Plant isoprenoids

Bouvier, R, Rahier, A., and Camara, B., Biogenesis, molecular regulation and function of plant isoprenoids, Progr. Lipid Res. 44, 357, 2005. 

FRASER, P.D., ELISABETE, M., PINTO, S., HOLLOWAY, D.E., BRAMLEY, P.M., Application of high-performance liquid chromatography with photodiode array detection to the metabolic profiling of plant isoprenoids, Plant J., 2000, 24, 551-558. 

ZEIDLER, J., SCHWENDER, J., MULLER, C WIESNER, J., WEIDEMEYER, C., BECK, E., JOMAA, H., LICHTENTHALER, H.K., Inhibition of the non-mevalonate 1-deoxy-D-xylulose 5-phosphate pathway of plant isoprenoid biosynthesis by fosmidomycin, Z. Naturforsch., 1998,53c, 980-986. 

Liu Y, Wang H, Ye H-C, Li G-F. (2005) Advances in the plant isoprenoid biosynthesis pathway and its metabolic engineering. J Integr Plant Biol 47 769-782. 

The separation of plant isoprenoid lipids, including ubiquinone, phylloquinone [=MK-4(II,III,IV-H6], and plastoquinone (160) by h.p.l.c. has been described. 

SCHEME 1.—The Biosynthesis and Metabolism of Dolichyl Phosphate and Other Plant Isoprenoids. 

A far more complex situation arises in higher plants that use both the pathways in parallel.53 With hindsight, it is even obvious that the belated discovery of the deoxyxylulose pathway can be traced to a significant extent to the very occurrence of both the pathways in plants. More specifically, due to metabolite exchange between the two pathways that is the subject of this chapter, it appears likely that labeled mevalonate can contribute at least some label to most if not all plant isoprenoids hence, it was easy to jump to the conclusion — fallacious as we now know — that all plant isoprenoids are invariably biosynthesized from mevalonate. 

Relatively little is known about plant sterols. (Most of the research effort in steroid metabolism has been expended in the investigation of steroid-related human diseases.) It appears, however, that the initial phase of plant sterol synthesis is very similar to that of cholesterol synthesis with the following exception. In plants and algae the cyclization of squalene-2,3-epoxide leads to the synthesis of cycloartenol (Figure 12.30) instead of lanosterol. Many subsequent reactions in plant sterol pathways involve SAM-mediated methylation reactions. There appear to be two separate isoprenoid biosynthetic pathways in plant cells the ER/cyto-plasm pathway and a separate chloroplast pathway. The roles of these pathways in plant isoprenoid metabolism are still unclear. 

Despite the popularity of in vitro experimentation concerning the cellular mechanisms of carcinogenic prevention by essential oil components (mainly by inducing apoptosis), there is no evidence that the direct administration of essential oils can cure cancer. There is evidence to suggest that the mevalonate pathway of cancer cells is sensitive to the inhibitory actions of dietary plant isoprenoids (e.g., Elson and Yu, 1994 Duncan et al., 2005). Animal testing has shown that some components can cause a signi cant reduction in the incidence of chemically induced cancers when administered before and during induction (e.g., Reddy et al., 1997 Uedo et al., 1999). 

Bouvier F, Rahier A, Camara B (2005) Biogenesis, molecular recognition and function of plant isoprenoids. Prog Lipid Res 44 357-429... 

Kirby J, Keasling JD (2009) Biosynthesis of plant isoprenoids perspectives for microbial engineering. Annu Rev Plant Biol 60 334—355... 

Branched-chain amino acids as precursurs of plant isoprenoids L-Leucine and L-valine, when fed to germinating pea seeds (Pisum sativum) were incorporated into squalene and 6-amyrin [39]. Chemical degradation by ozonolysis of the radioactive squalene revealed an equal distribution of the radioactivity in the IPP-derived (4 portions per molecule) and the DMAPP-derived moieties (2 portions per molecule). However, an unbalanced distribution in favor of the DMAPP-derived moiety of monoterpenoids was found after feeding radioisotopically labeled L-leucine, L-valine, DL-alanine, acetate, and R,S-MVA to intact plants of Cinnamomum camphora and of Pelargonium roseum [40]. The relatively low incorporation of amino acids was explained by several hypotheses a) the radioactivity of amino acids is scattered into other metabolites rather than monoterpenoids b) there is a great pool of the amino acids which leads to dilution of radioactivity, and c) the low permeation of the amino acids into the biosynthetic site of monoterpenoids [40]. The DMAPP-derived moiety of monoterpenoids, biosynthesized from [U- C]leucine and [U- ]valine was labeled with more than 64% of the incorporated tracers, while this moiety when derived from [2- " C]MVA contained less than 32% of the tracers [40]. This lends support to the interpretation that both amino acids are incorporated not via MV A, but by an alternate route, e,g, a combination of the well known mammalian leucine degradation pathway and a reversal of the MVA shunt (see below). The distribution pattern in monoterpenoids after administration of [2- ]alanine was similar to that after incorporation of MVA, which indicates that alanine is first metabolized to acetyl-CoA, which then constructs preferentially the IPP-derived moiety of the monoterpenoids via MVA [40]. 

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