Desaturases features

Efforts to test hypothesis two by biochemical reconstitution of a functional desaturase complex in vitro proved technically difficult and failed to provide a reproducible assay for functional expression of cloned lepidopteran desaturase sequences. In contrast, an in vivo expression system consisting of the yeast olel mutant and YEpOLEX plasmid confirmed hypothesis two and provided a technically facile and robust assay for determining the functional identities of many moth desaturase-encoding cDNAs. Particularly desirable features of this... 

Inhibitors of carotenoid synthesis also lead to chlorophyll destruction by destabilizing the photosynthetic apparatus. Total carotenoid content decreased with increased (-)-usnic concentration (Fig. 1.4). Carotenoid biosynthesis can be interrupted by inhibiting the enzyme phytoene desaturase that converts phytoene to carotenes or by inhibiting the enzyme HPPD responsible for plastoquinone (required for phytoene desaturase activity) synthesis.14 Usnic acid possesses some of the structural features of the triketone HPPD inhibitors, such as sulcotrione (Fig. 1.1C).8 (-)-Usnic acid had a strong inhibitory activity on HPPD, with an apparent IC50 of 70 nM, surpassing the activity obtained with the commercial herbicide sulcotrione (Fig. 1.5). 

The involvement of desaturase-type enzymes in the biosynthesis of some important lipidic antifeedants now has been firmly established (Fig. Ic) (7). An instructive example of this phenomenon is the production of ricinoleate (a purgative) by a desaturase homolog found in the castor plant. Here, a subtle variation in mechanistic pathway is responsible for the introduction of a C-12 hydroxyl group rather than a 12,13-double bond (7). Another interesting case features the putative dehydrogenation of a cyclopropyl fatty acid to produce sterculate, a potent inhibitor of the mammalian but not the plant A desaturase (8). Finally, the biosynthesis of polyacetylenes with antifungal properties such as falcarindiol is thought to involve a sequence of unique desaturase-mediated oxidations (9). 

All desaturases studied to date feature the syn removal of vicinal hydrogens as depicted in Fig. 2. For example, in the case of both soluble castor and membranous desaturases, it could be shown via the use of stereospecifically labeled substrates that dehydrogenation proceeds with removal of prof hydrogens at both C-9 and C-10 (15,16). This stereopreference seems highly conserved. A striking example of this phenomenon has been provided through extensive studies in the area of... 

If our hypothesis is correct, this hypothetical binding site should also accommodate fluridone, norflurazon and difunone and some possible binding orientations of these molecules are compared with furanone 13 in Figures 7-9. Note that we have attempted to depict the molecules in such a way that key structural features, e.g., the CF3 phenyl and vinylogous amide subunits, occupy the same positions as nearly as possible. Finally, it should be emphasized that considerable further work is required to demonstrate that the furanones actually inhibit phytoene desaturase and to further probe the possibility of a common binding site for the proven inhibitors including those such as fluorochloridone (10) and the m-phenoxybenzamides (4), which do not incorporate the vinylogous amide substructure. 

Another common feature among desaturases is an induction of these enzymes by peroxisome proliferators (PPs) (Kawashima et al., 1983 Kawashima et al., 1990). Fatty acids and their oxygenated derivates are examples of PPs known to be physiological activators of members of the PPAR family nuclear receptors (Willson et al., 2001). PP-activated receptor a (PPARa) is a transcription factor... 

Extreme response to dietary alterations is a remarkable feature of A desaturase (SCD-1). Liver SCD-1 mRNA is dramatically altered by dietary changes. 

Macdonald, M.L. Singaraja, R.R. Bissada, N. Ruddle, R Watts, R. Karasinska, J.M. Gibson, W.T. et al. Absence of stearoyl-CoA desaturase-1 ameloriates features of the metabolic syndrome in LDLR-defidentmice. J Lipid Res 2008,49, 217-229. 

XJLTRASTRUCTURAL FEATURES OF CHLOROPLASTS FROM FATTY ACID DESATURASE MUTANTS OF Arabidopsis thaliana. 

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