The roles of a flavone 6-hydroxylase and 7-O-demethylation in the flavone biosynthetic network of sweet basil.
OPEN The Journal of biological chemistry | 28 Nov 2012
A Berim and DR Gang
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 x piperita) 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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