A specific carotenoid is required for reconstitution of the Rubrivivax gelatinosus B875 light harvesting complex from its subunit form B820.

The core light-harvesting complex B875 from Rubrivivax gelatinosus has been reconstituted from its subunit form B820 with hydroxyspheroidene, the carotenoid which is bound to native B875 antenna. Other carotenoids which are chemically similar to hydroxyspheroidene (spheroidene, spheroidenone, neurosporene and spirilloxanthin) gave only low levels of partial reconstitution. Absorption and circular dichroism spectra of the hydroxyspheroidene-containing, reconstituted B875 were identical with those of original B875 antenna isolated directly from chromatophores, indicating that the two hydroxyspheroidene molecules bind to their native sites within the (alpha beta)Bchl2 subunit during the reconstitution process. These observations point to a structural role for this carotenoid in determining the architecture of Rv. gelatinosus B875 antenna.