Spectral properties of reaction center preparations from Rhodopseudomonas spheroides.

The absorption, circular dichroism, and fluorescence spectra have been measured on oxidized and reduced reaction center preparations from Rhodopseudomonas spheroides strain R-26 at 295 and 77” K. The spectra indicate that the 4 bacteriochlorophyll a and 2 bacteriopheophytin a molecules in the reaction center are contained in a single pigment complex. The absorption bands at 893, 804, and ‘760 in the red and near-infrared each resolve into two separate CD maxima at 77’K. The interaction is very strong between the pigment molecules and their orientations are not coplanar. Oxidation of the reaction center bleaches the 893-nm absorption band of a bacteriochlorophyll dimer and the two corresponding CD maxima disappear. The changes in the low temperature fluorescence and CD spectra suggest that the molecular orientation may change when the reaction c’enter is oxidize&