Biosynthetic enzymes terpenoids

Independent synthesis of the identified terpenoid is often required to confirm structural assignment (51) and to test the biological and/or pharmacological functions. In addition, biosynthetic studies often require the synthesis of putative precursors for functional characterization of enzymes. Terpenoid stractures challenge chemists in many of the same ways that other natural products do. Their structural diversity (complicated by stereochemistry, carbocyclic skeletons, and often multiple functionalization) provides opportunities for synthetic organic chemists to develop new methodologies for synthesis. Recently, Mai-mone and Baran (52) have reviewed some synthetic challenges terpenoids present and the solutions employed. 

Terpenoid indole alkaloid biosynthetic enzymes are associated with at least three different cell types in C. roseus TDC and STR are localized to the epidermis of aerial organs and the apical meristem of roots, D4H and DAT are restricted to the laticifers and idio-blasts of leaves and stems, and GlOH is found in internal parenchyma of aerial organs (St-Pierre et al. 1999 Buriat et al. 2004) thus, vindoline pathway intermediates must be translocated between cell types. Moreover, enzymes involved in terpenoid indole alkaloid biosynthesis in C. roseus are also localized to at least five subcellular compartments TDC, D4H and DAT are in the cytosol, STR and the peroxidase that couples catharanthine to vinblastine are localized to the vacuole indicating transport of tryptamine across the tono-plast, SGD is a soluble enzyme associated with the cytoplasmic face of the endoplasmic reticulum, the P450-dependent monooxygenases are integral endomembrane proteins, and the N-methyltransferase involved in vindoline biosynthesis is localized to thylakoid membranes (De Luca and St-Pierre 2000). 

Geerlings A, Martinez-Lozano Ibanez M, Memelink J, van der Heijden R, Verpoorte R (2000) The strictosidine 6-D-glucosidase gene from Catharanthus roseus is regulated coordinately with other terpenoid-indole alkaloid biosynthetic genes and the encoded enzyme is located in the endoplasmic reticulum. J Biol Chem 275 3051-3056... 

New enzymes for drug discovery have been identified through biosynthetic studies on microbial metabolites. It has been long accepted that isopentenyl diphosphate, an intermediate of sterols and terpenoids, is synthesized only through... 

Figure 7.3 Biosynthetic pathway for terpenoid indole alkaloids showing the location of enzymes for which the corresponding cDNAs have been isolated.

The results from kinetic studies of MVK in Methanococcus jannaschii, showed that the Arg 196 is an essential residue for the function of this enzyme and the Lys 272-Glu 14 plays an important role in maintaining the active site microenvironment that is essential for the catalytic activity of this enzyme [285]. These results suggest that MVK has a regulating role in the terpenoid biosynthetic pathway, as well as in several growth and development processes in plants. 

In D. punctata, JH III is biosynthesized in retrocerebral endocrine organs, the corpora allata (CA) [45]. The sesquiterpenoid skeleton of this compound is formed through the terpenoid biosynthetic pathway from acetyl-CoA. The early steps of this pathway involve the sequential condensation of three acetyl-CoA molecules (3 x 2C) to form the biosynthetic intermediate mevalonate (MVA, 6C). 3-Hydroxy-3-methylglutaryl CoA reductase, which catalyzes the formation of MVA, is thought to be the rate-limiting enzyme in this pathway [59], although the... 

HMG-CoA reductase is the most important regulatory enzyme for the cholesterol biosynthetic pathway and other isoprenoids/terpenoids. HMG-CoA reductase catalyzes the reaction that follows ... 

Sesquiterpenes (sesquiterpenoids). A structurally highly diverse class of terpenoids with 15 carbon atoms skeleton derived biosynthetically from famesyl pyrophosphate (FPP) ( famesol, isoprene rule, ter-penes). More than 70 different ring systems are formed by enzyme-catalyzed cyclization of the linear parent structure these cyclic structures can be further modified by 1,2- and 1,3-hydride shifts, renewed cycliza-tions, hydroxylations, and other subsequent reactions. S. are widely distributed in plants, fiingi, and animals but are less common in bacteria. Specific biosynthetic routes are often characteristic for certain organisms. Thus, basidiomycetes preferentially use humulene as the basis for the syntheses of protoilludanes, illu-danes, lactaranes, hirsutanes, and related S. skeletons. Individual S. systems are also known for liverworts and marine organisms. In addition, liverworts often contain the optical antipodes of S. known from plants. 

One of the best understood biosynthetic pathways for terpenoids is the biosynthesis for menthol in mint plants. All the enzymes are identified, cloned, and characterized [43]. Menthol plays an important role as aroma in food, cigarettes, and medications for the pulmonary tract and in cosmetics. Improvements of yield or... 

The stereochemistry is well established, and many questions concerning the overall mechanism of the condensation have now been resolved. Famesyl pyrophosphate synthetase (EC 2.5.1.1) is the key enzyme in the biosynthetic pathways for several classes of terpenes. This enzyme catalyzes l -4 condensation between IPP and DMAPP, or geranyl pyrophosphate, polymerizations that constitute the major building steps of terpenoid biosynthesis (Fig. 21.2) (Poulter and Rilling, 1978 Poulter et al., 1978, 1981). The condensation... 

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