The Roles of a Flavone-6-Hydroxylase and 7-O-Demethylation in the Flavone Biosynthetic Network of Sweet Basil |
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Authors: | Anna Berim David R Gang |
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Institution: | From the Institute of Biological Chemistry Washington State University, Pullman, Washington 99164-6340 |
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Abstract: | Lipophilic flavonoids found in the Lamiaceae exhibit unusual 6- and 8-hydroxylations whose enzymatic basis is unknown. We show that crude protein extracts from peltate trichomes of sweet basil (Ocimum basilicum L.) cultivars readily hydroxylate position 6 of 7-O-methylated apigenin but not apigenin itself. The responsible protein was identified as a P450 monooxygenase from the CYP82 family, a family not previously reported to be involved in flavonoid metabolism. This enzyme prefers flavones but also accepts flavanones in vitro and requires a 5-hydroxyl in addition to a 7-methoxyl residue on the substrate. A peppermint (Mentha × piperita L.) homolog displayed identical substrate requirements, suggesting that early 7-O-methylation of flavones might be common in the Lamiaceae. This hypothesis is further substantiated by the pioneering discovery of 2-oxoglutarate-dependent flavone demethylase activity in basil, which explains the accumulation of 7-O-demethylated flavone nevadensin. |
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Keywords: | Cytochrome P450 Dioxygenase Hydroxylase Metabolism Secondary Metabolism O-Demethylation Basil Lipophilic Flavones |
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