PIGMENT ASSIGNMENT IN THE ABSORPTION-SPECTRUM OF THE PHOTOSYSTEM-II REACTION-CENTER BY SITE-SELECTION FLUORESCENCE SPECTROSCOPY

The steady state fluorescence properties of the photosystem II reactio n center (D-1-D-2-cyt-b(559) complex, PSII-RC) have been investigated by site-selection spectroscopy. The pattern of the vibronic bands in t he emission spectra is used to identify the fluorescing species that h ave their absorption maxima on the red edge of the spectrum (at around 682 nm). At 10 K, even samples with a low content of red absorbing ch lorophyll a (Chi) show pure Chi emission upon excitation at 685 nm, wh ereas at 77 K the fluorescence of the PSII-RCs is contributed to by Ch i and pheophytin a (Pheo) in a ratio of roughly 8:2. These results all ow an unequivocal distinction between two different spectral decomposi tions that were recently suggested for the absorption spectrum of the PSII-RC [Konermann, L., & Holzwarth, A. R. (1996) Biochemistry 35, 829 ]. Only one of these decompositions is compatible with the experimenta l data presented here according to which the absorption on the red edg e of the spectrum is dominated by an accessory Chi.