Hiroshi Ishikita

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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)
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)
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)
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)
Photosynthetic reaction centers from Blastochloris viridis possess Tyr-L162 located mid-way between the special pair chlorophyll (P) and the heme (heme3). While mutation of the tyrosine does not affect the kinetics of electron transfer from heme3 to P, recent time-resolved Laue diffraction studies reported displacement of Tyr-L162 in response to the(More)
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