Absorption and fluorescence spectra of light-harvesting bacteriochlorophyll-protein complexes from Rhodopseudomonas palustris in the near-infrared region

Bacteriochlorophyll (Bchl)-protein complexes were isolated from Rhodopseudomonas palustris. Detergent treatment and polyacrylamide gel electrophoresis under rather mild conditions resulted in clear separation of light-harvesting Bchls into B870 Bchls and B800-850 Bchls as two distinctly different protein complexes. It was shown that almost all the Bchl contained in intracytoplasmic membranes was recovered as either B870-reaction center complexes or B800-850 complexes without loss of Bchls as free pigments. Furthermore, it was shown that the spectral form of each type of Bchl was not altered by this procedure for isolation, as judged by the calculated absorption spectrum which was the sum of the absorption spectra of the isolated complexes. Fluorescence measurement of the isolated complexes and intracytoplasmic membranes not only supported these ideas, but also indicated that the excited state was actually transferred from B800-850 Bchls to B870 Bchls. The isolation and measurements of absorption and fluorescence were carried out on spectrally different types of intracytoplasmic membrane from cells cultured under different culture conditions. The B870-reaction center complexes from different types of intracytoplasmic membrane were spectrally identical. The B800-850 complexes were widely different in absorption spectra, especially in the ratios of peaks at 800 and 850 nm, but exhibited similar fluorescence spectra.