Kinetics of reformation of the S state capable of progressing to the S state after the O release by photosystem II.

The active site for water oxidation in photosystem II (PSII) comprises a MnCaO cluster adjacent to a redox-active tyrosine residue (Tyr). During the water-splitting process, the enzyme transitions through five sequential oxidation states (S to S), with O evolution occurring during the STyr· to STyr transition. Chloride also plays a role in this mechanism.

Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [PP].

Flash-induced absorption changes in the Soret region arising from the [PP] state, the chlorophyll cation radical formed upon light excitation of Photosystem II (PSII), were measured in Mn-depleted PSII cores at pH 8.6. Under these conditions, Tyr is i) reduced before the first flash, and ii) oxidized before subsequent flashes.

Tuning of the Chl and Chl properties in photosystem II by site-directed mutagenesis of neighbouring amino acids.

Photosystem II is the water/plastoquinone photo-oxidoreductase of photosynthesis. The photochemistry and catalysis occur in a quasi-symmetrical heterodimer, D1D2, that evolved from a homodimeric ancestor. Here, we studied site-directed mutants in PSII from the thermophilic cyanobacterium Thermosynechoccocus elongatus, focusing on the primary electron donor chlorophyll a in D1, Chl, and on its symmetrical counterpart in D2, Chl, which does not play a direct photochemical role.

Energetics and proton release in photosystem II from Thermosynechococcus elongatus with a D1 protein encoded by either the psbA or psbA gene.

In the cyanobacterium Thermosynechococcus elongatus, there are three psbA genes coding for the Photosystem II (PSII) D1 subunit that interacts with most of the main cofactors involved in the electron transfers. Recently, the 3D crystal structures of both PsbA2-PSII and PsbA3-PSII have been solved [Nakajima et al., J.

Photocatalytic generation of a non-heme Fe(iii)-hydroperoxo species with O in water for the oxygen atom transfer reaction.

Coupling a photoredox module and a bio-inspired non-heme model to activate O for the oxygen atom transfer (OAT) reaction requires a vigorous investigation to shed light on the multiple competing electron transfer steps, charge accumulation and annihilation processes, and the activation of O at the catalytic unit. We found that the efficient oxidative quenching mechanism between a [Ru(bpy)] chromophore and a reversible electron mediator, methyl viologen (MV), to form the reducing species methyl viologen radical (MV˙) can convey an electron to O to form the superoxide radical and reset an Fe(iii) species in a catalytic cycle to the Fe(ii) state in an aqueous solution. The formation of the Fe(iii)-hydroperoxo (Fe-OOH) intermediate can evolve to a highly oxidized iron-oxo species to perform the OAT reaction to an alkene substrate.