Comparison of the Manganese Cluster in Oxygen-Evolving Photosystem II with Distorted Cubane Manganese Compounds through X-ray Absorption Spectroscopy.

X-ray absorption spectroscopy has been employed to assess the degree of similarity between the oxygen-evolving complex (OEC) in photosystem II (PS II) and a family of synthetic manganese complexes containing the distorted cubane [Mn(4)O(3)X] core (X = benzoate, acetate, methoxide, hydroxide, azide, fluoride, chloride, or bromide). These [Mn(4)(&mgr;(3)-O)(3)(&mgr;(3)-X)] cubanes possess C(3)(v)() symmetry except for the X = benzoate species, which is slightly more distorted with only C(s)() symmetry. In addition, Mn(4)O(3)Cl complexes containing three or six terminal Cl ligands at three of the Mn were included in this study.

Structural Change of the Mn Cluster during the S→S State Transition of the Oxygen-Evolving Complex of Photosystem II. Does It Reflect the Onset of Water/Substrate Oxidation? Determination by Mn X-ray Absorption Spectroscopy.

The oxygen-evolving complex of Photosystem II in plants and cyanobacteria catalyzes the oxidation of two water molecules to one molecule of dioxygen. A tetranuclear Mn complex is believed to cycle through five intermediate states (S-S) to couple the four-electron oxidation of water with the one-electron photochemistry occurring at the Photosystem II reaction center. We have used X-ray absorption spectroscopy to study the local structure of the Mn complex and have proposed a model for it, based on studies of the Mn K-edges and the extended X-ray absorption fine structure of the S and S states.

Strontium EXAFS Reveals the Proximity of Calcium to the Manganese Cluster of Oxygen-Evolving Photosystem II.

The oxygen-evolving complex of Photosystem II (PS II) in green plants and algae contains a cluster of four manganese atoms in the active site, which catalyzes the photoinduced oxidation of water to dioxygen. Along with Mn, calcium and chloride ions are necessary cofactors for proper functioning of the complex. A key unresolved question is whether Ca is close to the Mn cluster, within about 3.

Structural Effects of Calcium Depletion on the Manganese Cluster of Photosystem II: Determination by X-ray Absorption Spectroscopy.

The structural consequences of calcium depletion of Photosystem II (PS II) by treatment at pH 3.0 in the presence of citrate has been determined by Mn K-edge X-ray absorption spectroscopy. X-ray absorption edge spectroscopy of Ca-depleted samples in the S', S', and S' oxidation states reveals that there is Mn oxidation on the S'-S' transition, although no evidence of Mn oxidation was found for the S'-S' transition.