Isopentyl diphosphate

FIGURE 3.1 Main classes of secondary metabolites. Fatty acids and acetogenins are derived from acetyl Coenzyme A, which forms the isopentyl diphosphate that forms terpenes. The (unusual) polypropionates derive from propionyl CoA. Alkaloids are typically modified amino acids. 

All carotenoids are derived from the isoprenoid or terpenoid pathway. From prenyl diphosphates of different chain lengths, specific routes branch off into various terpenoid end products. The prenyl diphosphates are formed by different prenyl transferases after isomerization of IPP to DMAPP by successive T-4 condensations with IPP molecules. Condensation of one molecule of dimethylallyl diphosphate (DMADP) and three molecules of isopentyl diphosphate (IDP) produces the diter-pene geranylgeranyl diphosphate (GGDP) that forms one-half of all C40 carotenoids. The head-to-head condensation of two GGDP molecules results in the first colorless carotenoid, phytoene. Phytoene synthesis is the first committed step in C40 carotenoid biosynthesis (Britton et al. 1998, Sandmann 2001). 

FIGURE 3.14. Isopentyl diphosphate Isomerase mediates Isomerization of IPP and DMAPP. 

Figure 1. Time dependence of the isomerisation of isopentyl diphosphate and the formation of phytoene in the stroma of daffodil chromoplasts. A at 25 C. B at lO C.

U. tomentosa is a significant traditional medicinal plant that is an important source of monoterpenoid oxindole alkaloids (MOAs) with bioactivities including immunomodulatory, cytotoxic, anti-HIV, and antileukemic activities [100]. It will be of interest to understand biosynthetic insights of bioactive compounds of this plant as an example here. Studies have reported the regulation of biosynthesis of sterols and triterpenes in U. tomentosa [100]. Administration of pectin to U. tomentosa cell suspension cultures increased the activity of isopentyl diphosphate isomerase of ursolic and oleanolic acid. The treated cells also transformed a higher percentage of labeled mevalonic acid precursors into triterpenes and resulted in the decrease in activity of far-nesyl diphosphatase by a factor of two when compared to the control. The... 

Figure 10.7 All terpenes are derived from allylic diphosphates which are polymers of repeating isopentyl units (IPP) put together by the action of prenyltransferases. In plants, IPP can be derived from the mevalonate biosynthetic pathway (a cytoplasmic pathway) or the methyl erythritol phosphate pathway (a plastidic pathway). Monoterpenes are then derived from the CIO precursor geranyl diphosphate (GPP), sesquiterpenes from the C15 precursor famesyl diphosphate (FPP), and diterpenes from the C20 precursor geranylgeranyl diphosphate (GGPP) by the action of terpene synthases or cyclases, which divert carbon into the specific branch pathways.

---