title: The phytotoxic lichen metabolite, usnic acid, is a potent inhibitor of plant p-hydroxyphenylpyruvate dioxygenase.
abstract: The lichen secondary metabolite usnic acid exists as a (-) and a (+) enantiomer, indicating a alpha or beta projection of the methyl group at position 9b, respectively. (-)-Usnic caused a dose-dependent bleaching of the cotyledonary tissues associated with a decrease of both chlorophylls and carotenoids in treated plants whereas no bleaching was observed with the (+) enantiomer. (-)-Usnic acid inhibited protophorphyrinogen oxidase activity (I50 = 3 microM), but did not lead to protoporphyrin IX accumulation. Bleaching appears to be caused by irreversible inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase by (-)-usnic acid (apparent IC50 = 50 nM).
authors.affiliation: USDA/ARS, Natural Products Utilization Research Unit, University of Mississippi, Lafayette Co 38677, USA. romagnj@stthom.edu
authors.forename: J G
authors.initials: JG
authors.lastname: Romagni
authors.forename: G
authors.initials: G
authors.lastname: Meazza
authors.forename: N P
authors.initials: NP
authors.lastname: Nanayakkara
authors.forename: F E
authors.initials: FE
authors.lastname: Dayan
mesh_terms: D015111:4-Hydroxyphenylpyruvate Dioxygenase / Q000037:antagonists & inhibitors*; D001572:Benzofurans / Q000737:chemistry / Q000494:pharmacology*; D002338:Carotenoids / Q000096:biosynthesis; D002734:Chlorophyll / Q000378:metabolism; D018548:Cotyledon / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D008011:Lichens; D015394:Molecular Structure
chemical_list: D001572:Benzofurans; D004791:Enzyme Inhibitors; C073339:usnic acid; D002734:Chlorophyll; D002338:Carotenoids; D015111:4-Hydroxyphenylpyruvate Dioxygenase