Background: Photosystem II, the water-splitting enzyme, includes a protein, D1, which can be coded by three different psbA genes in Thermosynechococcus elongatus. Results: In PsbA2-PSII, the environment of Tyr Z is different from that in PsbA1-PSII and PsbA3-PSII. Conclusion: The geometry of the Tyr Z -O⅐⅐⅐H⅐⅐⅐N⑀-His-190 bonding is an important parameter for PSII activity. Significance: The environment of the cofactors is involved in the tuning of the electron transfer efficiency.

The sensitivity to high light conditions of Photosystem II with either PsbA1 (WT*1) or PsbA3 (WT*3) as the D1 protein was studied in whole cells of the thermophilic cyanobacterium Thermosynechococcus elongatus. When the cells are cultivated under high light conditions the following results were found: (i) The O(2) evolution activity decreases faster in WT*1 cells than in WT*3 cells both in the absence and in the presence of lincomycin, a protein synthesis inhibitor; (ii) In WT*1 cells, the rate constant for the decrease of the O(2) evolution activity is comparable in the presence and in the absence of lincomycin; (iii) The D1 content revealed by western blot analysis decays similarly in both WT*1 and WT*3 cells and much slowly than O(2) evolution; (iv) The faster decrease in O(2) evolution in WT*1 than in WT*3 cells correlates with a much faster inhibition of the S(2)-state formation; (v) The shape of the WT*1 cells is altered. All these results are in agreement with a photo-inhibition process resulting in the loss of the O(2) activity much faster than the D1 turnover in PsbA1-PSII and likely to a greater production of reactive oxygen species under high light conditions in WT*1 than in WT*3. This latter result is discussed in view of the known effects of the PsbA1 to PsbA3 substitution on the redox properties of the Photosystem II cofactors. The observation that under low light conditions WT*3 cells are able to express the psbA(3) gene, whereas under similar conditions wild type cells are expressing mainly the psbA(1) gene is also discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Bacteriorhodopsin (bR) in a purple membrane of H. salinarum shows a light-driven proton pump activity under photo-irradiation. In the photocycle, it is difficult to trap O intermediate and hence its detailed structure has not revealed yet. Here, we demonstrate that the O-like intermediate in Y185F mutant can be stationary trapped by in-situ photoirradiation solid-state NMR. In the dark adapted state, 13 C NMR spectrum of [15, UV in sunlight causes formation of crosslinks between two adjacent pyrimidine bases in DNA, namely cyclobutane pyrimidine dimers (CPDs) and pyrimidine(6-4)pyrimidone photoproducts ((6-4)PPs). Since these lesions lead to mutagenesis and cell death, organisms have developed UVprotecting systems that can remove the UV lesions and restore intact nucleobases. The (6-4) photolyase is a unique flavoenzyme that can repair the (6-4)PP by utilizing blue light. We have recently reported that the repair of the (6-4)PP by the (6-4) photolyase requires two photons. In this study, we investigated the role of the amino acid residues located proximal to the lesion and performed biochemical and spectroscopic studies. Their molecular role in the two-photon DNA repair will be discussed. 2P250Theoretical study of the electron transfer reaction by DNA The DNA photolyase repairs thymine dimers found in UV-induced DNA lesions by electron transfer reaction. In this work, the molecular mechanism involved in the efficient electron transfer of DNA photolyase was investigated by the analysis of electron tunneling pathways from FADH-to CPD using ab initio and fragment molecular orbital calculations.In particular, we focused on the roles of amino acid residues and crystallographic water molecules in the active site. According to previous studies, the calculation of electron transfer pathways, considering excited state of FADH-and three amino acids (Gln283, Asn349 and Met353), have not been performed. We computed the electron transfer pathways from FADH-to CPD using ab initio and fragment molecular orbital method. We report bio-inorganic hybrid electrodes consisting of Photosystem II (PSII) and layered double hydroxides (LDHs) for visible light-driven water oxidation. PSII is a photosynthetic protein, which catalyzes the oxidation of water to molecular oxygen under visible light irradiation. LDHs are composed of cationic double hydroxide nanosheets and anions placed in the interlayers of the cationic nanosheets. We synthesized PSII-LDH electrodes and recorded their photocurrent in a buffered aqueous solution at pH 6.5 under visible light irradiation. In our system efficient interfacial electron transfer occurred from PSII to LDH, allowing us to experimentally determine turnover numbers of PSII in vitro for the first time. 2P252光化学系 II における TyrZ -D1/His190 の距離と PCET の 関係