title: The roles of a flavone-6-hydroxylase and 7-O-demethylation in the flavone biosynthetic network of sweet basil.
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.
authors.affiliation: Institute of Biological Chemistry Washington State University, Pullman, Washington 99164-6340, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Berim
authors.forename: David R
authors.initials: DR
authors.lastname: Gang
mesh_terms: D000595:Amino Acid Sequence; D047310:Apigenin / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D044950:Flavanones / Q000378:metabolism; D047309:Flavones / Q000378:metabolism*; D013058:Mass Spectrometry; D036142:Mentha piperita / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018649:Ocimum basilicum / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D010936:Plant Extracts / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D044950:Flavanones; D047309:Flavones; D010936:Plant Extracts; D010940:Plant Proteins; C023982:nevadensin; D047310:Apigenin; D003577:Cytochrome P-450 Enzyme System; C423312:flavonoid 6-hydroxylase