title: Detection of an intermediary, protonated water cluster in photosynthetic oxygen evolution.
abstract: In photosynthesis, photosystem II evolves oxygen from water by the accumulation of photooxidizing equivalents at the oxygen-evolving complex (OEC). The OEC is a Mn4CaO5 cluster, and its sequentially oxidized states are termed the Sn states. The dark-stable state is S1, and oxygen is released during the transition from S3 to S0. In this study, a laser flash induces the S1 to S2 transition, which corresponds to the oxidation of Mn(III) to Mn(IV). A broad infrared band, at 2,880 cm(-1), is produced during this transition. Experiments using ammonia and (2)H2O assign this band to a cationic cluster of internal water molecules, termed "W5(+)." Observation of the W5(+) band is dependent on the presence of calcium, and flash dependence is observed. These data provide evidence that manganese oxidation during the S1 to S2 transition results in a coupled proton transfer to a substrate-containing, internal water cluster in the OEC hydrogen-bonded network.
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
authors.forename: Brandon C
authors.initials: BC
authors.lastname: Polander
authors.forename: Bridgette A
authors.initials: BA
authors.lastname: Barry
mesh_terms: D055592:Biophysical Phenomena; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism; D011522:Protons; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism; D014867:Water / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D011522:Protons; D014867:Water; D008345:Manganese; D010100:Oxygen; D002118:Calcium