Lycopene carotenoid biosynthesis

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

The carotenoid pathway may also be regulated by feedback inhibition from the end products. Inhibition of lycopene cyclisation in leaves of tomato causes increase in the expression of Pds and Psy-1 (Giuliano et al, 1993 Corona et al, 1996). This hypothesis is supported by other studies using carotenoid biosynthesis inhibitors where treated photosynthetic tissues accumulated higher concentrations of carotenoids than untreated tissues (reviewed by Bramley, 1993). The mechanism of this regulation is unknown. A contrary view, however, comes from studies on the phytoene-accumulating immutans mutant of Arabidopsis, where there is no feedback inhibition of phytoene desaturase gene expression (Wetzel and Rodermel, 1998). 

RONEN G, COHEN M, ZAMIR D and HIRSCHBERG J (1999) Regnlation of carotenoid biosynthesis during tomato fruit development expression of the gene for lycopene epsilon cyclase is down regulated during ripening and is elevated in the mutant delta . Plant J, 17, 341-51. 

Desaturation and Isomerization to Coeored Carotenoids Biosynthesis of Lycopene... 

Biosynthesis and Metabolism.—Pathways and Reactions. Two reviews of carotenoid biosynthesis discuss, respectively, the early steps and the later reactions." The former paper deals with the mechanism of formation of phytoene and the series of desaturation reactions by which phytoene is converted into lycopene, and also describes in detail the biosynthesis of bacterial C30 carotenoids. The second paper" presents details of the mechanism and stereochemistry of cyclization and the other reactions that involve the carotenoid C-1 —C-2 double bond and the later modifications, especially the introduction of oxygen functions. 

Besides the engineering of S. cerevisiae for organic acid production, through metabolic engineering it is possible to reconstruct entire pathways. In 1994, Yamano et al. [163] reported the reconstruction of a complete secondary metabolic pathway in S. cerevisiae, resulting in the ability of the yeast to produce p-carotene and lycopene. Carotenoids are a class of pigments used in the food industry and, due to their antioxidant properties, they have wide commercial interest. The biosynthesis of these compounds does naturally not occur in S. cerevisiae and to allow... 

FIGURE 4.4 Scheme for the stepwise desaturation of phytoene to lycopene in carotenoid biosynthesis. (Goodwin, 1980. With permission.)... 

Some details of the stereochemistry of carotenoid cyclization have been elucidated. In the C40 series labelling with stable isotopes (deuterium) has been used for the first time in studies of carotenoid biosynthesis. A Flavobacterium species in the presence of nicotine accumulated the acyclic precursor lycopene (175). When the cells were washed free from the inhibitor and suspended in H20 cyclization of the lycopene proceeded, initiated by High-resolution n.m.r. 

Fig. 5.3 Carotenoid biosynthesis in maize endosperm. Compounds IPP, isopentenyl pyrophosphate FPP, famesyl pyrophosphate GGPP, geranylgeranyl pyrophosphate DMAPP, dimethallyl pyrophosphate. Carotenoid biosynthetic pathway enzymes PSY, phytoene synthase PDS, phytoene desaturase ZDS, zetacarotene desaturase ISO, carotene isomerase LCY-B, lycopene beta cyclase LCY-E, lycopene epsilon cyclase HYD-B, beta-carotene hydroxylase HYD-E, alpha-carotene hydroxylase Isonrenoid biosynthetic pathway enzymes IPPI (IPP isomerase) GGPPS (GGPP synthase). Structures are not representative of the geometrical isomer substrates (e.g. Z-phytoene is a bent structure).

Apel, W., and Bock, R. (2009) Enhancement of carotenoid biosynthesis in transplastomic tomatoes by induced lycopene-to-provitamin A conversion. Plant Physiol, 151, 59-66. 

Illumination in the presence of nicotine diich inhibits the cyclization-step in carotenoid biosynthesis causes a decrease in precursors (peaks a-f), but no xanthoj ylls and carotenes were formed (Fig. 1). An additional pigment (a ) could be detected in these cells ch was identified to be trans-lycopene. 

Temperature effects on carotenoid biosynthesis have been observed with F. aquaeductuum and N. crassa. Quantitative effects are observed in Phy-comyces and the yeasts Rhodotorula rubra and R. penaus. Qualitative changes have been observed in Rhodotorula glutinis. In ripening tomatoes, the synthesis of lycopene, but not /3-carotene, is inhibited in firuit held above 30°C (Goodwin and Jamikom, 1952 Tomes et al., 1956 Czygan and Wil-luhn, 1%7). However, the amount of /3-carotene formed in these fruits is relatively small. 

Fig. 56.2 Carotenoid biosynthesis pathway in plants. Enzymes (with abbreviations) indicated are isopentenyl pyrophosphate isomerase (IPI), geranylgeranyl pyrophosphate synthase (GGPS), phytoene synthase (PSY), phytoene desaturase (PDS), zeta-carotene desaturase (ZDS), carotenoid isomerase (CRTISO), lycopene beta-cyclase (LCYB), lycopene epsilon-cyclase (LCYE), beta-ring carotene hydroxylase (CHXB), epsilon-ring carotene hydroxylase (CHXE), zeaxanthin epoxidase (ZEP), violaxanthin de-epoxidase (VDE), capsorubin-capsanthin synthase (CCS), neoxanthin synthase (NXS), 9-cis epoxycarotenoid dioxygenase (NCED), and carotenoid cleavage dioxygenase (CCD). (Source [101], drawn using KeGG pathway)...

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