Partially methylated flavonols

GAUTHIER, A., GULICK, PJ., IBRAHIM, R.K., cDNA cloning and characterization of a 3 /5 -0-methyltransferase for partially methylated flavonols from Chrysosplenium americanum. Plant Mol. Biol., 1996,32,1163-1169. 

Regulation of Flavonoid Synthesis in C. americanum. Biosynthesis of methylated flavonol glucosides seems to be under tight regulation, not only by the substrate specificity of the enzymes involved, but also by other factors, among which are (a) the strict position specificity of these enzymes towards their hydroxylated or partially methylated substrates (b) the apparent difference in microenvironment of the different methyl-transferases, whereby those earlier in the pathway utilized aglycones whereas later enzymes accepted only glucosides as substrates (c) the subtle characteristic differences in methyl-transferases with respect to their pH optima, pi values and requirement for Mg ions, despite their similar molecular size ... 

The F6H showed low activity against flavones and little action on the flavonol kaemp-ferol. Nevertheless, it is possible that a similar biosynthetic route through hydroxylation of precursors, perhaps by the same F6H, is involved in the production of other 6-hydroxyfla-vonoids. However, an alternative activity of the 20GD type has been characterized at the biochemical level from C. americanum that catalyzes the 6-hydroxylation of partially methylated flavonoids. ... 

KHOURI, H.E., ISHIKURA, N., IBRAHIM, R.K., Fast protein liquid chromatographic purification and some properties of a partially 0-methylated flavonol glucoside 2 -/5 -0-methyltransferase. Phytochemistry, 1986, 25, 2475-2479. 

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