Release of Electrons and Protons from Substrate Water Molecules at the Oxygen-Evolving Complex in Photosystem II

Abstract

Oxygen evolution proceeds at the oxygen-evolving complex (OEC), the Mn4CaO5 cluster, in photosystem II (PSII), releasing protons and electrons from substrate water molecules. However, most mechanisms proposed for oxygen evolution is based on theoretical studies, where the deprotonation and oxidation sites of the Mn4CaO5 cluster are pre-assumed without analyzing the redox active site (e.g., redox potential) or the H-bond (e.g., pKa) for the release of the electrons or protons, respectively. Here, we summarize the characteristics of the OEC, focusing on the energetics of the electron-releasing and proton-releasing sites based on the PSII structure.