Dimethylallylpyrophosphate DMAPP pathway

Dimethylallylpyrophosphate (DMAPP) originating from cytosolic mevalonate (JVIVA) pathway probably serves as a precursor of tRNA isoprenylation [80]. Release of cytokinins via tRNA degradation could at least serve as a possible source of cA-zeatin, which is much more abundant in RNA than the tran5-isomer [89] and further de novo biosynthesis of this cytokinin species [90] as well as its isomerization from trans-xQ-dim have not been proved yet. 

The biosynthesis of the furan moiety was investigated for skimmianine, a dictamnine-related alkaloid, using Fagara coco (Rutaceae). Thus, when C-4- or C-5-labeled 3R-mevalonic acid was used in the biosynthetic pathway, C-labeled skimmianine was observed in both cases. When the labeled skimmianine was degraded, radioactive skimmianic acid was obtained from C-4-labeled 3R-mevalonic acid, but radioinactive skimmianic acid was obtained when C-5-labeled 3R-mevalonic acid was fed. Consequently, it was concluded that the C-T and C-2 carbons (furan moiety) of skimmianine were derived from the C-5 and C-4 carbons of mevalonic acid, respectively [4].The biosynthetic precursor of dictamnine is therefore a quinoline alkaloid with a prenyl moiety, derived from dimethylallylpyrophosphate (DMAPP), at the C-3 position, such as platy-desmine [5]. It was also shown that the methyl carbon of the methoxyl moiety at the C-4 position of skimmianine was derived from methionine. 

Fig. 95.1 Terpene biosynthesis pathways and their subcellular localization in the plants. Different classes of terpenes are respectively formed in the cytosol or the plastid by two independent pathways in the plants, that is, acetate-mevalonate pathway (MEV) (cytosol) and methylerythritol 4-phosphate (MEP) or deoxyxylulose 5-phosphate pathway (DXP) (plastid). Mraioterpcmes, diterpenes, and tetraterpenes are derived from IPP and DMAPP Irran the plastidial MEP ot DXP pathway. Sesquiterpenes and triterpenes are biosynthesized from IPP and DMAPP from the cytosol pathway. Black square with a white question mark suggests a possible transport of IPP (isopentenylpyrophosphate) from the plastid to the cytosol. Other metabolites involved in the different steps are DMAPP dimethylallylpyrophosphate, FPP famesylpyrophosphate, GASP D- glyceraldehyde- 3-phosphate, GPP geranylpyrophosphate, GGPP geranylgeranylpyro-phosphate. TPSs in the circle correspond to terpene synthases. Broken arrows show several enzymatic steps (Adapted from Aharoni et al. [8] and Sallaud et al. [154])...

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