PARENT SESSION
Plenary Lectures 4
Thursday September 2nd, 2004 8:30 AM Room 210A

Oxygen evolution. Gary Brudvig^*,1, ¹ Department of Chemistry, New Haven, CT, USA

ABSTRACT- Photosystem II (PSII) uses light energy to split water into protons, electrons and molecular oxygen. In this reaction, Nature has solved the difficult chemical problem of efficient four-electron oxidation of water to yield oxygen without significant amounts of reactive intermediate species such as superoxide, hydrogen peroxide and hydroxyl radicals. In order to use Nature's solution for the design of artificial catalysts that split water, it is important to understand the mechanism of the reaction. The recently published 3.5 angstrom resolution X-ray crystal structure of a cyanobacterial PSII provides a detailed model of the manganese and calcium ions, the redox-active tyrosine called Y_Z, and the surrounding amino acids that comprise the oxygen-evolving complex (OEC) [K. N. Ferreira et al., Science (2004) 203, 1831]. The revealed geometry of the OEC lends weight to certain hypothesized mechanisms for oxygen evolution, including the one propounded by our group [J. S. Vrettos et al., Biochim. Biophys. Acta (2001) 1503, 229]. The water-splitting mechanism of PSII will be discussed in the light of biophysical studies, inorganic chemistry and the new crystallographic information. This enables detailed suggestions concerning the mechanistic functions (particularly the redox and proton-transfer roles) of calcium, chloride and certain amino acids in and around the OEC. Supported by the National Institutes of Health (GM32715).

KEY WORDS: oxygen evolution, photosystem II, manganese