The EXAFS study on the local structure of lanthanum in spinach PSII

The complex of photosystem II (PSII) had been prepared from spinach by treatment with Triton X-100. The PSII, which had been depleted of the extrinsic 17- and 23-kDa polypeptides, was obtained by exposing the solution to a high concentration of NaCl, and the complex of PSII-La3+ was prepared by treatment with LaCl3. The result indicated that La3+ could inhibit the oxygen-evolution activity of PSII by replacing the Ca2+. The local structural environment of La in PSII has been also studied by using extended X-ray absorption fine structure (EXAFS). The primary result of EXAFS indicated that La coordinated with eight oxygen and/or nitrogen atoms, with the distance of the La-O/N bond being 2.5 A. In addition, La coordinated with four carbon atoms, with a distance of 3.5 A in the second shell. In the third shell, La coordinated with two manganese atoms, with the distance of La-Mn bond being 4.49 A, and it was also found that the La-Mn distance (4.49 A) was longer than that of Ca-Mn (3.3 A) (1) in PSII.