Implications of spin dynamics for the charge recombination in iron-depleted and quinone-substituted reaction centers from Rhodobacter sphaeroides R-26

Detailed calculations on the spin-dependent recombination dynamics are presented for reaction centers of Rhodobacter sphaeroides R-26 in which electron transfer from the primary radical pair to the iron-quinone acceptor complex has been slowed down by either iron depletion or replacement of the native ubiquinone by other quinones with different midpoint potential. Recombination yields reported for iron-depleted samples (Kirmaier, C., Holten, D., Debus, R.J., Feher, G. and Okamura, M.Y. (1986) Proc. Natl. Acad. Sci. USA 83, in the press) are compared to those in quinone-depleted reaction centers, where the forward electron transfer is completely blocked by extraction of the quinone. Within the scatter of the experimental data, the recombination pattern appears to be similar in the two different preparations indicating that the structural and kinetic features of the recombining radical pair state are not seriously affected by removal of the iron.