Daidzein biosynthesis

HI4 OMT from G. echinata is thought to be distinct from the M. sativa lOMT, because a separate daidzein 7-OMT is present in G. echinata, prompting the suggestion that the lOMT be renamed D70MT. The HI4 OMT amino acid sequence is closely related to that of the SAM (+)-6a-hydroxymaackiain 3-(9-methyltransferase (HM30MT), which carries out a similar reaction in (+)-pisatin biosynthesis in Pisum sativum (pea) (see Section 3.9.7). The... 

Akashi, T. et al.. New scheme of the biosynthesis of formononetin involving 2,7,4 -trihydroxyiso-flavanone but not daidzein as the methyl acceptor. Biosci. BiotechnoL Biochem., 64, 2276, 2000. 

Liu, C.J. and Dixon, R.A., Elicitor-induced association of isofiavone 0-methyltransferase with endomembranes prevents the formation and 7-0-methylation of daidzein during isofiavonoid phytoalexin biosynthesis. Plant Cell, 13, 2643, 2001. 

Microsomal preparations from yeast-elicited cell cultures of chickpea catalyzed the hydroxylation of formononetin and biochanin A to their 2 - and 3 -hydroxy derivatives.43 44 Neither daidzein nor genistein were accepted as substrates. Both hydroxylation reactions seem to be catalyzed by two distinct enzymes, since they exhibited different physicochemical properties and induction kinetics in cell cultures and roots of chickpeas.45 Both 2 - and 3 -hydroxylations of formononetin are prerequisite reactions in the pathway for biosynthesis of the phytoalexins, medicarpin and maackiain in alfalfa and chickpea, respectively8. 

Figure 38.2 Possible sites of inhibitory actions of soy isoflavones on iodine utilization and thyroid hormone biosynthesis and actions. Soy isoflavonoids, genistein and daidzein, inhibit oxidation of iodide by thyroid peroxidase at the apical membrane of thyroid follicular cells, followed by iodination of tyrosine residues in thyroglobulin and their coupling in colloid. In addition, they may affect deiodination of iodothyronines and interfere with thyroid hormone binding to transthyretin. Full arrows indicate the sites of inhibition. So far, only few reports concern the effect of thyroid hormone actions in target cells.

Figure 14. Biosynthesis of equol (49) via daidzein (6) from formononetin (42) or via genistein (5) from biochanin A (41).

The precursors of flavonoid biosynthesis include shikimic acid, phenylalanine, cinnamic acid, and p-coumaric acid. Shikimic acid acts as an intermediate in the biosynthesis of aromatic acid. The basic pathways to the core isoflavonoid skeletons have been established both enzymatically and genetically [16]. The synthesis of isoflavones can be broadly divided into three main synthetic pathways the formylation of deoxybenzoins, the oxidative rearrangement of chalcones and flavanones, and the arylation of a preformed chromanone ring. In leguminous plants, the major isoflavonoids are produced via two branches of the isoflavonoid biosynthetic pathway, and the different branches share a majority of common reactions [1]. Unlike the common flavonoid compotmds, which have a 2-phenyl-benzopyrone core structure, isoflavones, such as daidzein and genistein, are 3-phenyl-benzopyrone compounds. Biochemically, the synthesis of isoflavones is an offshoot of the flavonoids biosynthesis pathway. Several attempts have aimed to increase... 

The use of sterile germinating seeds of Amorpha fruticosa has provided further information on the biosynthesis of amorphigenin(l 16). Administration of labelled 2, 4,4 -trihydroxychalcone (108), 7-hydroxy-4 -methoxyisoflavone (109 R = Me, formononetin), 7-hydroxy-2, 4, 5 -trimethoxyisoflavone (110), 9-methyImunduserone (111), rotenonic acid (112), or rotenone (115) to the seed system resulted in efficient conversion into amorphigenin (116), and the outline of a biosynthetic scheme for this compound has been proposed (Scheme 19). Of considerable interest was the fact that 7,4 -dihydroxyisollavone (109 R = H, daidzein) was not an efficient precursor, and this has been cited as... 

Biosynthesis of HydroxyphaseoUin.—The biosynthesis of a newly discovered pterocarpan (48)" has been investigated in disease-resistant soya bean hypo-cotyls. [U- C]Phenylalanine and [9- C]isoliquiritigenin were readily incorporated into (48). Label also appeared in daidzein, coumestrol, and spjagol (49). The biosynthetic pathway followed the generally expected route... 

---