT, UDP-glucose flavonoid 3-O-glucosyltransferase. R3 = H or OH. R5 = H or OH. Glc = glucose. Please refer to text for more information.

Figure 1.36 Schematic diagram of the stilbene and flavonoid biosynthetic pathway. Enzyme abbreviations SS, stilbene synthase CHS, chalcone synthase CHR, chalcone reductase CHI, chalcone isomerase IFS, isoflavone synthase FNS, flavone synthase F3H, flavanone 3-hydroxylase FLS, flavonol synthase F3 H, flavonoid 3 -hydroxylase DFR, dihydroflavonol 4-reductase LAR, leucoanthocyanidin 4-reductase LDOX, leucocyanidin deoxygenase ANR, anthocyanidin reductase EU, extension units TU, terminal unit.

Hinderer W, Flentje U, Barz W. 1987. Microsomal isoflavone 2- and 3-hydroxylases from chickpea (Cicer arietinum L.) cell suspensions induced for pterocarpan phytoalexin formation. FEBS Lett 214 101-106. 

Scheme 1.1 Pathway for the biosynthesis of the major classes of flavonoids. 1, Chalcone synthase 2, chalcone isomerase 3, flavone synthase 4, flavanone 3-hydroxylase 5, flavonol synthase 6, dihydroflavonol reductase 7, anthocyanidin synthase 8, anthocyanidin glucosyltransferase 9, chalcone-ketide reductase 10, chalcone isomerase 11, isoflavone synthase 12, isoflavone 2 -hydroxylase 13, isoflavone reductase 14, pterocarpan synthase 15, pterocarpan 6a-hydroxylase 16, prenyltransferase 17, prenylcyclase.

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]. 

CHS, chalcone. synthase CHI, chalcone isomerase IFS+IFD, 2-hydroxyisoflavanone synthase + dehydratase IOMT, Isoflavone 4 -0-methyI transferase FLH, flavone 3-hydroxylase FLS, flavonol synthase... 

IFH, isoflavone 2 -hydroxylase IFR, isoflavone reductase PIS, pterocarpan synthase... 

For these reasons, we attempted to increase the levels of isoflavones in soybean. By combining expression of a chimeric transcription factor (CRC), which acts to increase flux through the phenylpropanoid pathway with the suppression of a competing pathway via RNAi mediated silencing of flavanone 3-hydroxylase, levels of isoflavones were shown to accumulate in the seed to levels that were 3-4 times higher than in wild type soybeans. 

Oxygenation at the 2 -position of isoflavones is requisite for formation of pterocarpans. 2 -Hydroxylases (as well as... 

Akashi T, Aoki T, Ayabe S (1998a) CYP81E1, a cytochrome P450 cDNA of licorice Gfycyrrhiza echinata L.), encodes isoflavone 2 -hydroxylase. Biochem Biophys Res Commun 251 67-70... 

Li Y, Mezei O, Shay NF (2007) Human and murine hepatic sterol-12a-hydroxylase and other xe-nobiotic metabolism mRNA are upiegulated by soy isoflavones. JNutr 137 1705-1712... 

PAL - phenylalanine ammonia lyase TAL -tyrosine ammonia lyase C4H - dnnamate 4-hydroxylase 4CL - 4-coumarate-CoA ligase STS - stilbene synthase CUS - curcuminoid synthase CHS - chalcone synthase CHI - chalcone isomerase IPS - isoflavone synthase FSI - soluble flavone synthase FSII - membrane-bound flavone synthase... 

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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