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Rapid Regulation of the Methylerythritol 4-Phosphate Pathway during Isoprene Synthesis¹

Institut für Angewandte Physik, Universität Bonn, D–53115 Bonn, Germany (M.W., F.K.); Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (T.D.S.); and Max-Planck-Institut für Chemische Ökologie, D–07745 Jena, Germany (W.B.)

More volatile organic carbon is lost from plants as isoprene than any other molecule. This flux of carbon to the atmosphere affects atmospheric chemistry and can serve as a substrate for ozone production in polluted air. Isoprene synthesis may help leaves cope with heatflecks and active oxygen species. Isoprene synthase, an enzyme related to monoterpene synthases, converts dimethylallyl diphosphate derived from the methylerythritol 4-phosphate pathway to isoprene. We used dideuterated deoxyxylulose (DOX-d₂) to study the regulation of the isoprene biosynthetic pathway. Exogenous DOX-d₂ displaced endogenous sources of carbon for isoprene synthesis without increasing the overall rate of isoprene synthesis. However, at higher concentrations, DOX-d₂ completely suppressed isoprene synthesis from endogenous sources and increased the overall rate of isoprene synthesis. We interpret these results to indicate strong feedback control of deoxyxylulose-5-phosphate synthase. We related the emission of labeled isoprene to the concentration of labeled dimethylallyl diphosphate in order to estimate the in situ K_m of isoprene synthase. The results confirm that isoprene synthase has a K_m 10- to 100-fold higher for its allylic diphosphate substrate than related monoterpene synthases for geranyl diphosphate.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.043737.

^* Corresponding author; e-mail tsharkey{at}wisc.edu; fax 608–262–7509.

Received March 29, 2004; returned for revision May 25, 2004; accepted May 26, 2004.

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