[Absorption and fluorescence spectra and molecular organization of bacteriochlorophyll in reaction centers of Rhodopseudomonas spheroides].

Second derivative spectroscopy, computer curve analysis and Stepanov's equation show that the absorbance and fluorescence spectra of primary electron donor in reaction center of Rhodopseudomonas sphaeroides are splitting each into two asymmetric Gaussian components. Their absorption maxima at -196 degrees are 880 and 896 nm and emission maxima-906 and 923 nm, respectively. The absorption spectrum of Bchl-800 splits in the near infrared region into two bands with maxima at 790 and 803 nm. These components are ascribed to an exciton coupling in the two dimers of bacteriochlorophyll in the reaction center. The Qy transition moments of the two bacteriochlorophyll molecules of primary electron donor make an angle of 110 degrees and the angle between two Qy transitions of the pigment in Bchl-800 dimer is 150 degrees. The distance between the centers of chromophores in the dimers is estimated to be 8-11 A.