Carotenoid biosynthesis cell-free systems

Reviews of the biosynthesis and distribution of carotenoids are available. Carotenoid biosynthesis by a cell-free system from Flavobacterium species has been briefly reported. ... 

A great diversity in molecular structure is observed among herbicides which inhibit carotene biosynthesis as is exemplified by the structures of norflurazon, fluridone and difunone (shown below). Nonetheless, many of these compounds, which comprise a subset of the larger group known as bleaching herbicides, appear to inhibit the same step in the biosynthetic pathway to the carotenoids (1 ). The inhibited step is the desaturation of 15-cis phytoene to 15- cis phytofluene (Figure 1) and the build-up of phytoene in plants and in cell-free systems which have been treated with these herbicides is well documented (2-4). 

Phytoene has been incorporated into carotenoids in several cell-free systems (Kushwaha et al., 1970, 1976 Subbarayanet al., 1970 Davies, 1973 Brown et al., 1975), and its position as an intermediate in the biosynthesis of more unsaturated carotenes is now well accepted. Previously some workers had concluded that phytoene did not behave as a precursor of carotenoids (for a review, see Britton, 1976a). This conclusion appears to have resulted from the accumulation of a metabolically inactive pool of phytoene in studies with inhibitors, and a failure of phytoene in this pool to be converted under certain conditions to carotenes on removal of the inhibitor. 

Enzyme Systems. Carotenoid biosynthesis by crude cell-free preparations from Halobacterium cutirubrum 0-carotene), Phycomyces blakesleeanus mutants (/8-carotene), and a Neurospora crassa mutant (phytoene) has been demonstrated. Detailed studies of carotenogenic enzymes from tomato fruit... 

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