Circular dichroism of bacteriochlorophyll a in light-harvesting bacteriochlorophyll-protein complexes from Rhodopseudomonas palustris.

Bacteriochlorophyll (Bchl)-protein complexes containing light-harvesting Bchls were isolated from Rhodopseudomonas palustris, and the CD spectra of these complexes were measured in the near-infrared region. These isolated Bchl-protein complexes retained the CD signals of light-harvesting Bchls that were observed in intracytoplasmic membrane preparation. Comparison of the CD spectrum of B870-reaction center complexes with that of the isolated reaction centers revealed that the peak at 860 nm and the trough at 890 nm were attributable to the B870 spectral form, and that the peak at 790 nm and the trough at 810 nm were not all attributable to the reaction center. The CD spectra of spectrally different types of B800--850 complex revealed that the magnitudes of the peak at 840--850 nm and the trough at 860--870 nm were correlated with the magnitude of the absorption peak at around 850 nm. Therefore, these positive and negative CD bands were attributable to the B850 spectral form. In a similar manner, the peak at 810--820 nm and trough at 790 nm were attributable to the B800 spectral form.