Terpenes biochemical pathways

Nevertheless, the main physiological action reported for limonene concerns cancer prevention and therapy. In fact, there is some evidence to suggest that /(-limonene may afford protection from chemical tumor formation. Limonene has been shown to block and suppress carcinogenic events, because certain biochemical pathways in tumor tissues may be sensitive to the inhibitory action of /(-limonene and certain terpene constituents of essential oils (Elson and Yu, 1994). 

In addition to terpenes, carbohydrates serve as a precursor of furanones in plants. The formation of 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF) is an example. This compound, and various forms thereof, are key to the aroma of strawberry. Several researchers have studied the biochemical pathways responsible for the formation of this compound [34,35]. The pathway presented in Figure 4.10 illustrates DMHF formation from its key precursor, 6-deoxy-D-fructose. 

Of the four major classes of biochemicals (carbohydrates, proteins, nucleic acids and lipids), experiments have shown that the first three classes could have arisen through prebiotic chemistry. Although the biosynthesis of many natural products can be traced back to acetate (e.g. fatty acids, terpenes and polyketide biosynthesis) or amino acids (e.g. alkaloid biosynthesis), there are many whose biosynthetic origins are either obscure or result from a complex combination of pathways (Fig. 2). 

The isoprene pathway produces a diverse range of natural products such as terpenes and steroids. A number of complex biochemical transformations are involved, many of which have been proposed to involve short-lived carbocation intermediates. Two recent studies provide a brief introduction. 

Rama-Devi, J. and Battacharyya, P.K. 1977. Microbial transformation of terpenes Part XXIV. Pathways of degradation of geraniol, nerol and limonene by Pseudomonas incognita (linalool strain). Indian J. Biochem. Biophys. 14 359-363. 

This rapid, usually localized, response also includes biochemical changes, in which monoterpene, diterpene, and sesquiterpene concentrations rise. These terpenes are derived from isoprenoids synthesized via the mevalonate or 1-deoxy-D-xylulose-5-phosphate pathways in the cytosol, endoplasmic reticulum, and plastids. A diverse array of terpenoid synthethases yield the parent compounds, and a number of genes have been characterized. Induction can be elicited by applying methyl jasmonates. ... 

Madyastha, K.M. and P.K. Bhattacharyya, 1968. Microbiological transformation of terpenes. Part XIII. Pathways for degradation of -cymene in a soil pseudomonad (PL-strain). /wrfiaH/. Biochem., 5 161-167. 

Shukla, O.P., and P.K. Bhattacharyya, 1968. Microbiological transformations of terpenes Part XI—Pathways of degradation of a- P pinenes in a soil Pseudomonad (PL-strain). Indian J. Biochem., 5 92-101. Shukla, O.P., M.N. Moholay, and P.K. Bhattacharyya, 1968. Microbiological transformation of terpenes Part X—Fermentation of a- Ppinenes by a soil Pseudomonad (PL-strain). Indian J. Biochem., 5 79-91. Southwell, I.A. and T.M. Flynn, 1980. Metabolism of a- and p-pinene,/)-cymene and 1,8-cineole in the brush tail possum. XenobiotiM, 10 17-23. 

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