p-Hydroxyphenylpyruvate dioxygenase is a herbicidal target site for beta-triketones from Leptospermum scoparium.
PHYTOCHEMISTRY 2007;
68:2004-14. [PMID:
17368492 DOI:
10.1016/j.phytochem.2007.01.026]
[Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Revised: 01/16/2007] [Accepted: 01/26/2007] [Indexed: 05/14/2023]
Abstract
p-Hydroxyphenylpyruvate dioxygenase (HPPD) is a key enzyme in tyrosine catabolism and is the molecular target site of beta-triketone pharmacophores used to treat hypertyrosinemia in humans. In plants, HPPD is involved in the biosynthesis of prenyl quinones and tocopherols, and is the target site of beta-triketone herbicides. The beta-triketone-rich essential oil of manuka (Leptospermum scoparium), and its components leptospermone, grandiflorone and flavesone were tested for their activity in whole-plant bioassays and for their potency against HPPD. The achlorophyllous phenotype of developing plants exposed to manuka oil or its purified beta-triketone components was similar to that of plants exposed to the synthetic HPPD inhibitor sulcotrione. The triketone-rich fraction and leptospermone were approximatively 10 times more active than that of the crude manuka oil, with I50 values of 1.45, 0.96 and 11.5 microg mL(-1), respectively. The effect of these samples on carotenoid levels was similar. Unlike their synthetic counterpart, steady-state O2 consumption experiments revealed that the natural triketones were competitive reversible inhibitors of HPPD. Dose-response curves against the enzyme activity of HPPD provided apparent I50 values 15.0, 4.02, 3.14, 0.22 microg mL(-1) for manuka oil, triketone-rich fraction, leptospermone and grandiflorone, respectively. Flavesone was not active. Structure-activity relationships indicate that the size and lipophilicity of the side-chain affected the potency of the compounds. Computational analysis of the catalytic domain of HPPD indicates that a lipophilic domain proximate from the Fe2+ favors the binding of ligands with lipophilic moieties.
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