Probing light-induced changes in the local structure of Fe in photosynthetic reaction centers by differential turbo – XAFS. SC-3449

Spectroscopic and X ray diffraction data indicate that, following photoexcitation, the photosynthetic reaction center (RC) undergoes conformational changes which stabilize the light-induced electric charge separation catalyzed by this pigment-protein complex. Within the RC a non-heme Fe2+ atom is located in a key domain which has been proposed to undergo structural rearrangements following electron transfer. We aimed at detecting light-induced changes in the local structure of the Fe2+ atom by using differential turbo – XAFS on the ID24 beamline, exploiting the extreme stability of the set – up. Preliminary analysis of XANES spectra acquired during dark-light cycles indicate reversible changes, most likely related to light-induced conformational relaxations. However, prolonged exposition to excitation light during the course of the experiment causes additional XANES alterations, ascribed to irreversible changes of the native local structure and/or redox state of the Fe2+ atom.