| 1. |
- Lohmiller, Thomas, et al.
(författare)
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An EPR and ENDOR spectroscopic investigation of the Ca2+-depleted oxygen-evolving complex of photosystem II
- 2013
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Ingår i: Photosynthesis research for food, fuel and future. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642320330 - 9783642320347 ; , s. 239-243
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Konferensbidrag (refereegranskat)abstract
- Multifrequency EPR and 55Mn ENDOR spectroscopy were used to characterize the S2′ state of the Ca2+- depleted oxygen-evolving complex. The 55Mn ENDOR spectrum of the S2′ state is broader than that of the native S2 state. Simulations of the data were performed using the spin Hamiltonian formalism. It was observed that the magnitudes of the four 55Mn hyperfine tensors (A1,iso≈ 300 MHz; A2, iso, A3, iso, A4, iso≈200MHz) are approximately the same as in the native S2 state. In addition, the geometries of the anisotropic hyperfine tensors are not changed. Thus, the same oxidation states are assigned to the Mn ions both in S2 and S2′ (MnA, MnB, MnC: IV, MnD: III). The isotropic hyperfine values of the individual Mn ions, especially A2, iso and A4 iso, do change upon Ca2+ depletion, indicating that, nonetheless, the electronic spin coupling scheme of the cluster is affected by Ca2+ removal.
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| 2. |
- Roberts, Irma N, et al.
(författare)
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PsbO degradation by deg proteases under reducing conditions
- 2013
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Ingår i: Photosynthesis research for food, fuel and future. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642320330 - 9783642320347 ; , s. 599-602
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Konferensbidrag (refereegranskat)abstract
- DegP/HtrA proteases are ATP-independent serine endopeptidases widely distributed in nearly all organisms. As yet, their physiological role in oxygenic photosynthetic organisms is unclear, although it has been widely speculated that they participate in the photosystem II repair cycle. Here, we investigated the ability of Deg proteases to degrade PsbO according to its redox state. A sample of purified PsbO or photosystem II complex was incubated together with recombinant Deg proteases of Synechocystis sp. PCC 6803 (HhoA, HhoB or HtrA). The reducing media was conferred by the Escherichia coli thioredoxin/thioredoxin reductase system. The results obtained showed that HhoA is able to hydrolyze reduced PsbO while HhoB and HtrA are not. HhoA was active against free PsbO of spinach as well as PsbO of Synechocystis attached to photosystem II, only under reducing conditions. The finding that all three Deg proteases of Synechocystis co-purify with photosystem II supports the hypothesis of PsbO as a substrate for Deg proteases in vivo.
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