| 1. |
- Beckmann, Katrin, et al.
(författare)
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On-line mass spectrometry : membrane inlet sampling
- 2009
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Ingår i: Photosynthesis Research. - : Springer Netherlands. - 0166-8595 .- 1573-5079. ; 102:2-3, s. 511-522
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Tidskriftsartikel (refereegranskat)abstract
- Significant insights into plant photosynthesis and respiration have been achieved using membrane inlet mass spectrometry (MIMS) for the analysis of stable isotope distribution of gases. The MIMS approach is based on using a gas permeable membrane to enable the entry of gas molecules into the mass spectrometer source. This is a simple yet durable approach for the analysis of volatile gases, particularly atmospheric gases. The MIMS technique strongly lends itself to the study of reaction flux where isotopic labeling is employed to differentiate two competing processes; i.e., O2 evolution versus O2 uptake reactions from PSII or terminal oxidase/rubisco reactions. Such investigations have been used for in vitro studies of whole leaves and isolated cells. The MIMS approach is also able to follow rates of isotopic exchange, which is useful for obtaining chemical exchange rates. These types of measurements have been employed for oxygen ligand exchange in PSII and to discern reaction rates of the carbonic anhydrase reactions. Recent developments have also engaged MIMS for online isotopic fractionation and for the study of reactions in inorganic systems that are capable of water splitting or H2 generation. The simplicity of the sampling approach coupled to the high sensitivity of modern instrumentation is a reason for the growing applicability of this technique for a range of problems in plant photosynthesis and respiration. This review offers some insights into the sampling approaches and the experiments that have been conducted with MIMS.
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| 2. |
- Conlan, Brendon, et al.
(författare)
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Photo-catalytic oxidation of a di-nuclear manganese centre in an engineered bacterioferritin 'reaction centre'
- 2009
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier. - 0006-3002 .- 1878-2434 .- 0005-2728 .- 1879-2650. ; 1787:9, s. 1112-1121
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthesis involves the conversion of light into chemical energy through a series of electron transfer reactions within membrane-bound pigment/protein complexes. The Photosystem II (PSII) complex in plants, algae and cyanobacteria catalyse the oxidation of water to molecular O(2). The complexity of PSII has thus far limited attempts to chemically replicate its function. Here we introduce a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre. We have used bacterioferritin (BFR) (cytochrome b1) from Escherichia coli as the protein scaffold since it has several, inherently useful design features for engineering light-driven electron transport. Among these are: (i.) a di-iron binding site; (ii.) a potentially redox-active tyrosine residue; and (iii.) the ability to dimerise and form an inter-protein heme binding pocket within electron tunnelling distance of the di-iron binding site. Upon replacing the heme with the photoactive zinc-chlorin e(6) (ZnCe(6)) molecule and the di-iron binding site with two manganese ions, we show that the two Mn ions bind as a weakly coupled di-nuclear Mn(2)(II,II) centre, and that ZnCe(6) binds in stoichiometric amounts of 1:2 with respect to the dimeric form of BFR. Upon illumination the bound ZnCe(6) initiates electron transfer, followed by oxidation of the di-nuclear Mn centre possibly via one of the inherent tyrosine residues in the vicinity of the Mn cluster. The light dependent loss of the Mn(II) EPR signals and the formation of low field parallel mode Mn EPR signals are attributed to the formation of Mn(III) species. The formation of the Mn(III) is concomitant with consumption of oxygen. Our model is the first artificial reaction centre developed for the photo-catalytic oxidation of a di-metal site within a protein matrix which potentially mimics WOC photo-assembly.
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| 3. |
- 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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