ALTERED SPECTRAL PROPERTIES OF THE B875 LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEX IN A RHODOBACTER-SPHAEROIDES MUTANT LACKING PUFX

Mutants of Rhodobacter sphaeroides lacking the pufX gene are unable to grow photosynthetically and have been reported to show impaired cyclic electron flow and elevated B875 levels when grown at low oxygen tension. An examination of the low-temperature optical properties of chromatophores from a pufX- strain, obtained by complementation of a pufLMX- mutant in trans with pufQBALM, encoding polypeptides of the B875 antenna and reaction center complexes, revealed that the absorption and fluorescence emission maxima and the fluorescence polarization rise over the B875-Q, band were shifted to lower energies. These results suggest that the pufX gene product may limit the aggregation state of the B875 complex, assuring the proper functional arrangement of antenna and reaction center components within the cores of the photosynthetic units.