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Title:   Author  item
                                            Dayan, Franckitem
                                            Duke, Stephenitem
                                            SAULDUBOIS, AUDREY - UNIV. OF ANGERS-FRANCEitem
                                            SINGH, NIDHI - UNIVERSITY OF MISSISSIPPIitem
                                            MCCURDY, CHRIS - UNIVERSITY OF MISSISSIPPIitem
                                            Cantrell, Charles
  Submitted to: Phytochemistry
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/16/2007
                                    Publication  Date: 3/26/2007
                                    Citation: Dayan, F.E., Duke, S.O., Sauldubois, A., Singh, N., Mccurdy, C., Cantrell, C.L. 2007. p-Hydroxyphenylpyruvate Dioxygenase is a Herbicidal Target Site for B-triketones from Leptospermum Scoparium. Phytochemistry. 68:2004-2014.Interpretive Summary: The enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD) catalyzes important reaction in plants.  It is responsible for the biosynthesis of prenyl quinones and tocopherol, and is the target site a class of herbicides.  The 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.  Plants exposed to manuka oil or its purified components had symptoms similar to that of plants treated with a conventional synthetic inhibitor of this enzyme.  The relative inhibitory activities on the enzyme were grandiflorone > leptospermone > flavesone.  The herbicidal activity of the semi-purified oil may be sufficient to be used as a natural herbicide.
                                Technical Abstract: p-Hydroxyphenylpyruvate dioxygenase (HPPD) is a key enzyme in tyrosine catabolism and is the molecular target site of B-triketone pharmacophores used to treat hypertyrosinemia in humans.  In plants, HPPD is involved in the biosynthesis of prenyl quinones and tocopherol, and is the target site of B-triketone herbicides.  The B-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 phenotype of developing plants exposed to manuka oil or its purified B-triketone components was similar to that of plants exposed to a synthetic HPPD inhibitor.  Chlorophyll and carotenoid levels decreased in a dose-dependent manner upon inhibition of HPPD.  Unlike their synthetic counterpart, steady-state O2 consumption experiments revealed that the natural triketones behaved as competitive reversible inhibitors of HPPD, with the relative inhibitory activities of grandiflorone > leptospermone > flavesone.  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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