Abstract
In two Rhodobacter and Rubrivivax, all of the carotenogenesis genes have been cloned and the characteristics of enzymes have been investigated. From these and the chemical structures of carotenoids, we can consider the carotenogenesis pathways and the enzymes in purple photosynthetic bacteria. When one enzyme in the normal spirilloxanthin pathway is lacking or is present with reduced activity, the pathway and the composition will be expected to change. These are named as the unusual spirilloxanthin pathways. When CrtI produces neurosporene, the final product is spheroidene. This is the spheroidene pathway, and the additional CrtA is always present. Accumulation of lycopene is due to reduced activity of CrtC. Rhodopin is accumulated in some species, and this is due to reduced activity of CrtD. In the case of the rhodopinal pathway, CrtD is inactive, and additional enzyme(s) to form aldehyde group is present.
