Assembly of Manganese-Oxo Clusters in Solution as Models for the Photosynthetic Oxygen-Evolving Complex

摘要

The four-electron oxidation of water to form O_2 in photosynthesis is a light-driven process that occurs in the multi-subunit membrane protein Photosystem II (PSII). The reaction is catalyzed by an inorganic cluster known as the Oxygen Evolving Complex (OEC), which has a composition of Mn_4O_xCaCl_y. A preliminary X-ray crystal structure of PSn has recently been determined, but the nature of the ligands bound to the manganese ions and the internal structure of the core were not fully revealed. Insight into the structure of the OEC has been gained primarily through X-ray absorption spectroscopy (XAS) and spin resonance techniques (EPR/ENDOR) (reviewed in [3]). Based on these data, a number of candidate structures for the Mn_4O_x subcore were described, of which the two leading candidates are the Mn_4O_4-funnel and the Mn_4O_4/Mn_4O_2-butterfly subcores (Figure 1).