Reflections on substrate water and dioxygen formation

This brief article aims at presenting a concise summary of all experimental findings regarding substrate water-binding to the Mn4CaO5 cluster in photosystem II. Mass spectrometric and spectroscopic results are interpreted in light of recent structural information of the water oxidizing complex obtained by X-ray crystallography, spectroscopy and theoreticalmodeling. Within this framework current proposals for themechanismof photosyntheticwater-oxidation are evaluated. This article is part of a Special Issue entitled:Metals in Bioenergetics and Biomimetics Systems.