Mentha piperita monoterpene biosynthesis

Burbott, A. ]., R. Croteau, W. E. Shine, and W. D. Loomis. Biosynthesis of cyclic monoterpenes by cell freee extracts of Mentha piperita. Int Congr Essent Oils (PAP) 6 Allured Publ Corp Oak Park, 111 1974 17 1. 

Evidence for conjugate reduction as a key step in monot-erpene biosynthesis has been obtained from studies of the oxygenated monoterpenes of Mentha piperita (Fig. 19.10) (Croteau, 1984). The pathway from isopiperitenone to the menthol esters was deduced largely by time-course studies and direct feeding experiments. Other evidence supports the intermediacy of /-limonene (11) as the first cyclization product of GPP in this plant. This is followed by the adlylic oxidation of the olefin and subsequent isomerization and reduction of the double bonds of isopiperitenone to the men-thones (such as 26). Furthermore, stereospecific dehydrogenases responsible for the synthesis of /-menthol (27) and d-neomenthol (28) have been isolated (Croteau, 1984). 

The enzymes responsible for the hydroxylation of monoterpenes such as (— )-limonene (11) from peppermint Mentha piperita), spearmint Mentha spicata), and perilla Per-ilia frutescens) have been isolated and characterized (Karp et al., 1987,1990). Microsomal preparations from the epidermal oil glands of these plants catalyze the NADPH and 02-dependent allylic hydroxylation of (- )-(45)-limonene (the major olefinic constituent of each of the three species) at C-3, C-6, and C-7, respectively, to produce (- )-rra j-isopiper-itenol (34), (- )- m 5-carveol (35), and (- )-perillyl alcohol (36) (Fig. 19.9) (Karp et al., 1990). These transformations are the key steps in the biosynthesis of oxygenated monoterpenes in the respective species. The enzymes appear to be... 

The monoterpene biosynthesis in different species of Lamiaceae, for example, sage (Salvia officinalis) and peppermint (Mentha x piperita), is restricted to a brief period early in leaf development (Croteau et al., 1981 Gershenzon et al., 2000). The monoterpene biosynthesis in peppermint reaches a maximum in 15-day-old leaves, only very low rates were observed in leaves younger than 12 days or older than 20 days. The monoterpene content of the peppermint leaves increased rapidly up to day 21, then leveled off, and kept stable for the remainder of the leaf life (Gershenzon et al., 2000). 

The relationship of cyclic monoterpenes, e.g. 4.3) and 4.53), to geranyl pyrophosphate 4.41) is an obvious one. The tram double bond in 4.41) means that 4.41) cannot cyclize directly to give monoterpenes such as 4.53), and neryl pyrophosphate 4.51) may be more directly involved in biosynthesis. [A cell-free preparation of Mentha piperita has been obtained which will catalyse the conversion of neryl pyrophosphate 4.51) into a-terpineol 4.3) [65].] The conversion of geraniol 4.2) into nerol 4.49) is well known and involves a stereospecific proton removal from C-1 loss of a proton indicates that the aldehyde 4.50) is involved in double-bond isomerization [66]. Initiation of cyclic monoterpene formation can be seen as... 

When we first undertook studies of monoterpene biosynthesis in peppermint (Mentha piperita), we and other plant biochemists were handicapped by inadequate methodology and by inadequate understanding of plants. Gas chromatography was not yet available. It was assvimed that secondary metabolites were synthesized slowly and irreversibly, so tracer experiments were conducted over periods of days instead of minutes or hours. Finally, the unique problems Of plant enzymology were not understood. 

McCASKILL, D., CROTEAU, R., Monoterpene and sesquiterpene biosynthesis in glandular trichomes of peppermint Mentha x piperita) rely exclusively on plastid-derived isopentenyl diphosphate, Planta, 1995,197,49-56. 

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