Carotene desaturase

A second class of herbicides primarily affects ( -carotene desaturase. These herbicides are apparent feedback inhibitors of PD as well. This class of compounds includes dihydropyrones like LS 80707 [90936-96-2] (56) and 6-methylpyridines (57,58). The third class consists of the ben2oylcyclohexane-diones, eg, 2-(4-chloro-2-nitroben2oyl)-5,5-dimethyl-cyclohexane-I,3-dione. This class of atypical bleaching herbicides induces phytoene accumulation when appHed either pre- or post-emergence. However, it does not inhibit phytoene desaturase activity in vitro (59). Amitrole also has been considered a bleaching herbicide, though its main mode of action is inhibition of amino acid synthesis. 

BARTLEY G E, SCOLNIK p A and BEYER p (1999) Two Arabidopsis thaliana carotene desaturases, ph)4oene desaturase and zeta-carotene desaturase, expressed in EicAencA/a coli, catalyze a poly-cis pathway to yield pro-lycopene , Eur JBiochem, 259, 396-403. 

LINDEN H, MISAWA N, SAITO T and SANDMANN G (1994) A uovel caroteuoid biosynthesis gene coding for -carotene desaturase functional expression, sequence and phylogenetic origin . Plant Mol Biol, 24, 369-79. 

Al-Babih, S., Hoa, T.T.C., and Schaub, R, Exploring the potential of the bacterial carotene desaturase CrtI to increase the beta-carotene content in Golden Rice, J. Exp. Bot. 57, 1007, 2006. 

Luo, R. and Wurtzel, E.T., A maize cDNA encoding zeta carotene desaturase (accession no. AE047490, PGR99-118), Plant Physiol. 120, 1206, 1999. 

Figure 73. The carotenoid biosynthetic pathway. Enzymes are named according to the designation of their genes Ccs, capsanthin-capsorubin synthase CrtL-b, lycopene-b-cyclase CrtL-e, lycopene-e-cyclase CrtR-b, b-ring hydroxylase, CrtR-e, e-ring hydroxylase DMADP, dimethylallyl diphosphate GGDP, geranylgeranyl diphosphate Ggps, geranylgeranyl-diphosphate synthase IDP, isopentenyl diphosphate Ipi, IDP isomerase Pds, phytoene desaturase Psy, phytoene synthase Vde, violaxanthin de-epoxidase Zds, z-carotene desaturase Zep, zeaxanthin epoxidase. (From van den Berg and others 2000.)...

Fig. 11.3 Simplified diagram of isoprenoid metabolic pathway relative to the conversions among carotenoids that have been genetically manipulated. Enzymes catalysing some key reactions are indicated by the following abbreviations IPI, isopentenyl pyrophosphate isomerase PSY, phytoene synthase PDS, phytoene desaturase (crti, gene from Erwinia uredovora) ZDS, -carotene desaturase LCYB, lycopene / -cyclase CRTR-b, /3-carotene 3,3 -hydroxylase CCS, capsanthin-capsombin synthase CRTO, /3-carotene ketolase.

Carotene desaturase catalyzes the final two desaturation steps to lycopene by introducing two double bonds at positions 7,8 of -carotene and 7, 8 of neurosporene. From cyanobacteria, two structurally unrelated genes for -carotene desaturase have been cloned. One crtQ (formerly called zds) from Anabaena is related to the bacterial crtI gene, whereas the second crtQb (also called crtQ-2) from Synechocystis is quite similar to crtP. 

Carotene desaturase inhibition by 4-(3-fluorophenyl)-3-(4-trifluoromefhyl-benzylthio)-4H-l,2,4-triazole (Y. Watanabe, Kyushu Univ., Japan). 

BREITENBACH, J., KUNTZ, M., TAKAICHl, S., SANDMANN, G., Catalytie properties of an expressed and purified higher plant type zeta-carotene desaturase from Capsicum annuum., Eur. J. Biochem. 1999, 265, 376-83. 

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)...

Continuing the pathway, 15-cA-phytoene would suffer then two desaturations carried out by phytoene desaturase, PDS [31], forming phytofluene and -carotene. Two subsequent desaturations are then performed by -carotene desaturase (ZDS) forming neurosporene and finally tetra-ds-lycopene (prolycopene). 

Carotene desaturase crtQ Green sulfin Chlorobaculum tepidum [31]... 

Bartley GE, Scolnik PA, Beyer P (1999) Two Arahidopsis thaliana carotene desatiunses, phytoene desaturase and -carotene desaturase, expressed in Escherichia coli, catalyze a poly-cii pathway to yield pro-lycopene. Fur J Biochem 259 396-403... 

Breitenbach J, Femandez-Gonzalez B, Vioque A, Sandmann G (1998) A higher-plant type -carotene desaturase in the cyanobacterium Synechocystis PCC6803. Plant Mol Biol 36 725-732... 

In the case of carotenoids, the main precursor phytoene is generated by action of phytoene synthase, strictly dependent upon Mn " enzyme, on geranylgeranyl pyrophosphate. Then, the desaturation of phytoene to lycopene involves four steps (Fig. 135.3) that are catalyzed by phytoene desaturase and -carotene desaturase. 

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