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 cycli c electron flow and elevated B875 levels when grown at low oxygen tens ion. An examination of the low-temperature optical properties of chrom atophores from a pufX- strain, obtained by complementation of a pufLMX - mutant in trans with pufQBALM, encoding polypeptides of the B875 ant enna and reaction center complexes, revealed that the absorption and f luorescence emission maxima and the fluorescence polarization rise ove r the B875-Q, band were shifted to lower energies. These results sugge st that the pufX gene product may limit the aggregation state of the B 875 complex, assuring the proper functional arrangement of antenna and reaction center components within the cores of the photosynthetic uni ts.