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Photosystem II uses light to drive water oxidation and plastoquinone (PQ) reduction. PQ reduction involves two PQ cofactors, Q(A) and Q(B), working in series. Q(A) is a one-electron carrier, whereas Q(B) undergoes sequential reduction and protonation to form Q(B)H(2). Q(B)H(2) exchanges with PQ from the pool in the membrane. Based on the atomic coordinates(More)
Using quantum mechanics/molecular mechanics calculations and the 1.9-Å crystal structure of Photosystem II [Umena Y, Kawakami K, Shen J-R, Kamiya N (2011) Nature 473(7345):55-60], we investigated the H-bonding environment of the redox-active tyrosine D (TyrD) and obtained insights that help explain its slow redox kinetics and the stability of TyrD(•). The(More)
The primary electron donor P700 in photosystem I is composed of two chlorophylls, P(A) and P(B). P700 forms the cationic [P(A)/P(B)](•+) state as a result of light-induced electron transfer. We obtained a P(A)(•+)/P(B)(•+) ratio of 28:72 and a spin distribution of 22:78 for the entire PSI protein-pigment complex. By considering the influence of the protein(More)
Influence of the axial ligand of PD1 chlorophyll (D1-His-198) on the Em of monomer chlorophylls PD1 and PD2, and the PD1•+/PD2•+ charge ratio was investigated by theoretical calculations using the PSII crystal structure of Thermosynechococcus vulcanus analyzed at 1.9-Å resolution. It was found that the Em(PD1)/Em(PD2) values and PD1•+/PD2•+ ratio remained(More)
In photosystem II (PSII), the Mn4CaO5 cluster catalyses the water splitting reaction. The crystal structure of PSII shows the presence of a hydrogen-bonded water molecule directly linked to O4. Here we show the detailed properties of the H-bonds associated with the Mn4CaO5 cluster using a quantum mechanical/molecular mechanical approach. When O4 is taken as(More)
Most of the chlorophyll (Chl) cofactors in photosystem II (PSII) from Acaryochloris marina are Chld, although a few Chla molecules are also present. To evaluate the possibility that Chla may participate in the P(D1)/P(D2) Chl pair in PSII from A. marina, the P(D1)(•+)/P(D2)(•+) charge ratio was investigated using the PSII crystal structure analyzed at 1.9-Å(More)
The photoactive chromophore of photoactive yellow protein (PYP) is p-coumaric acid (pCA). In the ground state, the pCA chromophore exists as a phenolate anion, which is H-bonded by protonated Glu46 (O(Glu46)-O(pCA)=~2.6Å) and protonated Tyr42. On the other hand, the O(Glu46)-O(pCA) H-bond was unusually short (O(Glu46)-O(pCA)=2.47Å) in the intermediate(More)
Quinones can accept two electrons and two protons, and are involved in electron transfer and proton transfer reactions in photosynthetic reaction centers. To date, the pK a of these quinones in aqueous solution have not been reported. We calculated the pK a of the initial protonation (Q·− to QH·) and the second protonation (QH− to QH2) of 1,4-quinones using(More)
In the cyanobacterial photosystem II (PSII), the O4-water chain in the D1 and CP43 proteins, a chain of water molecules that are directly H-bonded to O4 of the Mn4Ca cluster, is linked with a channel that connects the protein bulk surface along with a membrane-extrinsic protein subunit, PsbU (O4-PsbU channel). The cyanobacterial PSII structure also shows(More)
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