title: A systems biology approach identifies the biochemical mechanisms regulating monoterpenoid essential oil composition in peppermint.
abstract: The integration of mathematical modeling and experimental testing is emerging as a powerful approach for improving our understanding of the regulation of metabolic pathways. In this study, we report on the development of a kinetic mathematical model that accurately simulates the developmental patterns of monoterpenoid essential oil accumulation in peppermint (Mentha x piperita). This model was then used to evaluate the biochemical processes underlying experimentally determined changes in the monoterpene pathway under low ambient-light intensities, which led to an accumulation of the branchpoint intermediate (+)-pulegone and the side product (+)-menthofuran. Our simulations indicated that the environmentally regulated changes in monoterpene profiles could only be explained when, in addition to effects on biosynthetic enzyme activities, as yet unidentified inhibitory effects of (+)-menthofuran on the branchpoint enzyme pulegone reductase (PR) were assumed. Subsequent in vitro analyses with recombinant protein confirmed that (+)-menthofuran acts as a weak competitive inhibitor of PR (K(i) = 300 muM). To evaluate whether the intracellular concentration of (+)-menthofuran was high enough for PR inhibition in vivo, we isolated essential oil-synthesizing secretory cells from peppermint leaves and subjected them to steam distillations. When peppermint plants were grown under low-light conditions, (+)-menthofuran was selectively retained in secretory cells and accumulated to very high levels (up to 20 mM), whereas under regular growth conditions, (+)-menthofuran levels remained very low (<400 muM). These results illustrate the utility of iterative cycles of mathematical modeling and experimental testing to elucidate the mechanisms controlling flux through metabolic pathways.
authors.affiliation: Institute of Biological Chemistry, M. J. Murdock Metabolomics Laboratory, Center for Integrated Biotechnology, and School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6340, USA.
authors.forename: Rigoberto
authors.initials: R
authors.lastname: Rios-Estepa
authors.forename: Glenn W
authors.initials: GW
authors.lastname: Turner
authors.forename: James M
authors.initials: JM
authors.lastname: Lee
authors.forename: Rodney B
authors.initials: RB
authors.lastname: Croteau
authors.forename: B Markus
authors.initials: BM
authors.lastname: Lange
mesh_terms: D053898:Biosynthetic Pathways / Q000502:physiology*; D003198:Computer Simulation; D000081005:Cyclohexane Monoterpenes; D007700:Kinetics; D036142:Mentha piperita / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D039821:Monoterpenes / Q000032:analysis / Q000378:metabolism*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010938:Plant Oils / Q000737:chemistry*; D049490:Systems Biology / Q000379:methods*
chemical_list: D000081005:Cyclohexane Monoterpenes; D039821:Monoterpenes; D010938:Plant Oils; C054487:menthofuran; C039648:pulegone; C015424:peppermint oil; D010088:Oxidoreductases; C480901:pulegone reductase