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- de Lichtenberg, Casper, et al.
(author)
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The D1-V185N mutation alters substrate water exchange by stabilizing alternative structures of the Mn4Ca-cluster in photosystem II
- 2021
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In: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier. - 0005-2728 .- 1879-2650. ; 1862:1
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Journal article (peer-reviewed)abstract
- In photosynthesis, the oxygen-evolving complex (OEC) of the pigment-protein complex photosystem II (PSII) orchestrates the oxidation of water. Introduction of the V185N mutation into the D1 protein was previously reported to drastically slow O2-release and strongly perturb the water network surrounding the Mn4Ca cluster. Employing time-resolved membrane inlet mass spectrometry, we measured here the H218O/H216O-exchange kinetics of the fast (Wf) and slow (Ws) exchanging substrate waters bound in the S1, S2 and S3 states to the Mn4Ca cluster of PSII core complexes isolated from wild type and D1-V185N strains of Synechocystis sp. PCC 6803. We found that the rate of exchange for Ws was increased in the S1 and S2 states, while both Wf and Ws exchange rates were decreased in the S3 state. Additionally, we used EPR spectroscopy to characterize the Mn4Ca cluster and its interaction with the redox active D1-Tyr161 (YZ). In the S2 state, we observed a greatly diminished multiline signal in the V185N-PSII that could be recovered by addition of ammonia. The split signal in the S1 state was not affected, while the split signal in the S3 state was absent in the D1-V185N mutant. These findings are rationalized by the proposal that the N185 residue stabilizes the binding of an additional water-derived ligand at the Mn1 site of the Mn4Ca cluster via hydrogen bonding. Implications for the sites of substrate water binding are discussed.
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| 2. |
- Ermakova, Maria, et al.
(author)
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Upregulation of bundle sheath electron transport capacity under limiting light in C-4 Setaria viridis
- 2021
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In: The Plant Journal. - : John Wiley & Sons. - 0960-7412 .- 1365-313X. ; 106:5, s. 1443-1454
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Journal article (peer-reviewed)abstract
- C-4 photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO2 concentration at the site of CO2 fixation. C-4 plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity. Plants grown under low light (LL) maintained CO2 assimilation rates similar to high light plants but had an increased chlorophyll and light-harvesting-protein content, predominantly in BS cells. Photosystem II (PSII) protein abundance, oxygen-evolving activity and the PSII/PSI ratio were enhanced in LL BS cells, indicating a higher capacity for linear electron flow. Abundances of PSI, ATP synthase, Cytochrome b(6)f and the chloroplast NAD(P)H dehydrogenase complex, which constitute the BS cyclic electron flow machinery, were also increased in LL plants. A decline in PEP carboxylase activity in mesophyll cells and a consequent shortage of reducing power in BS chloroplasts were associated with a more oxidised plastoquinone pool in LL plants and the formation of PSII - light-harvesting complex II supercomplexes with an increased oxygen evolution rate. Our results suggest that the supramolecular composition of PSII in BS cells is adjusted according to the redox state of the plastoquinone pool. This discovery contributes to the understanding of the acclimation of PSII activity in C-4 plants and will support the development of strategies for crop improvement, including the engineering of C-4 photosynthesis into C-3 plants.
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| 3. |
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| 4. |
- Wang, Huan, et al.
(author)
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A conducting additive-free high potential quinone-based conducting redox polymer as lithium ion battery cathode
- 2021
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 391
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Journal article (peer-reviewed)abstract
- Organic carbonyl compounds have been considered as promising alternatives to traditional inorganic battery materials due to their low-cost, sustainability and structural diversity. The development of carbonyl compounds as energy storage materials is, however, hampered by dissolution as well as by the low electronic conductivity of these materials. Herein a conducting redox polymer concept is employed where the carbonyl group is functionalized onto a conducting polymer. The utilization of a conducting polymer prevents the dissolution and provides electron transport pathways to support the carbonyl group redox reaction. A high potential quinizarin (Qz) is used as capacity-carrying group. It is functionalized onto a thiophene-based trimer unit which is polymerized through a post-deposition polymerization method. In the resulting material, Qz is redox-matched with the conducting polymer backbone and exhibits two reversible 1e/1Li + redox processes at 3.1 and 3.4 V vs. Li + /0 , respectively. Together with a lithium metal anode, a battery cell with an average discharge voltage of 3.3 V, a discharge capacity of 65 mAh/g at 1.5 C and a capacity retention of 74% after 500 cycles is assembled.
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