AN EXAFS STUDY OF THE MANGANESE O2-EVOLVING COMPLEX IN PURIFIED PHOTOSYSTEM-II MEMBRANE-FRACTIONS - THE S1 AND S2 STATES

Manganese K-edge X-ray spectra have been obtained for Photosystem II samples isolated using Triton X-100 detergent and samples further purified by n-heptyl beta-D-thioglucoside detergent treatment to remove light-harvesting polypeptides and low-affinity calcium. The structure of the manganese complex is very similar for the two detergent preparations used. Analysis of the e.x.a.f.s. spectra for samples in the S1 and S2 states indicate changes in bond lengths for the shells of oxygen/nitrogen atoms. For the S1 state, oxygen shells at 0.181 and 0.193 nm (1.81 and 1.93 angstrom) were observed and one manganese shell at 0.270 nm (2.70 angstrom). In the S2 state the oxygen bond lengths are longer at 0.184 and 0.200 nm (1.84 and 2.00 angstrom). Additionally a shell of scatterers at 0.37 nm (3.7 angstrom) was observed in both states which could be fitted to models with calcium scatterers at this distance.