And triterpene biosynthesis

GlycoUpids, Synthesis of Imaging Techniqnes Lipids Labeling Techniqnes Lipids Lipidomics Lipids, Semi-synthetic Steroid and Triterpene Biosynthesis PHYSICAL PROPERTIES PHASE BEHAVIOR AND PHASE TRANSITIONS... 

Steroid and Triterpene Biosynthesis Terpenes, Biosynthesis of Terpenoids in Plants ... 

Terpenoids, which are also known as isoprenoids, constitute the most abundant and structurally diverse group of plant secondary metabolites, consisting of more than 40,000 different chemical structures. The isoprenoid biosynthetic pathway generates both primary and secondary metabolites that are of great importance to plant growth and survival. Among the primary metabolites produced by this pathway are phytohormones, such as gibberellic acid (GA), abscisic acid (ABA), and cytokinins the carotenoids, such as chlorophylls and plastoquinones involved in photosynthesis the ubiquinones required for respiration and the sterols that influence membrane stmcture (see also Steroid and Triterpene Biosynthesis) (Fig. 1). Monoterpenoids (CIO), sesquiterpenoids (Cl5), diterpenoids (C20), and... 

Chemistry of Cytochrome P450 Monooxygenases, Glycosyl Transferases and Methyl Transferases Metabolic Engineering Steroid and Triterpene Biosynthesis Terpenoid Biosynthesis... 

Sterols include 4a-methylsterols, intermediates of sterols and triterpens biosynthesis. Analysis of the sterol fraction demostrated the constant presence of P-sitosterol, campesterol and stigmasterol, A -avenasterol, while A" -avenasterol may be absent or present in very low amount. P-sitosterol makes up the 75-90% of the total sterol fraction, the rest of sterols occur in minute quantities. 

Lee MH et al (2004) Enhanced triterpene and phytosterol biosynthesis in Panax ginseng overexpressing squalene synthase gene. Plant CeU Physiol 45 976... 

It is now firmly established that green plants use both iso-prenoid biosynthesis pathways (52). More specifically, sterols and triterpenes are generated in the cytoplasm via the mevalonate pathway, whereas monoterpenes and diterpenes are... 

Terpenoids are derived from the cytosolic mevalonate pathway or from the plastidial 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway (see also Terpenoid Biosynthesis). Both pathways lead to the formation of the C5 units isopentenyl diphosphate and its allylic isomer dimethylallyl diphosphate, which are the basic terpenoid biosynthesis building blocks (Fig. 1). Although increasing evidence suggests that exchange of intermediates occurs between these compartments, the cytoplasmic mevalonate pathway is generally considered to supply the precursors for the production of sesquiterpenes and triterpenes (including sterols) and to provide precursors for protein prenylation and for ubiquinone and heme-A production in mitochondria. In the plastids, the MEP pathway supplies the precursors for the production of isoprene, monoterpenes, diterpenes (e.g., GAs), and tetraterpenes (e.g., carotenoids). 

In the second step of phytoene formation, inorganic pyrophosphate is expelled and a proton is eliminated. Pyridine nucleotide cofactors are not involved, as is the case in triterpene biosynthesis (Fig. 26.3) (Poulter, 1990). 

The biosynthesis of cyclic sesquiterpenes probably includes the formation of enzyme-bound intermediates (Figs. 107 and 108). It is accompanied by the shift of double bonds, hydride ions, etc. The diversity of chemical structures of sesquiterpenes is greater than that of mono-, di-, and triterpenes due to the many different types of cyclizations occuring in this group of secondary products. 

As artemisinin has a terpenic structure, its biosynthesis starts in the formation of isopentenyl diphosphate GPP)> as in all the natural terpenoids. In plants, IPP is synthesized either via the mevalonate pathway in the cytosol or via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway in the plastid. The IPP derived from the mevalonate pathway is generally used in the biosynthesis of sesquiterpenes (such as artemisinin), phytosterols, and triterpenes, and the IPP derived from the non-mevalonate pathway is employed in the biosynthesis of monoterpenes, diterpenes, and tetraterpenes (Fig. 89.15). 

The importance of terpenoids to life is highlighted by the fact that two separate pathways have been found to produce the terpenoid precursor C5 units isopentenyl diphosphate (IDP) and dimethylaUyl diphosphate (DMADP). The mevalonic acid (MVA) pathway is functional in archae, animals and fungi, 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway is found in green algae, and terpenoids are produced by both pathways in bacteria and plants [2]. In plants the MVA pathway is active in the cytosol and it provides C5 units for sesquiterpene, triterpene and polyterpene biosynthesis whereas the MEP pathway occurs in plastids and produces C5 units for isoprene, monoterpenes, diterpenes and carotenoids [1]. Recent reports have indicated metabolic crosstalk between biosynthesis pathways and e.g., the homoterpene DMNT may originate from both pathways. 

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])...

Croteau and Ronald (1983) and Coscia (1984) reviewed chromatographic studies on terpinoids. Those authors considered terpinoids as ubiquitous, structurally diverse, lipophilic compounds. Terpinoids exist in various polymeric forms of the unsaturated branch-chain pentane, isoprenol. Terpenes are characterized as hemi-prenes (C5), monoterpenes (Cio), sesquiterpenes (C15). diterpenes (C20), and triterpenes (Cjo)- A representative hemiprene (hemiterpene) is mevalonic acid, a precursor in the biosynthesis of isoprenoids. Monoterpenes contain numerous... 

Goijman SG, TUrrens JF, Marini-Bettolo GB, Stoppani AOM 1985 Effect of tingenone, a quinonoid triterpene, on growth and macromolecule biosynthesis in Trypanosoma cruzL Ex-perientia 4 646-648... 

In recent years, a range of cytochrome P450 enzymes involved in cyclic terpene hydroxyla-tion has been characterized at the molecular level. These include monoterpene hydroxylases involved in the biosynthesis of essential oils in commercial mint [52], a sesquiterpene hydroxylase performing successive hydroxylations of 5-epi-aristolochene in the biosynthesis of the tobacco phytoalexin capsidiol [53], diterpene hydroxylases involved in the formation of taxol [54, 55], and triterpene hydroxylases involved in the biosynthesis of saponins [56] and brassi-nosteroids [57]. 

Ebizuka, Y., Katsube, Y, Tsutsumi, T., Kushiro, T., and Shibuya, M. 2003. Functional genomics approach to the study of triterpene biosynthesis. Pure Appl Chem 75 369-374. 

Lodeiro, S., Xiong, Q., Wilson, W.K, Kolesnikova, M.D., Onak, C.S., and Matsuda, S.P.T. 2007. An oxidosqualene cyclase makes numerous products by diverse mechanisms A challenge to prevailing concepts of triterpene biosynthesis. J Am Chem Soc 129 11213-11222. 

Dean, P. D. G. (1973). The cyclases of triterpene and sterol biosynthesis. Steroidologia (in press). 

DEVELOPMENTAL REGULATION OF STEROL AND PENTACYCLIC TRITERPENE BIOSYNTHESIS AND COMPOSITION A CORRELATION WITH SORGHUM FLORAL INITIATION... 

M. A. Hartmann and P. Benvenlste, Effects of ageing on sterol metabolism in potato tuber slices. Phytochemistry, 13 2667 (1974) A.M. Atallah, R.T. Axel, R.B. Ramsey and H.J. Nicholas, Biosynthesis of sterols and triterpenes in Pelargonium hortorum. Phytochemistry 14 1529 (1975)... 

This pathway is mainly involved in the biosynthesis of different types of ter-penes (e.g., 16p-aceteoxyhopane-6a-22-diol (42) and zeorin (43)). However, only a few di- and triterpenes are reported from different species of lichens [1]. The pathway is described in Schemes 3 and 4. 

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