Isoflavone, 9-methyltransferase

An isoflavone (9-methyltransferase from elicitor-treated cell suspension cultures of Medicago sativa exhibited activity with 6,7,4 -trihydroxyisoflavone (85), as well as a number of other isoflavones, isoflavans, and pterocarpans (Edwards and Dixon, 1991). Both a 4 -(9-methyltransferase and a 7-0-methyltransferase occur (Barz and Welle, 1992). 

He X-Z, Dixon RA. 2000. Genetic manipulation of isoflavone 7-O-methyltransferase enhances biosynthesis of 4 -0-methylated isoflavonoid phytoalexins and disease resistance in alfalfa. Plant Cell 12 1689-1702. 

KHOURI, H.E., TAHARA, S., IBRAHIM, R.K., Partial purification, characterization and kinetic analysis of isoflavone 5-O-methyltransferase from yellow lupin roots. Arch. Biochem. Biophys., 1988,262,592-598. 

HE, X.-E., REDDY, J.T., DIXON, R.A., Stress responses in alfalfa (Medicago saliva L.). XXII. cDNA cloning and characterization of an elicitor-inducible isoflavone 7-O-methyltransferase. Plant Mol. Biol., 1998,36,43-54. 

HE, X.Z., DIXON, R.A., Affinity chromatography, substrate/product specificity, and amino acid sequence analysis of an isoflavone O-methyltransferase from alfalfa (Medicago sativa L.), Arch. Biochem. Biophys., 1996,336,121-129. 

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. 

Liu, C.J. and R.A. Dixon (2001). Elicitor-induced association of isoflavone O-methyltransferase with endomembranes prevents the formation of 7-0-methylation of daidzein during isoflavonoid phytoalexins biosynthesis. Plant Cell 13, 2643-2658. 

Edwards, R. and R. A. Dixon, Isoflavone G-methyltransferase activities in elicitor-treated cell suspension cultures of Med-icago sativa. Phytochemistry, 30, 2597-2606 (1991). 

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.

Fig. 2.7 Recent progress in the characterization of the biosynthetic pathway to (+)-pisatin in the pea, Pisum sativum. HMM, (+)-6a-hydroxymaacldain 3-0-methyltransferase IFR, isoflavone reductase SOR, sophorol reductase.

Deavouis, B.E. etal. (2006) Functional analysis of members of the isoflavone and isofla-vanone O-methyltransferase enzyme families from the model legume Medicago truncatula. Plant Mol. Biol. 62, 715-733... 

Fig. 4 Architecture of the chalcone O-methyltransferase isoflavone (a) and O-methyltransferase (lOMT) (b) active sites. Structural analysis shows that the tertiary structures of these enzymes are highly conserved substrate selectivity is determined by variations in side chains on the active site surface that alter van der Walls interactions and hydrogen bonding patterns (From [32])...

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