Oxygen-oxygen bond formation and O2 generation occur from the S4 state of the oxygen-evolving complex (OEC). Several mechanistic possibilities have been proposed for water oxidation, depending on the formal oxidation state of the Mn atoms. All fall under two general classifications: the AB mechanism in which nucleophilic oxygen (base, B) attacks electrophilic oxygen (acid, A) of the Mn4Ca clust...

A new hypothetical mechanism is proposed for photoassembly of the (Mn)4-cluster of the photosynthetic oxygen evolving complex (OEC). In this process, a neutral radical of Y(Z) tyrosine plays a role in oxidizing Mn2+ associated with an apo-OEC, and also in abstracting a proton from a water molecule bound to the Mn2+ ion, together with D1-His190. This is in a similar fashion to the metallo-radica...

Within photosynthetic organisms, the oxygen-evolving complex (OEC) of photosystem II generates dioxygen from water using a catalytic Mn(4)CaO(n) cluster (n varies with the mechanism and nature of the intermediate). We report here the rational synthesis of a [Mn(3)CaO(4)](6+) cubane that structurally models the trimanganese-calcium-cubane subsite of the OEC. Structural and electrochemical compar...

The oxygen evolving complex (OEC) of photosystem II (PSII) requires chloride as a critical cofactor. The Cl content of PSII was determined to be 1 Cl/PSII by the AgCl colloid assay. The dissociation constant for Cl in NaCl-washed PSII was determined using the Cl sensitive microelectrode. Two classes of Cl binding sites were found with Kd values of 53 μM and 4.2 mM. The effects of anions on the ...

The oxygen in the atmosphere is derived from light-driven oxidation of water at a catalytic centre contained within a multi-subunit enzyme known as photosystem II (PSII). PSII is located in the photosynthetic membranes of plants, algae and cyanobacteria and its oxygen-evolving centre (OEC) consists of four manganese ions and a calcium ion surrounded by a highly conserved protein environment. Re...

Redox-inactive metal ions play crucial roles in tuning the reactivity of oxygen-containing metal complexes and metalloenzymes such as the oxygen-evolving complex (OEC) in photosystem II (PSII) and its small-molecule mimics. In PSII, a Ca ion is part of the tetrameric Mn cluster, Mn4CaO5, and is integral to the water oxidation catalysis and evolution of oxygen by the OEC. Several different funct...

We have examined the assembly of the nuclear-encoded subunits of the oxygen-evolving complex (OEC) after their import into isolated intact chloroplasts. We showed that all three subunits examined (OE33, OE23, and OE17) partition between the thylakoid lumen and a site on the inner surface of the thylakoid membrane after import in a homologous system (e.g., pea or spinach subunits into pea or spi...

A novel family of heteronuclear Mn(IV)Ca-oxido complexes containing Mn(IV)Ca-oxido cuboidal moieties and reactive water molecules on Ca(2+) have been synthesized and characterized to mimic the oxygen-evolving complex (OEC) of photosystem II (PSII) in nature.

The oxygen-evolving complex (OEC) in photosystem II (PS II) was studied in the S0 through S3 states using 1s2p resonant inelastic X-ray scattering spectroscopy. The spectral changes of the OEC during the S-state transitions are subtle, indicating that the electrons are strongly delocalized throughout the cluster. The result suggests that, in addition to the Mn ions, ligands are also playing an ...

In photosystem II, oxygen evolution occurs by the accumulation of photo-induced oxidizing equivalents at the oxygen-evolving complex (OEC). The sequentially oxidized states are called the S(0)-S(4) states, and the dark stable state is S(1). Hydrogen bonds to water form a network around the OEC; this network is predicted to involve multiple peptide carbonyl groups. In this work, we tested the id...