A novel sequence for phytoene dehydrogenation in Rhodospirillum rubrum

Differences between the absorption spectra of zeta-carotene (7,8,7',8'-tetrahydrolycopene) and the corresponding conjugated heptaene from diphenylamine-inhibited cultures of Rhodospirillum rubrum have been rationalized by the identification of the latter compound as the unsymmetrical isomer, 7,8,11,12-tetrahydrolycopene. The structures of the other conjugated polyene hydrocarbons, phytoene, phytofluene and neurosporene, have been confirmed and a novel pathway for the dehydrogenation of phytoene to lycopene in these bacteria is described.