Spirilloxanthin pathway

The Rhodospirillaceae and Chromatiaceae have the spirilloxanthin or the okenone pathway depending on the genus or species. All of the Ectothiorhodospiraceae have the spirilloxanthin pathway. The isorenieratene, the y-and -carotene, and the diapocarotene pathways are found specifically in the Chlorobiaceae, Chloroflexaceae, and Heliobacteriaceae, respectively. Aerobic photosynthetic bacteria mostly have the spirilloxanthin pathway, further most of these species have unusual carotenoids including non-photosynthetic carotenoids, such as carotenoid sulfates and carotenoic acids, which have no photosynthetic functions. 

Spirilloxanthin pathway (normal spirilloxanthin, unusual spirilloxanthin, spheroidene, and carotenal pathways). 

Most of the aerobic photosynthetic bacteria so far desaibed have the spirilloxanthin pathway, further some also have unusual carotenoids as described below. 

Carotenogenesis of the normal spirilloxanthin pathway is found in a large number of species of purple bacteria Rhodospirillaceae, Chromatiaceae and Ectothiorhodospiraceae (Tables 3-5). Spirilloxanthin is a symmetrical compound containing the methoxy groups at C-1 and C-1 and additional double bonds in the C-3,4 and C-3",4 positions. It has 13 conjugated double bonds (Fig. 4). 

Fig. 4. The predicted pathway for the biosynthesis of spirilloxanthin. Usually, the introduction of 2-keto is not involved in this pathway.

When one enzyme of the normal spirilloxanthin pathway is lacking or is present with reduced activity, the composition will be expected to change. Some species have indeed been reported to have such unusual compositions (Tables 3-5). Lycopene is... 

This spheroidene pathway is a variant of the unusual spirilloxanthin pathway as a result of the different properties of the phytoene desaturases (CrtI). 

The Chromatiaceae have either the spirilloxanthin pathway (normal spirilloxanthin, unusual spirilloxanthin and carotenal pathways) or okenone of the okenone pathway except for one species, Tea. halophila, which has both pathways (Tables 1 and4). Even in the same genus, some species have the spirilloxanthin pathway and others have the okenone pathway. Therefore, the carotenogenesis pathways are not well related to the bacteria s classification in the Chromatiaceae. 

Only the spirilloxanthin pathway is found (Tables 1 and 5). Some species have the unusual spirilloxanthin pathway. Hlr. halochloris and Hlr. abdel-malekii contain in addition carotenoid glycosides and their esters as major components. 

The tertiary methoxy and the cross-conjugated aldehyde groups have been found only in the carotenals of the purple photosynthetic bacteria, and the position of the aldehyde group in 1 0 is at C-19 instead of at C-20 as in the known carotenals. The half moieties of their molecules may be synthesized via a pathway of the normal spirilloxanthin series. The other half may be formed by cyclization and hydration as in 8 (FIG. l). 

Special isopiene rule, 2669 Specific doses, 2423 Specific symptrans, 2423 Spectral generalizatiSpectrophotometric methods, 2073 Sperm count, 2420, 2421 Spermidine, 1732 Spermine, 1732 Sperm production, 2418 Sphacelariaceae, 2900-2901 Sphacelariales, 2900-2901 Sphaerococcaceae, 2890 Sphaerococcus coronopifolius, 2890 Sphaerotrichia japonica (Sphaerotrichia divaricata), 2896 Spherisorb ODS2, 3393 Spheroidene, 3270, 3271 Spheromastigote, 845 Spinacea oleracea, 864 Spinacia oleracea, 3584 Spindle cell sarcoma 45, 992 Spinosin, 2163 Spiranoid 5-lactone, 3472 Spiranthera, 735 Spirilloxanthin, 3268, 3270, 3271 Spirilloxanthin pathways, 3268, 3270, 3271 Spirostanols, ilXl-ZXiO, il il, 3239,... 

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