Phytoene geometrical isomers

Besides the capacity of CRTI to introduce all four double bonds in the conversion of phytoene to lycopene, the enzyme produces different geometric isomers than does PDS/ZDS (see graphic, side-by-side comparison in Fraser and Bramley ). CRTI produces all-trans isomers. Studies that have examined the function of the paired plant desaturases acting together, from Arabidopsis, and from maize and from... 

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).

Stereochemistry.—Geometrical Isomerism. Details of the synthesis and the spectroscopic and stereomutation properties of the a -trans- and 15-cw-isomers of phytoene [7,8,ll,12,7, 8, ir,12 -octahydro-i/f,i/r-carotene (23)] have been... 

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