Plant isoprenoid biosynthesis via the MEP pathway: In vivo IPP/DMAPP ratio produced by (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase in tobacco BY-2 cell cultures

Feeding tobacco BY-2 cells with [2-C-13, 4-H-2] deoxyxylulose revealed from the C-13 labeling that the plastid isoprenoids, synthesized via the MEP pathway, are essentially derived from the labeled precursor. The ca. 15% H-2 retention observed in all isoprene units corresponds to the isopentenyl diphosphate (IPP)/dimethylallyl diphosphate (DMAPP) ratio (85: 15) directly produced by the hydroxymethylbutenyl diphosphate reductase, the last enzyme of the MEP pathway. H-2 retention characterizes the isoprene units derived from the DMAPP branch, whereas H-2 loss represents the signature of the IPP branch. Taking into account the enantioselectivity of the reactions catalyzed by the (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase, the IPP isomerase and the transprenyl transferase, a single biogenetic scheme allows to interpret all labeling patterns observed in bacteria or plants upon incubation with H-2 labeled deoxyxylulose. (C) 2009 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.