FIGURE 1.

Experiments (21) and calculations of optical difference spectra of PS-II core complexes from Thermosynechococcus elongatus. The calculations were performed using the site energies determined previously (18), except for Chl_D1 which was shifted by 4 nm to the red. The corresponding wavelengths assigned to each pigment are P_D1, 666 nm; P_D2, 666 nm; Chl_D1, 682 nm; Chl_D2, 667 nm; Pheo_D1, 672 nm; and Pheo_D2, 675 nm. The two experimental T-S spectra (bottom panel) were obtained for singly (open squares) and doubly (solid circles) reduced Q_A. In the latter case it is also possible that Q_A has dissociated from the core complex.