Monoterpenes metabolism linalool

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. 

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-... 

Shimizu et al. (72) established that B. cinerea did not produce any monoterpenes in must under culture conditions but led to an oxidation of linalool. Although the authors identified the four linalool oxides among the products, they did not identify the major metabolite, which from their data, was probably dienediol 31. Thus a parasitic organism commonly found on grapes can metabolize one of the major monoterpene flavorants of the fruit to a flavorless polyol. Of note in this regard were the reported losses of both aroma and volatile terpenes in botrytised grapes (73). 

The tremendous diversity of volatile monot-erpenes, sesquiterpenes and diterpenes arises from enzymatic modification of the non-volatile prenyl diphosphate intermediates GPP, FPP and GGPP through the action of terpene synthases (TPS) [57, 58], many of which have the distinctive ability to catalyze the formation of multiple products from a single prenyl diphosphate snb-strate [59-61]. A recently isolated monoterpene synthase from Nicotiana suaveolens flowers was found to produce a blend of 5 cyclic and 2 acyclic monoterpenes, all of which are components of N. suaveolens floral scent [62]. In Arabidopsis, two terpene synthases account for the biosynthesis of nearly all sesquiterpenes found in the floral volatile blend [63]. In addition to sesquiterpenes, Arabidopsis flowers also emit monoterpenes dominated by P-myrcene and (5)-linalool. While P-myrcene could likely be synthesized by multi-product monoterpene synthases [64, 65], one single-product monoterpene synthase may be solely responsible for the emission of (5)-linalool [65]. In snapdragon, two specialized single-product monoterpene synthases are responsible for the biosynthesis of the two floral monoterpenes, myrcene and ( )-P-ocimene [66]. The reaction mechanism of TPSs involves the formation of carbocationic intermediates which can then be differentially metabolized to form multiple products [57, 58]. 

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