Hydroxyisoflavanone synthase

Akashi et al. suggested that the 2-hydroxyisoflavanone product of 2HIS (e.g., 2,7,4 -trihydroxyisoflavanone that dehydrates to daidzein) might be the substrate for the 4 -(9-methylation reaction in vivo, rather than daidzein itself. This biosynthetic route is 

FIGURE 3.5 Biosynthetic route to isoflavonoids (and some derivatives) from the 5-deoxyflavanone liquiritigenin. A possible route to the retrochalcone echinatin is also shown. Unlabelled arrows indicate biosynthetic steps for which the enzyme(s) have not been characterized. Enzyme abbreviations are defined in the text and in Table 3.1, except for P2CP, pterocarpan 2-C-prenyltransferase P4CP, pterocarpan 4-C-prenyltransferase. 

FIGURE 3.6 Biosynthetic route to isoflavones from the 5-hydroxyflavanone naringenin. Enz5me abbreviations are defined in the text. 

An alternative biosynthetic route for the introduction of the 4 -methoxyl has been suggested from studies of M. sativa. Initial studies of one of the four isoflavone OMTs (lOMTs) of M. sativa showed it had 7-0-methylation activity to the A-ring of daidzein, thus forming isoformononetin from daidzein. However, overexpression of this lOMT in transgenic 

sativa plants enhanced the biosynthesis of 4 -0-methylated isoflavonoids. 

---

Figure 8.5 Phenylpropanoid biosynthetic pathway. IFS 2-hydroxyisoflavanone synthase F2H flavanone-2-hydroxylase F3 5 H flavnonoid-3 ,5 -hydroxylase...

AKASHI, T., AOKI, T., AYABE, S., Cloning and functional expression of a cytochrome P450 cDNA encoding 2-hydroxyisoflavanone synthase involved in biosynthesis of the isoflavonoid skeleton in licorice, Plant Physiol., 1999,121, 821-828. 

Sawada, Y. et al.. Key amino acid residues required for aryl migration catalysed by the cytochrome P450 2-hydroxyisoflavanone synthase. Plant J., 31, 555, 2002. 

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... 

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... 

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.

---