Isoflavone synthase

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.

While fiavonoids have the 2-phenylchromen-4-one backbone, isoflavonoids (Fig. 8) have the 3-phenylchromen-4-one backbone, with no hydroxyl substitution at position 2 in the case of isofiavones. In contrast with the parent class of fiavonoids, the distribution of the isoflavonoid class in the plant kingdom is relatively limited, probably owing to the sporadic occurrence of isoflavone synthase. Isoflavonoids... 

Flydroxyisoflavanone synthase (isoflavone synthase) 2HIS (IFS) 5.4.99.- CytP450 (CYP93C) 180-182... 

Subramanian, S. et al., The promoters of the isoflavone synthase genes respond differentially to nodulation and defense signals in transgenic soybean roots. Plant Mol. Biol, 54, 623, 2004. 

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.

Jung W, Yu O, Lau S-M C, O Keefe DP, Odell J, Fader G, McGonigle B. 2000. Identification and expression of Isoflavone synthase, the key enzyme for biosynthesis of isoflavones in legumes. Nature 18 208-212. 

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]. 

Figure 6.53. Isoflavone synthase (CYP93C) catalyzes the formation of isoflavone from 25 -flavone via an oxidative aryl migration. A possible mechanism involving an anchimerically stabilized radical is shown.

In all cases, the unique aryl migration reaction to create the isoflavones is mediated by 2-hydroxyisoflavanone synthase, also known as isoflavone synthase (IFS). Sequences encoding the IFS gene have been identified, and the encoded... 

Shih CH, Chen Y, Wang M, Chu IK, Lo C (2008) Accumulation of isoflavone genistin in transgenic tomato plants oveiexpressing a soybean isoflavone synthase gene. J Agric Food Chem 56 5655-5661... 

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... 

Kim DH, Kim B-G, Jung NR, Ahn J-H (2(X)9) Production of genistein from naringenin using Escherichia coli containing isoflavone synthase-cytochrome P450 reductase fusion protein. J Microbiol Biotechnol 19 1612-1616... 

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