Influence of iron-removal procedures on sequential electron transfer in photosynthetic bacterial reaction centers studied by transient EPR spectroscopy

Using electron spin polarized paramagnetic resonance (ESP EPR) spectroscopy, an investigation was made on the effect of the rate of primary charge separation, metal-site occupancy, and H-subunit content on the observed P865+QsubAsup- charge-separated state. Fe-removed and Zn-substituted reaction centers from Rhodopseudomonas sphaeroides R-26 were utilized to observe specific electron transfer rates (kQ) from the intermediate acceptor H- to the primary acceptor QA. Correlation of the transient EPR and optical results showed that the slow KQ rate in Fe-removed RCs was not dependent on the occupancy of the H-subunit or Fe-site.