Monoterpenes metabolism

In plant plastids, GGPP is formed from products of glycolysis and is eight enzymatic steps away from central glucose metabolism. The MEP pathway (reviewed in recent literature - ) operates in plastids in plants and is a preferred source (non-mevalonate) of phosphate-activated prenyl units (IPPs) for plastid iso-prenoid accumulation, such as the phytol tail of chlorophyll, the backbones of carotenoids, and the cores of monoterpenes such as menthol, hnalool, and iridoids, diterpenes such as taxadiene, and the side chains of bioactive prenylated terpenophe-nolics such as humulone, lupulone, and xanthohumol. The mevalonic pathway to IPP that operates in the cytoplasm is the source of the carbon chains in isoprenes such as the polyisoprene, rubber, and the sesquiterpenes such as caryophyllene. 

Trudgill PW (1994) Microbial metabolism and transformation of selected monoterpenes. In Biochemistry of Microbial Degradation (Ed C Ratledge), pp. 33-61. Kluwer Academic Publishers, Dordrecht, The Netherlands. 

It is well established that the iridoids are derived from two units of mevalonic acid (97), which itself is derived from acetyl-CoA. Mevalonate is also known to be a metabolic product of leucine (172), and the latter is a precursor of the monoterpene linalool (173). Wigfield and Wen (174) pursued the incorporation of leucine into the monoterpene unit in both vindoline (3) and catharanthine (4), where levels of 0.07 and 0.02%, respectively, were found, irrespective of the amount of precursor fed. This was important because, although initial results were obtained with [2- C] leucine, the specificity of incorporation was determined with 2- C-la-beled precursor. Two carbons in vindoline (3), C-8 and C-24, were en-... 

Isoprene metabolism in plants is very complex. Plants can synthesize many types of aromatic substances and volatile oils from isoprenoids. Examples include menthol (1= 2 ), camphor (1 = 2), and citronellal (1 = 2). These Cio compounds are also called monoterpenes. Similarly, compounds consisting of three isoprene units (1 = 3) are termed sesquiterpenes, and the steroids (1 = 6) are called triterpenes. 

Croteau R, Venkatachalam KV, Metabolism of monoterpenes Demonstration that (-l-)- t-isopulegone, not piperitenone, is the key intermediate in the conversion of (—)- isopiperitenone to (-l-)-pulegone in peppermint Mentha piperita), Arch Biochem Biophys 249 306—315, 1986. 

Nelson SD, McClanahan RH, Knebel N, Xhomassen D, Gordon WP, Doshi S, Xhe metabolism of (A)-(+)-pulegone, a toxic monoterpene, in Petrosky RJ, McCormick SP (eds.), Secondary-Metabolite Biosynthesis and Metabolism, Plenum Press, New York, USA, 1992. 

Overall, however, the immensity of temperate land corresponds to a most various secondary metabolic production, different from that of tropical land. The most renowned alkaloids belong to the morphine class (Chart 6.2.A1), and, in combination with isoprenoids, to the ergot and triterpene classes (Chart 6.2. A2). Prominent in the peptides are the cyclosporins (the first of which was isolated from a fiingus collected in Norway), streptogramins, and P-lactams (Chart 6.2.P). The isoprenoids are represented by pyrethrin monoterpenes, cedrane sesquiterpenes, ginkgolide and taxane diterpenes, ophiobolane sesterterpenes, and arborane and amyrin-like triterpenes (Chart 6.2.1). In the polyketides, epothilones, recently discovered from Myxobacteria, and the long known rapamycin, are two prominent classes of macrolides (Chart 6.2.FA/PO/C). 

Metabolic transformations are characterized by high speed and yield, as well as high regio-, diastereo-and enantio-specificity. Errors in the stereochemistry of the molecules that serve to construct the genetic material are smaller than for the planetary motions. With secondary metabolites, however, enantiomerically inq)ure con unds are also encoimtered, typkally with monoterpenes and alkaloids from terrestrial plants even ant dal pathways in the same organism have been found, albeit as rare events (Guella 1998). 

Eichinger D, Bacher A, Zenk MH, Eisenreich, W. Analysis of metabolic pathways via quantitahve prediction of isotope labeling patterns a retrobiosynthehc 13C NMR study on the monoterpene loganin. Phytochemistry 1999 51 223-236. 

The cases where terpene metabolism has been studied In Insects are very few Indeed. Certain Ips and Dendroctonus bark beetles convert monoterpenes such as a-plnene, 6-plnene and myr-cene to oxidation products, some of which have pheromonal activities ( 5, 3A, 35). A Dendroc tonus bark beetle s cytochrome... 

EOs and their monoterpenes alfected bone metabolism when added to the food of rats. It was demonstrated that these lipophilic compounds inhibited bone resorption [388], It was reported that (2 ,6iI)-8-hydroxy-2,6-dimethyl-2-octenoic acid, a novel monoterpene, from Cistanche salsa had antiosteoporotic properties [389]. 

Pine EOs prevented bone loss in an osteoporosis model (ovariectomized rats). The monoterpenes borneol, thymol and camphor directly inhibited osteoclast resorption [388]. It was observed that inactive monoterpenes can be metabolized to their active forms in vivo thus, ds-verbenol, a metabolite of a-pinene, inhibited osteoclastic resorption activity, in contrast to the parent compound a-pinene. 

Gershenzon, J. and Croteau, R. (1993). Terpenoid biosynthesis the basic pathway and formation of monoterpenes, sesquiterpenes and diterpenes. In Lipid Metabolism in Plants, ed. T. S. Moore Jr, pp. 339-388. Boca Raton, FL CRC Press. 

As mentioned before, a Pseudomonas incognita was isolated by enrichment technique on the monoterpene alcohol linalool that was also able to grow on geraniol, nerol and limonene [36]. The metabolism of limonene by this bacterium was also investigated [37]. After fermentation the medium yielded as main product a crystallic acid, perillic acid, together with unmetabolised limonene, and some oxygenated compounds dihydrocarvone, carvone, carveol, p-menth-8-en-1 -ol-2-one, p-menth-8-ene-1,2-diol or p-menth-1 -ene-6,9-diol (structure not fully elucidated) and finally / -isopropenyl pimelic acid. 

Polzin JJ, Rorrer GL, Cheney DP (2003) Metabolic Flux Analysis of Halogenated Monoterpene Biosynthesis in Microplantlets of the Macrophytic Red Alga Ochtodes secundiramea. Biomol Eng 20 205... 

Croteau R (1991) Metabolism of monoterpenes in mint (Mentha) species. Planta Med 57, S10-S14. 

Pierce H. D., Jr, Conn J. E., Oehlschlager A. C. and Borden J. H. (1987). Monoterpene metabolism in female mountain pine beetles, Dendroctonus ponderosae Hopkins, attacking ponderosa pine. J. Chem. Ecol. 13, 1455-1480. 

The metabolism of 7-endo-fenchol to ci-fenchone in fennel has been studied in quite some detail by Croteau and co-workers (Croteau and Felton, 1980). Croteau et al. (1980a) later reported a soluble enzyme preparation from the leaves of fennel which catalysed the cation-dependent cyclization of both geranyl pyrophosphate and neryl pyrophosphate to the bicyclic rearranged monoterpene 1-enc/o-fenchol. Croteau et al. (1980b) found that (+)-(lS)-fenchone, an irregular bicyclic monoterpene ketone thought to be derived... 

Ringer, K., Davis, E. and Croteau, R. (2005) Monoterpene metabolism. Cloning, expression, and characterization of (—)—isopiperitenol/(—)carveol dehydrogenase of peppermint and spearmint. Plant Physiol, 137, 863-72. 

To date over 30 plant terpenoid synthases have been cloned as cDNAs, and many of these were found to encode enzymes of secondary metabolism (43). Isolation and analysis of six genomic clones encoding monoterpene ((—)-pinene and (—)-limonene), sesquiterpene ((E)-a-bisabolene and S-selinene) and diterpene (abietadiene) synthases from Abies grandis, and a diterpene (taxadiene) synthase from Taxus brevifolia have been reported (44). Overexpression of a cotton farnesyl diphosphate synthase (EPPS) in transgenic Artemesia annua has resulted in 3- to 4-fold increase in the yield of the sesquiterpenoid anti-malarial drug, artemisinin, in hairy roots (45). 

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