Isoprenoids sources

The antimicrobial action of ethambutol, like that of isoniazid, is specific for mycobacteria, suggesting a target in the unique components of the mycobacterial cell wall. Cells treated with ethambutol accumulate an isoprenoid intermediate, decaprenyl-arabinose which is the source ofarabinose in the arabinogalactan polymer. This suggests that ethambutol blocks assembly of the arabinogalactan through inhibition of an arabinosyl transferase enzyme. 

More than 600 different carotenoids from natural sources have been isolated and characterized. Physical properties and natural functions and actions of carotenoids are determined by their chemical properties, and these properties are defined by their molecular structures. Carotenoids consist of 40 carbon atoms (tetraterpenes) with conjugated double bonds. They consist of eight isoprenoid units j oined in such a manner that the arrangement of isoprenoid units is reversed at the center of the molecule so that the two central methyl groups are in a 1,6-position and the remaining nonterminal methyl groups are in a 1,5-position relationship. They can be acyclic or cyclic (mono- or bi-, alicyclic or aryl). Whereas green leaves contain unesterified hydroxy carotenoids, most carotenoids in ripe fruit are esterified with fatty acids. However, those of a few... 

The peppermint oil gland secretory cell cDNA library has proven to provide a highly enriched source of candidate genes involved in essential oil biosynthesis. A functional genomics approach has successfully been employed to clone genes involved in the mevalonate-independent pathway of isoprenoid biosynthesis and in the peppermint-specific steps producing (-)-menthol and (-)-menthone. The optimization of LC-MS technology to profile phosphoiylated carbohydrates and... 

Terpenes are a large and diverse class of compounds produced by a wide variety of organisms, though plants are an especially prolific source. The terms terpenoid and isoprenoid can be used interchangeably with terpene, though, strictly, terpenes are hydrocarbons (composed only of carbon and hydrogen) while terpenoids and iso-prenoids have been further functionalized. 

Cvejic JH, Rohmer M (2000) C02 as main carbon source for isoprenoid biosynthesis via the mevalonate-independent methylerythritol 4-phosphate route in the marine diatoms Phaeodactylum tricomutum and Nitzschia ovalis. Phytochemistry 53 21-28 de Nys R, Steinberg PD, Willemsen P, Dworjanyn SA, Gabelish CL, King RJ (1995) Broad-spectrum effects of secondary metabolites from the red alga Delisea pulchra in antifouling assays. Biofouling 8 259-271... 

The pathway also operates in some bacteria and apparently is the sole source of isoprenoid compounds for the unicellular alga Scenedesmus.28 The pathway is outlined in Fig. 22-2. Pyruvate is decarboxylated by a thiamin diphosphate-dependent enzyme,29 and the resulting enamine is condensed with D-glyceraldehyde 3-phosphate to form 1-deoxyxylulose 5-phosphate.28, i0 31a The latter undergoes an isomeroreductase rearrange-... 

The pioneering work of Evans, Emerson and Emerson led to the isolation of a-tocopherol, a phenol exhibiting vitamin-E-like activity in biological systems. Now, eight compounds, usually oils, have been identified from plant sources, with similar vitamin-E-like actions. The tocopherols differ only in the number of methyl groups in the aromatic ring and therefore can be regarded as derivatives of 2-methyl-6-chromanol, onto which a 16-carbon isoprenoid chain is attached at C-2 and which is methylated at positions C-5, C-7 and C-8, respectively. 

Branched and cyclic hydrocarbons have also been used as paleomarkers, principally in lake sediments, to interpret past changes in organic matter sources. In particular, isoprenoid hydrocarbons such as pristane (C19 isoprenoid hydrocarbon) and phytane (C20 isoprenoid hydrocarbon) (both derived from phytol) have been used as indicators of herbivorous grazing and methanogenesis, respectively. 

Statins. Statins, such as atorvastatin (Lipotor), simvastatin (Zocor) and lovastatin (Mevacor), are fungal-derived HMG-CoA reductase inhibitors. Treatment results in an increased cellular uptake of LDLs, since the intracellular synthesis of cholesterol is inhibited and cells are therefore dependent on extracellular sources of cholesterol. However, since mevalonate (the product of the HMG-CoA reductase reaction) is also required for the synthesis of other important isoprenoid compounds besides cholesterol, long-term treatments carry some risk of toxicity. 

The IBP (Figure 12.1) is the source of over 23,000 naturally occurring isoprenoids [1]. The first chemical studies of isoprenoids were begun in the early 1800s (Figure 12.2). Between 1800 and 1884, a large number of compounds with the empirical formula of CsHg were isolated. Otto Wal-lach, in a series of papers published between 1884 and 1887, was the first to... 

Ulmoprenol (3) is an interesting new hexaprenoid from Eucommia ulmoides. A series of head-to-head linked isoprenoid hydrocarbons has been isolated from petroleum sources. ... 

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