Determination by X-ray absorption of redox induced structural changes in iron-sulfur cluster F_x in photosystem I

X-ray absorption spectra of photosystem I core protein containing F_x, the low potential iron-sulfur cluster was measured. X-ray absorption of the iron K-edge was obtained in the reduced and oxidized forms of F_x. An edge shift of 0.5 eV to lower energy and a change in the X-ray absorption near edge structure was observed. Some of the alterations in edge shape of F_x are interpreted to indicate structural changes of the iron-sulfur cluster in F_x upon reduction.