Dimethylallyl diphosphate DMAPP

Figure 27.9 Mechanism of the coupling reaction of dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP), to give geranyl diphosphate (GPP).

Ginsenosides are bios)mthesized via the isoprenoid pathway in the cytosol with mevalonic acid as the precursor for isopentenyl diphosphate (IFF) and dimethylallyl diphosphate (DMAPP), which are the two C5 starting units in the bios)mthesis of ginsenosides and other terpenoids... 

This dependence on light levels and temperature is believed to be due to the mechanism of production of isoprene in the plant, which involves the enzyme isoprene synthetase and dimethylallyl diphosphate (DMAPP) as a precursor to isoprene (e.g., see Silver and Fall, 1995 and Monson et al., 1995). Either the enzyme, the formation of DMAPP, or both may be light sensitive (Wildermuth and Fall, 1996). The temperature effect has been attributed to effects on the enzyme, increasing its activity initially and then leading to irreversible denaturation (and/or possibly membrane damage) (Fall and Wildermuth, 1998). 

A C5 isoprene unit in the form of dimethylallyl diphosphate (DMAPP) may also act as an... 

One of the more exciting and recent advances in the field of plant biochemistry has been the discovery of the mevalonate-independent pathway for the biosynthesis of isoprenoids (Fig. 10.4). This new pathway, referred to a the methyl-erythritol-phosphate or MEP pathway for the first intermediate committed solely to the biosynthesis of isoprenoids, was first discovered in prokaryotes capable of accumulating hopenes, the equivalent of eukaryotic sterols. 6,17 The MEP pathway has since been confirmed in plants and, not surprisingly, has been localized to chloroplasts.18 Operation of the MEP pathway is intimately related to the reactions of CO2 fixation and photosynthesis, as evidenced by the two immediate precursors pyruvate and phosphoglyceraldehyde for this pathway. Two important features of this pathway are that mevalonate is not an intermediate in the plastidic synthesis of isopentenyl (IPP) and dimethylallyl diphosphate, (DMAPP), and this pathway... 

All isoprenoids are biosynthesized from two isomeric 5-carbon compounds, isopentenyl diphosphate (IPP, 86) and dimethylallyl diphosphate (DMAPP, 87) (Fig. 11). The mammalian pathway for the biosynthesis of these key biosynthetic precursors from three acetyl-CoA units (83) via mevalonate (85) had been elucidated in the 1950s (51). In the wake of that pioneering work, it became established dogma that all terpenoids are invariably of mevalonate origin, even in the face of significant aberrant findings. 

Figure 11 Biosynthesis of isoprenoid type cofactors. 18, Heme a 39, pyridoxal 5 -phosphate 43, 1-deoxy-D-xylulose 5-phosphate 46, thiamine pyrophosphate 83, acetyl-CoA 84, (S)-3-hydroxy-3-methylglutaryl-CoA 85, mevalonate 86, isopentenyl diphosphate (IPP) 87, dimethylallyl diphosphate (DMAPP) 88, pyruvate 89, D-glyceraldehyde 3-phosphate 90, 2C-methyl-D-erythritol 4-phosphate 91, 2C-methyl-erythritol 2,4-cyclodiphosphate 92, 1-hydroxy-2-methyl-2-( )-butenyl 4-diphosphate 93, polyprenyl diphosphate 94, cholecalciferol 95, fS-carotene 96, retinol 97, ubiquinone 98, menaquinone 99, a-tocopherol.

Most terpenoids are derived from mevalonic acid (MVA) through the universal precursor isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP). Thus, the vast majority of terpenoids contain the basic structural residue 2-methylbutane, often less precisely referred to as isoprene units. These C5 hemiterpene units combine with... 

Although terpenoids are extraordinarily diverse, all of them originate through the condensation of the universal five-carbon precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), Fig. (5). 

Isoprenoids are the largest group of known natural products comprising at least 35 000 compounds. Pioneering work in the 1950s resulted in the elucidation of the mevalonate pathway for the biosynthesis of the two universal isoprenoid precursors isopentenyl diphosphate (IPP, 29, Figure 8) and dimethylallyl diphosphate (DMAPP, 28). 

Of the two existing isoprenoid biosynthetic pathways (Fig. 3), DXP is used by most prokaryotes for production of IPP and dimethylallyl diphosphate (DMAPP) [65,66]. With the available knowledge of the genes involved in the DXP pathway, several groups have studied the impact of changed expression levels of these genes on the production of reporter terpenoids. Farmer and liao reconstructed the isoprene biosynthetic pathway in Escherichia coli (E. colt) to produce lycopene, which was used as an indication... 

The early steps in the ergot alkaloid biosynthetic pathway are outlined in Fig. 1. The first determinant and rate-limiting step is the prenylation of tryptophan to 4-(y,y-dimethylallyl)tryptophan (DMAT), catalyzed by dimethy-lallyl-diphosphate L-tryptophan dimethylallyltransferase (DMAT synthase EC 2.5.1.34) (Heinstein et al., 1971 Gebler and Poulter, 1992). The prenyl group for the DMAT synthase reaction is provided in the form of dimethylallyl diphosphate (DMAPP), which is derived from mevalonic acid. After the formation of DMAT, the free amino group of this intermediate is N-methylated with a methyl group donated by S-adenosylmethionine (AdoMet). The N-methylated DMAT is then converted into chanoclavine I by closure of the... 

Isopentenyl diphosphate (IPP) isomerase catalyzes the conversion of IPP to dimethylallyl diphosphate (DMAPP), an early step in isoprenoid metabolism (Equation (25)). 

E. coli and other Gram-negative bacteria synthesize the IPP and dimethylallyl diphosphate (DMAPP) by the mevalonate-independent pathway, also known as the nonmevalonate pathway (other names are deoxyxylulose phosphate or methylerythritol phosphate pathway). In contrast. Gram-positive bacteria and eukaryotes, including yeast, synthesize the side chain precursors by the mevalonate pathway. Interestingly, Streptomycetes possess both the mevalonate and nonmevalonate pathways. These pathways are the subject of Chapters 1.12, 1.13, 1.14, 1.22. 

Fig. 1.4 Outline of terpenoid biosynthesis from isopentenyl diphosphate (IPP) via dimethylallyl diphosphate (DMAPP), gcranyl diphosphate (GPP), famesyl diphosphate (FPP) and geranylgcranyl diphosphate (GGPP). These reactions are catalyzed by isoprenyl diphosphate synthases and terpene synthases. The major products of the monoterpene, sesquiterpene, and diterpene pathways that constitute the oleoresm of Picea abies are listed. The general precursor IPP is derived either from the plastidial methylerythritol phosphate (MEP) pathway or the cytosolic mevalonaic pathway.

Isopentenyl diphosphate (IPP) isomerase (EC 5.3.3.2) catalyses the interconversion of IPP and dimethylallyl diphosphate (DMAPP). During a growth cycle of a suspension culture of C. roseus, relatively highest IPP isomerase activity was found between 4 and 6 days after subculture about 20 pkat/mg protein. By Western blot analysis, using purified polyclonal antibodies raised against IPP isomerase from Capsicum annuum chloroplasts, two isoforms of IPP isomerase were detected in the C. roseus extracts [13]. 

---