Photosystem II: The Reaction Center of Oxygenic Photosynthesis ∗ David J. Vinyard, 1, 2 Gennady M. Ananyev, 1 and G. Charles Dismukes 1 1 Department of Chemistry and Chemical Biology and the Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854; email: ananyev@rci.rutgers.edu, dismukes@rci.rutgers.edu 2 Department of Chemistry, Princeton University, Princeton, New Jersey 08540; email: dvinyard@princeton.edu Annu. Rev. Biochem. 2013. 82:577–606 First published online as a Review in Advance on March 18, 2013 The Annual Review of Biochemistry is online at biochem.annualreviews.org This article’s doi: 10.1146/annurev-biochem-070511-100425 Copyright c  2013 by Annual Reviews. All rights reserved ∗ This article is dedicated to the memory of Professor Gernot Renger, pioneer in photosystem II research. Keywords oxygen evolution, photoassembly, photoprotection, proton-coupled electron transport, period-four oscillations, water oxidation kinetics, water oxidation thermodynamics Abstract Photosystem II (PSII) uses light energy to split water into chemi- cal products that power the planet. The stripped protons contribute to a membrane electrochemical potential before combining with the stripped electrons to make chemical bonds and releasing O 2 for power- ing respiratory metabolisms. In this review, we provide an overview of the kinetics and thermodynamics of water oxidation that highlights the conserved performance of PSIIs across species. We discuss recent ad- vances in our understanding of the site of water oxidation based upon the improved (1.9- ˚ A resolution) atomic structure of the Mn 4 CaO 5 water- oxidizing complex (WOC) within cyanobacterial PSII. We combine these insights with recent knowledge gained from studies of the bio- genesis and assembly of the WOC (called photoassembly) to arrive at a proposed chemical mechanism for water oxidation. 577 Annu. Rev. Biochem. 2013.82:577-606. Downloaded from www.annualreviews.org by Rutgers University Libraries on 06/09/13. For personal use only.