Isoprenoid compounds biosynthesis

Subsequent cyclizations, dehydrogenations, oxidations, etc., lead to the individual naturally occurring carotenoids, but little is known about the biochemistry of the many interesting final structural modifications that give rise to the hundreds of diverse natural carotenoids. The carotenoids are isoprenoid compounds and are biosynthesised by a branch of the great isoprenoid pathway from the basic C5-terpenoid precursor, isopentenyl diphosphate (IPP). The entire biosynthesis takes place in the chloroplasts (in green tissues) or chromoplasts (in yellow to red tissues). 

Spurgeon SL, Porter JW (1981) In biosynthesis of isoprenoid compounds. In Porter JW, Spurgeon SL (eds) John Wiley and Sons, New York, p 1... 

Bark beetles primarily utilize isoprenoid derived pheromones [100,101] and have been the most studied regarding their biosynthesis [8,98]. Earlier work indicated that the isoprenoid pheromones could be produced by the beetle altering host derived isoprenoids however more recent work indicates that for the most part bark beetles are producing pheromones de novo. The production of isoprenoids follows a pathway outlined in Fig. 4 which is similar to the isoprenoid pathway as it occurs in cholesterol synthesis in mammals. Insects cannot synthesize cholesterol but can synthesize farnesyl pyrophosphate. Insects apparently do not have the ability to cyclize the longer chain isoprenoid compounds into steroids. The key enzymes in the early steps of the isoprenoid... 

Elimination usually involves loss of a proton together with a nucleophilic group such as -OH, -NH3+, phosphate, or pyrophosphate. However, as in Eq. 13-18, step c, electrophilic groups such as -COO-can replace the proton. Another example is the conversion of mevalonic acid-5-pyrophosphate to isopentenyl pyrophosphate (Eq. 13-19) This is a key reaction in the biosynthesis of isoprenoid compounds such as cholesterol and vitamin A (Chapter 22). The phosphate ester formed in step a is a probable intermediate and the reaction probably involves a carbo-cationic intermediate generated by the loss of phosphate prior to the decarboxylation. 

The second five-carbon branched unit, in which the branch is one carbon further down the chain, is an intermediate in the biosynthesis of polyprenyl (isoprenoid) compounds and steroids. Three two-carbon units are used as the starting material with decarboxylation of one unit. Two acetyl units are first condensed to form acetoacetyl-CoA. Then a third acetyl unit, which has been transferred from acetyl-CoA onto an SH group of the enzyme, is combined with the acetoacetyl-CoA through an ester condensation. The thioester linkage to the enzyme is hydrolyzed to free the product 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This sequence is illustrated in Eq. 17-5. The thioester group of HMG-CoA is reduced to the... 

The terpenes, carotenoids, steroids, and many other compounds arise in a direct way from the prenyl group of isopentenyl diphosphate (Fig. 22-1).16a Biosynthesis of this five-carbon branched unit from mevalonate has been discussed previously (Chapter 17, Fig. 17-19) and is briefly recapitulated in Fig. 22-1. Distinct isoenzymes of 3-hydroxy-3-methylglutaryl-CoA synthase (HMG-CoA synthase) in the liver produce HMG-CoA destined for formation of ketone bodies (Eq. 17-5) or mevalonate.7 8 A similar cytosolic enzyme is active in plants which, collectively, make more than 30,000 different isoprenoid compounds.910 However, many of these are formed by an alternative pathway that does not utilize mevalonate but starts with a thiamin diphosphate-dependent condensation of glyceraldehyde 3-phosphate with pyruvate (Figs. 22-1,22-2). 

Foster, J.M., Pennock, J.F., Marshall, I. and Rees, H.H. (1 993) Biosynthesis of isoprenoid compounds in Schistosoma mansoni. Molecular and Biochemical Parasitology 61, 275-284. 

John W. Porter and Sandra L. Spurgeon, "Biosynthesis of Isoprenoid Compounds" Vol.l. A Wiley-Interscience Publication, John Wiley and Sons., New York, (l98l). 

Porter, J. W., and Spurgeon, S. L. (1981, 1983) Biosynthesis of Isoprenoid Compounds, Vols. 1 and 2. John Wiley Sons, New York. 

Several metabolic pathways for the biosynthesis of aromatic compounds are now known, (a) The aromatization of alicyclic and isoprenoid compounds derived from mevalonic acid, as in the formation of estrone (I) from testosterone (II). A very common example of this process, which has not yet been experimentally demonstrated, is probably the aromatization of a O OH... 

Qureshi N, Porter JW. Conversion of acetyl-coenzyme A to isopentenyl pyrophosphate. In Biosynthesis of isoprenoid Compounds. J. W. Porter and S. L. Spurgeon, eds. 1981. John Wiley, New York. pp. 47-94. 

This paper describes the structural analysis of naturally occurring ois-1,4 polyisoprenes using 13C NMR spectroscopy. First, the structural characterization of polyprenols, which are linear isoprenoid compounds containing 30 to 100 carbons, was carried out on the basis of information obtained from acyclic terpenes having various ois and trans isoprene units as model compounds. This method was also applied to the structural analysis of polyisoprenes. The elucidation of the structure of the end groups and the arrangement of isoprene units provides information on the mechanism of the biosynthesis of polyprenyl compounds in nature. 

The biosynthesis of sterols takes place via the protracted sterol/isoprenoid biosynthetic pathway (Chapter 1). Although the major portion of the carbon flux through this pathway is normally directed into sterols, several branches exist leading to the production of other isoprenoid compounds needed by the cell, such as ubiquinone, dolichol and isopentenyl adenine. Total carbon flux is regulated through the enzymes of the early, or common, portion of the pathway of which the most important is HMG-CoA reductase. Distribution of carbon between the various end products is regulated at later stages of the pathway. 

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