Electrostatic role of the non‐heme iron complex in bacterial photosynthetic reaction center

To elucidate the role of the non‐heme iron complex (Fe‐complex) in the electron transfer (ET) events of bacterial photosynthetic reaction centers (bRC), we calculated redox potentials of primary/secondary quinones Q A/B ( E m (Q A/B )) in the Fe‐depleted bRC. Removing the Fe‐complex, the calculated E m (Q A/B ) are downshifted by ∼220 mV/∼80 mV explaining both the 15‐fold decrease in ET rate from bacteriopheophytin ( H A ‐ ) to Q A and triplet state occurrence in Fe‐depleted bRC. The larger downshift in E m (Q A ) relative to E m (Q B ) increases the driving‐energy for ET from Q A to Q B by 140 meV, in agreement with ∼100 meV increase derived from kinetic studies.