Isoflavones phenylpropanoid pathway

Root flavonoids that may act as signals for the initiation and development of endomycorrhizal and ectomycorrhizal symbio.ses have been identified (see Chap. 7). Metabolites of the phenylpropanoid pathways apparently act as signaling molecules in endo- and ectomycorrhizal interactions (14). The role of flavonoids is still controversial, but a variety of flavanones, flavones, and isoflavones... 

Fig. 4 Biosynthesis of isoflavonoids (pterocarpans) via isoflavones from phenylpropanoid pathway...

Figure 8.2 A partial diagram of the phenylpropanoid pathway. Intermediates and en7ymcs involved in isoflavone synthesis, as well as some branch pathways, are shown. Dashed airow.s represent multiple steps the dotted arrow represents a speculative step.

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. 

The understanding of the degradation of natural products such as camphor has been greatly enhanced by understanding the catalytic cycle of the cytochrome P-450 enzyme P-450cam in structural detail.3,4 These enzymes catalyze the addition of 02 to nonactivated hydrocarbons at room temperatures and pressures - a reaction that requires high temperature to proceed in the absence of a catalyst. O-Methyltransferases are central to the secondary metabolic pathway of phenylpropanoid biosynthesis. The structural basis of the diverse substrate specificities of such enzymes has been studied by solving the crystal structures of chalcone O-methyltransferase and isoflavone O-methyltransferase complexed with the reaction products.5 Structures of these and other enzymes are obviously important for the development of biomimetic and thus environmentally more friendly approaches to natural product synthesis. 

Isoflavones are synthesized as one group of end-products (iso-flavones) in the phenylpropanoid biosynthetic pathway (Fig. 60.5). They occur in highest levels in the roots, developing seedlings, and seeds of leguminous plants, but are found in lower amounts in leaves, stems, roots, and flowers of older plants. In seeds, they are... 

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