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 caroteno ids which are chemically similar to hydroxyspheroidene (spheroidene, s pheroidenone, neurosporene and spirilloxanthin) gave only low levels o f partial reconstitution. Absorption and circular dichroism spectra of the hydroxyspheroidene-containing, reconstituted B875 were identical with those of original B875 antenna isolated directly from chromatopho res, indicating that the two hydroxyspheroidene molecules bind to thei r native sites within the (alpha/beta)Bchl(2) subunit during the recon stitution process. These observations point to a structural role for t his carotenoid in determining the architecture of Rv. gelatinosus B875 antenna.