| 1. |
- Hughes, Joseph L, et al.
(författare)
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The Native Reaction Centre of Photosystem II: A New Paradigm for P680
- 2004
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Ingår i: Australian Journal of Chemistry. - 0004-9425. ; 57:12, s. 1179-1183
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature spectra of fully active (oxygen-evolving) Photosystem II (PSII) cores prepared from spinach exhibit well developed structure. Spectra of isolated sub-fragments of PSII cores establish that the native reaction centre is better structured and red-shifted compared to the isolated reaction centre. Laser illumination of PSII cores leads to efficient and deep spectral hole-burning. Measurements of homogeneous hole-widths establish excited-state lifetimes in the 40–300 ps range. The high hole-burning efficiency is attributed to charge separation of P680 in native PSII that follows reaction-centre excitation via ‘slow transfer’ states in the inner light-harvesting assemblies CP43 and CP47. The ‘slow transfer’ state in CP47 and that in CP43 can be distinguished in the hole-burning action spectrum and high-resolution hole-burning spectra. An important observation is that 685–700 nm illumination gives rise to efficient P680 charge separation, as established by QA− formation. This leads to a new paradigm for P680. The charge-separating state has surprisingly weak absorption and extends to 700 nm.
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| 2. |
- Peterson Årsköld, Sindra, et al.
(författare)
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Optical Spectra of Synechocystis and Spinach Photosystem II Preparations at 1.7 K: Identification of the D1-Pheophytin Energies and Stark Shifts
- 2003
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 125:43, s. 13063-13074
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Tidskriftsartikel (refereegranskat)abstract
- We report and compare highly resolved, simultaneously recorded absorption and CD spectra of active Photosystem II (PSII) samples in the range 440-750 nm. From an appropriately scaled comparison of spinach membrane fragment (BBY) and PSII core spectra, we show that key features of the core spectrum are quantitatively represented in the BBY data. PSII from the cyanobacterium Synechocystis 6803 display spectral features in the Qy region of comparable width (50-70 cm-1 fwhm) to those seen in plant PSII but the energies of the resolved features are distinctly different. A comparison of spectra taken of PSII poised in the S1QA and S2QA- redox states reveals electrochromic shifts largely attributable to the influence of QA- on PheoD1. This allows accurate determinations of the PheoD1 Qy absorption positions to be at 685.0 nm for spinach cores, 685.8 nm for BBY particles, and 683.0 nm for Synechocystis. These are discussed in terms of earlier reports of the PheoD1 energies in PSII. The Qx transition of PheoD1 undergoes a blue shift upon QA reduction, and we place a lower limit of 80 cm-1 on this shift in plant material. By comparing the magnitude of the Stark shifts of the Qx and Qy bands of PheoD1, the directions of the transition-induced dipole moment changes, x and y, for this functionally important pigment could be determined, assuming normal magnitudes of the 's. Consequently, x and y are determined to be approximately orthogonal to the directions expected for these transitions. Low-fluence illumination experiments at 1.7 K resulted in very efficient formation of QA-. This was accompanied by cyt b559 oxidation in BBYs and carotenoid oxidation in cores. No chlorophyll oxidation was observed. Our data allow us to estimate the quantum efficiency of PSII at this temperature to be of the order 0.1-1. No Stark shift associated with the S1-to-S2 transition of the Mn cluster is evident in our samples. The similarity of Stark data in plants and Synechocystis points to minimal interactions of PheoD1 with nearby chloropyll pigments in active PSII preparations. This appears to be at variance with interpretations of experiments performed with inactive solubilized reaction-center preparations.
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| 3. |
- Prince, Barry J, et al.
(författare)
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Persistent spectral hole burning from oxygen-evolving Photosystem II cores from cyanobacteria and higher plants
- 2004
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 108:1-4, s. 101-105
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Tidskriftsartikel (refereegranskat)abstract
- Persistent spectral hole burning was performed on active Photosystem II (PSII) cores from spinach and Synechocystis 6803, each containing about 32 chl a molecules per core. Hole-burning action spectra are presented. The data appear inconsistent with a mechanism involving non-photochemical hole burning, as has previously been observed in isolated PSII protein-pigment fragments. A photochemical hole-burning mechanism involving charge separation in P680 accounts for the features of the spectra presented.
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| 4. |
- Hughes, Joseph L, et al.
(författare)
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Photoconversion of chlorophylls in higher-plant CP43 characterized by persistent spectral hole burning at 1.7 K.
- 2004
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 108:1-4, s. 131-136
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Tidskriftsartikel (refereegranskat)abstract
- The chorophyll-protein complex CP43 is a proximal-antenna subunit important for excitation energy transfers from peripheral light-harvesting antenna to the Photosystem II (PSII) reaction centre. We report persistent spectral hole burning at 1.7 K in the Qy(0,0) origin and Qy(1,0) vibrational satellite bands of chorophyll a (chl a) in CP43 isolated from higher plants. The isolated CP43 is known to possess two quasi-degenerate 'red' trap states. We find persistent hole burning in the primary trap exhibits a photoconversion property, with a photoproduct located well outside its inhomogeneous distribution. This photoconversion of trap chl a molecules also occurs with non-selective white light illumination. The contribution of the 'red' states to CP43 absorption is discussed.
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| 5. |
- Kritzberg, Emma, et al.
(författare)
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Autochthonous versus allochthonous carbon sources of bacteria: Results from whole-lake C-13 addition experiments
- 2004
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 49:2, s. 588-596
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Tidskriftsartikel (refereegranskat)abstract
- Organic substrates for pelagic bacteria are derived from dissolved organic carbon (DOC) in the water column. DOC is a heterogeneous mixture of molecules, some of which are imported from the watershed (allochthonous DOC) and others that are produced by autotrophs within the system (autochthonous DOC). We examined the importance of autochthonous versus allochthonous DOC in supporting the growth of pelagic bacteria by manipulating the C-13 content of autochthonous sources in a whole-lake experiment. (NaHCO3)-C-13 was added daily to two small forested lakes for a period of 42 d, thereby strongly labeling autochthonous primary production. To obtain bacterial carbon isotopes, bacteria were regrown in vitro in particle-free lake water and in situ in dialysis tubes; little difference was found between the two methods. The contribution of autochthonous versus allochthonous carbon to the bacterial biomass was estimated by applying a two-member mixing model using a C-13 of -28parts per thousand as the allochthonous end member. The autochthonous end member, which varied over time, was estimated indirectly by several approaches. The bacterial biomass consisted of 35-70% allochthonous carbon. This result confirms the often-stated hypothesis that autochthonous carbon alone does not support bacterial production. On the other hand, autochthonous DOC was preferentially utilized relative to terrestrial DOC. On the basis of C-13 measurements, only 13% of the DOC standing stock was of recent autochthonous origin, but it supported 30-65% of bacterial production.
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| 6. |
- Mamedov, Fikret, et al.
(författare)
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Relaxation behaviour of the tyrosine Y-D radical in photosystem II: evidence for strong dipolar interaction with paramagnetic centers in the S-1 and S-2 states
- 2004
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 6:20, s. 4890-4896
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Tidskriftsartikel (refereegranskat)abstract
- Inversion recovery (T-1) and microwave power saturation studies have been performed, between 4 and 25 K, on the EPR signal from the stable tyrosyl radical, Y-D(.), in photosystem II core complex preparations from higher plants. Measurements are reported from the dark stable S-1 and first turnover S-2 states of the photosystem catalytic Mn cluster and in two cryoprotectant regimes; sucrose and ethylene glycol/glycerol. The inversion recovery kinetics show a dominant, non exponential decay component which is well described by a through space dipolar relaxation model, with a weak exponential decay background (similar toan order of magnitude less than the dipolar rate). The dipolar relaxation rate is only modestly temperature dependent and shows no consistent dependence on S state or cryoprotectant. In contrast, the background rate shows a S state dependence, consistent with an interaction between Y-D(.) and the Mn cluster in the multiline S-2 state, over a distance of similar to30 Angstrom. The fraction of centers exhibiting the dipolar relaxation component appears to be temperature dependent, but S state independent and consistent with the presence of a fast relaxing species interacting with Y-D(.). The present results and the possible nature of this interacting species are discussed in comparison with earlier Y-D(.) relaxation studies on photosystem II membrane samples.
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| 7. |
- Peterson Årsköld, Sindra, et al.
(författare)
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Low-temperature spectroscopy of fully active cores. Comparison with CP43, CP47
- 2004
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 108:1-4, s. 97-100
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Tidskriftsartikel (refereegranskat)abstract
- Comparisons of absorption spectra of photosystem II (PSII) core complexes with those of isolated CP43, CP47 and D1/D2/cyt b559 complexes show broadenings and shifts upon disassembly of the PSII core material. Spectra of PSII cores isolated from plants and cyanobacteria reveal marked changes in energies and intensities of the sharp features associated with P680. Low-temperature, illumination-induced electrochromic shifts in PSII cores allow identification of an excitation localized on pheopytin-a (pheo a) in D1. A weak interaction between an exciton component of P680 and the D1 pheo a, both located near 684 nm, is suggested. MCD spectra of 5- and 6-chlorophyll a D1/D2/cytochrome b559 preparations provide links to photoactive pigments in intact PSII cores.
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| 8. |
- Simrén, Magnus, 1966, et al.
(författare)
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Quality of life and illness costs in irritable bowel syndrome.
- 2004
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Ingår i: Digestion. - : S. Karger AG. - 0012-2823 .- 1421-9867. ; 69:4, s. 254-61
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Tidskriftsartikel (refereegranskat)abstract
- Quality of life is reduced in patients with irritable bowel syndrome, and the costs for this disease are substantial to society. During a meeting in London, UK, the IBiS club reviewed the literature on these subjects. Drawbacks and advantages with existing instruments to assess quality of life and costs were discussed and the clinical and scientific relevance of the current knowledge was assessed. A summary from the meeting is presented in this paper.
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| 9. |
- Smith, Paul J, et al.
(författare)
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Magneto-Optical Measurements of the Pigments in Fully Active Photosystem II Core Complexes from Plants
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:6, s. 1981-1989
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Tidskriftsartikel (refereegranskat)abstract
- Preparation of a minimum PSII core complex from spinach is described, containing four Mn per reaction center (RC) and exhibiting high O2 evolving activity [~4000 mol of O2 (mg of chl)-1 h-1]. The complex consists of the CP47 and CP43 chlorophyll binding proteins, the RC D1/D2 pair, the cytochrome b559 subunits, and the Mn-stabilizing psbO (33 kDa) protein, all present in the same stoichiometric amounts found in the parent PSII membranes. Several small subunits are also present. The cyt b559 content is 1.0 per RC in core complexes and PSII membranes. The total chlorophyll content is 32 chl a and <1 chl b per RC, the lowest yet reported for any active PSII preparation. The core complex exhibits the characteristic EPR signals seen in the S2 state of higher plant PSII. A procedure for preparing low-temperature samples of very high optical quality is developed, allowing detailed optical studies in the S1 and S2 states of the system to be made. Optical absorption, CD, and MCD spectra reveal unprecedented detail, including a prominent, well-resolved feature at 683.5 nm (14 630 cm-1) with a weaker partner at 187 cm-1 to higher energy. On the basis of band intensity, CD, and MCD arguments, these features are identified as the exciton split components of P680 in an intact, active reaction center special pair. Comparisons are made with solubilized D1/D2/cyt b559 material and cyanobacterial PSII.
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| 10. |
- Fouts, D. J., et al.
(författare)
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A single-chip false target radar image generator for countering wideband imaging radars
- 2002
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Ingår i: IEEE Journal of Solid-State Circuits. - 0018-9200 .- 1558-173X. ; 37:6, s. 751-759
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the theory, design, implementation, simulation, and testing of an ASIC capable of generating false target radar images for countering wideband synthetic aperture and inverse synthetic aperture imaging radars. The 5.5 x 6.1 mm IC has 81632 transistors, 132 I/O pins, and consumes 0.132 W at 70 MHz from a 3.3-V supply. An introduction to the application and operation of the ASIC in an electronic attack system is also presented. The false target image is fully programmable and the chip is capable of generating images of both small and large targets, even up to the size of an aircraft carrier. This is the first reported use of all-digital technology to generate false target radar images of large targets.
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