DETERMINATION BY X-RAY-ABSORPTION OF REDOX-INDUCED STRUCTURAL-CHANGESIN 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 i n edge shape of F-x are interpreted to indicate structural changes of the iron-sulfur cluster in F-x upon reduction.