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https://www.readbyqxmd.com/read/28534615/origins-of-water-molecules-in-the-photosystem-ii-crystal-structure
#1
Naoki Sakashita, Hiroshi C Watanabe, Takuya Ikeda, Keisuke Saito, Hiroshi Ishikita
The cyanobacterial photosystem II (PSII) crystal structure includes more than 1300 water molecules in each monomer unit; however, their precise roles in water oxidation are unclear. To understand the origins of water molecules in the PSII crystal structure, the accessibility of bulk water molecules to channel inner spaces in PSII was investigated using the water-removed PSII structure and molecular dynamics (MD) simulations. The inner space of the channel that proceeds toward the D1-Glu65/D2-Glu312 pair (E65/E312 channel) was entirely filled with water molecules from the bulk region...
May 23, 2017: Biochemistry
https://www.readbyqxmd.com/read/28531219/pyldm-an-open-source-package-for-lifetime-density-analysis-of-time-resolved-spectroscopic-data
#2
Gabriel F Dorlhiac, Clyde Fare, Jasper J van Thor
Ultrafast spectroscopy offers temporal resolution for probing processes in the femto- and picosecond regimes. This has allowed for investigation of energy and charge transfer in numerous photoactive compounds and complexes. However, analysis of the resultant data can be complicated, particularly in more complex biological systems, such as photosystems. Historically, the dual approach of global analysis and target modelling has been used to elucidate kinetic descriptions of the system, and the identity of transient species respectively...
May 22, 2017: PLoS Computational Biology
https://www.readbyqxmd.com/read/28530393/structural-factors-that-alter-the-redox-potential-of-quinones-in-cyanobacterial-and-plant-photosystem-i
#3
Keisuke Kawashima, Hiroshi Ishikita
Using the cyanobacterial and plant photosystem I (PSI) crystal structures and by considering the protonation states of all titratable residues, redox potentials (Em) of the two phylloquinones--A1A and A1B--were calculated. The calculated Em values were Em(A1A) = -773 mV and Em(A1B) = -818 mV for the plant PSI structure and Em(A1A) = -612 mV and Em(A1B) = -719 mV for the cyanobacterial PSI structure. Our analysis of the PSI crystal structures suggested that the side-chain orientations of Lys-B542 and Gln-B678 in the cyanobacterial crystal structure differ from these side-chain orientations in the plant crystal structure...
May 22, 2017: Biochemistry
https://www.readbyqxmd.com/read/28526981/rubisco-mutants-of-chlamydomonas-reinhardtii-display-divergent-photosynthetic-parameters-and-lipid-allocation
#4
M G Esquível, A R Matos, J Marques Silva
Photosynthesis and lipid allocation were investigated in Rubisco small subunit mutants of the microalga Chlamydomonas reinhardtii. Comparative analyses were undertaken with cells grown photoheterotrophically under sulphur-replete or sulphur-depleted conditions. The Y67A Rubisco mutant, which has previously demonstrated a pronounced reduction in Rubisco levels and higher hydrogen production rates than the wild type, also shows the following divergences in photosynthetic phenotype and lipid allocation: (i) low Fv/Fm (maximum photochemical efficiency), (ii) low effective quantum yield of photosystem II (ΦPSII), (iii) low effectiveness at protection against high light intensities, (iv) a higher level of total lipids per pigment and (v) changes in the relative proportions of different fatty acids, with a marked decrease in unsaturated fatty acids (FAs)...
May 19, 2017: Applied Microbiology and Biotechnology
https://www.readbyqxmd.com/read/28526061/photosynthesis-at-the-far-red-region-of-the-spectrum-in-acaryochloris-marina
#5
REVIEW
Syed Lal Badshah, Yahia Mabkhot, Salim S Al-Showiman
Acaryochloris marina is an oxygenic cyanobacterium that utilizes far-red light for photosynthesis. It has an expanded genome, which helps in its adaptability to the environment, where it can survive on low energy photons. Its major light absorbing pigment is chlorophyll d and it has α-carotene as a major carotenoid. Light harvesting antenna includes the external phycobilin binding proteins, which are hexameric rods made of phycocyanin and allophycocyanins, while the small integral membrane bound chlorophyll binding proteins are also present...
May 19, 2017: Biological Research
https://www.readbyqxmd.com/read/28524662/x-ray-emission-spectroscopy-of-biomimetic-mn-coordination-complexes
#6
Scott C Jensen, Katherine M Davis, Brendan T Sullivan, Daniel A Hartzler, Gerald T Seidler, Diego M Casa, Elina Kasman, Hannah E Colmer, Allyssa A Massie, Timothy A Jackson, Yulia N Pushkar
Understanding the function of Mn ions in biological and chemical redox catalysis requires precise knowledge of their electronic structure. X-ray emission spectroscopy (XES) is an emerging technique with growing application to biological and biomimetic systems. Here, we report an improved, cost-effective spec-trometer used to analyze two biomimetic coordination compounds: [MnIV(OH)2(Me2EBC)]2+ and [MnIV(O)(OH)(Me2EBC)]+, the second of which contains a key MnIV=O structural fragment. Despite having the same formal oxidation state (MnIV) and tetradentate ligands, XES spectra from these two compounds demonstrate different electronic structures...
May 19, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28523605/erratum-to-connectivity-between-electron-transport-complexes-and-modulation-of-photosystem-ii-activity-in-chloroplasts
#7
Alexander N Tikhonov, Alexey V Vershubskii
No abstract text is available yet for this article.
May 18, 2017: Photosynthesis Research
https://www.readbyqxmd.com/read/28522455/psa3-a-protein-on-the-stromal-face-of-the-thylakoid-membrane-promotes-photosystem-i-accumulation-in-cooperation-with-the-assembly-factor-pyg7
#8
Jie Shen, Rosalind Williams-Carrier, Alice Barkan
Photosystem I (PSI) is a large protein-pigment complex located in the thylakoid membrane in cyanobacteria, plants, and algae. Although the structure and components of PSI are well characterized, mechanisms that orchestrate its assembly are poorly understood. In this study, we discovered a novel nucleus-encoded protein, Photosystem I Assembly 3 (PSA3), that is required for PSI accumulation. PSA3 is conserved among green photosynthetic eukaryotes but is lacking in cyanobacteria. Mutations in the psa3 gene cause the specific loss of PSI in Arabidopsis and maize...
May 18, 2017: Plant Physiology
https://www.readbyqxmd.com/read/28515738/chloroplast-atp-synthase-modulation-of-the-thylakoid-proton-motive-force-implications-for-photosystem-i-and-photosystem-ii-photoprotection
#9
Atsuko Kanazawa, Elisabeth Ostendorf, Kaori Kohzuma, Donghee Hoh, Deserah D Strand, Mio Sato-Cruz, Linda Savage, Jeffrey A Cruz, Nicholas Fisher, John E Froehlich, David M Kramer
In wild type plants, decreasing CO2 lowers the activity of the chloroplast ATP synthase, slowing proton efflux from the thylakoid lumen resulting in buildup of thylakoid proton motive force (pmf). The resulting acidification of the lumen regulates both light harvesting, via the qE mechanism, and photosynthetic electron transfer through the cytochrome b6f complex. Here, we show that the cfq mutant of Arabidopsis, harboring single point mutation in its γ-subunit of the chloroplast ATP synthase, increases the specific activity of the ATP synthase and disables its down-regulation under low CO2...
2017: Frontiers in Plant Science
https://www.readbyqxmd.com/read/28508474/interrogation-of-a-ps1-based-photocathode-by-means-of-scanning-photoelectrochemical-microscopy
#10
Fangyuan Zhao, Nicolas Plumeré, Marc M Nowaczyk, Adrian Ruff, Wolfgang Schuhmann, Felipe Conzuelo
In the development of photosystem-based energy conversion devices, the in-depth understanding of electron transfer processes involved in photocurrent generation and possible charge recombination is essential as a basis for the development of photo-bioelectrochemical architectures with increased efficiency. The evaluation of a bio-photocathode based on photosystem 1 (PS1) integrated within a redox hydrogel by means of scanning photoelectrochemical microscopy (SPECM) is reported. The redox polymer acts as a conducting matrix for the transfer of electrons from the electrode surface to the photo-oxidized P700 centers within PS1, while methyl viologen is used as charge carrier for the collection of electrons at the reduced FB site of PS1...
May 16, 2017: Small
https://www.readbyqxmd.com/read/28507666/in-situ-observation-of-reactive-oxygen-species-forming-on-oxygen-evolving-iridium-surfaces
#11
Verena Pfeifer, Travis E Jones, Juan J Velasco Vélez, Rosa Arrigo, Simone Piccinin, Michael Hävecker, Axel Knop-Gericke, Robert Schlögl
Water splitting performed in acidic media relies on the exceptional performance of iridium-based materials to catalyze the oxygen evolution reaction (OER). In the present work, we use in situ X-ray photoemission and absorption spectroscopy to resolve the long-standing debate about surface species present in iridium-based catalysts during the OER. We find that the surface of an initially metallic iridium model electrode converts into a mixed-valent, conductive iridium oxide matrix during the OER, which contains O(II-) and electrophilic O(I-) species...
March 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28504210/arachidonic-acid-is-important-for-efficient-use-of-light-by-the-microalga-lobosphaera-incisa-under-chilling-stress
#12
Boris Zorin, Dipasmita Pal-Nath, Alexander Lukyanov, Sviatlana Smolskaya, Sofiya Kolusheva, Shoshana Didi-Cohen, Sammy Boussiba, Zvi Cohen, Inna Khozin-Goldberg, Alexei Solovchenko
The oleaginous microalga Lobosphaera incisa (Trebouxiophyceae, Chlorophyta) contains arachidonic acid (ARA, 20:4 n-6) in all membrane glycerolipids and in the storage lipid triacylglycerol. The optimal growth temperature of the wild-type (WT) strain is 25°C; chilling temperatures (≤15°C) slow its growth. This effect is more pronounced in the delta-5-desaturase ARA-deficient mutant P127, in which ARA is replaced with dihomo-γ-linolenic acid (DGLA, 20:3 n-6). In nutrient-replete cells grown at 25°C, the major chloroplast lipid monogalactosylglycerol (MGDG) were dominated by C18/C16 species in both strains...
May 11, 2017: Biochimica et Biophysica Acta
https://www.readbyqxmd.com/read/28500711/quantum-chemical-spin-densities-for-radical-cations-of-photosynthetic-pigment-models
#13
Denis G Artiukhin, Christopher J Stein, Markus Reiher, Johannes Neugebauer
The spin densities of radical cations of magnesium porphyrin, magnesium chlorine and a truncated chlorophyll a model are calculated with density-functional theory and multiconfigurational quantum chemical methods. The latter serve as a reference for approximate density-functional theory which yields spin densities that may suffer from the self-interaction error. We carried out complete active space self-consistent field calculations with increasing active orbital spaces to systematically converge qualitatively correct spin densities...
May 2017: Photochemistry and Photobiology
https://www.readbyqxmd.com/read/28500680/rapid-detoxification-via-glutathione-s-transferase-gst-conjugation-confers-high-level-of-atrazine-resistance-in-palmer-amaranth-amaranthus-palmeri
#14
Sridevi Nakka, Amar S Godar, Curtis R Thompson, Dallas E Peterson, Mithila Jugulam
BACKGROUND: Palmer amaranth (Amaranthus palmeri) is an economically troublesome, aggressive and damaging weed that has evolved resistance to six herbicide modes of action (MOA) including photosystem II (PS II)-inhibitors, such as atrazine. The objective of this study was to investigate the mechanism and inheritance of atrazine resistance in Palmer amaranth. RESULTS: A population of Palmer amaranth from Kansas (KSR) had a high level (160-198 fold more; SE ± 21-26) of resistance to atrazine compared to the two known susceptible populations MSS and KSS, from Mississippi and KS, respectively...
May 13, 2017: Pest Management Science
https://www.readbyqxmd.com/read/28500267/impaired-mitochondrial-transcription-termination-disrupts-the-stromal-redox-poise-in-chlamydomonas
#15
Andreas Uhmeyer, Matteo Ballottari, Michela Cecchin, Lutz Wobbe
In photosynthetic eukaryotes, the metabolite exchange between chloroplast and mitochondria ensures efficient photosynthesis under saturating light conditions. The C. reinhardtii mutant stm6 is devoid of the mitochondrial transcription termination factor (mTERF) MOC1 and aberrantly expresses the mitochondrial genome, resulting in enhanced photosynthetic hydrogen production and diminished light tolerance. We analyzed the modulation of mitochondrial and chlororespiration during the acclimation of stm6 and the MOC1-complemented strain to excess light...
May 12, 2017: Plant Physiology
https://www.readbyqxmd.com/read/28499880/photoprotection-strategies-of-the-alga-nannochloropsis-gaditana
#16
Volha U Chukhutsina, Rikard Fristedt, Tomas Morosinotto, Roberta Croce
Nannochloropsis spp. are algae with high potential for biotechnological applications due to their capacity to accumulate lipids. However, little is known about their photosynthetic apparatus and acclimation/photoprotective strategies. In this work, we studied the mechanisms of non-photochemical quenching (NPQ), the fast response to high light stress, in Nannochloropsis gaditana by "locking" the cells in six different states during quenching activation and relaxation. Combining biochemical analysis with time-resolved fluorescence spectroscopy, we correlated each NPQ state with the presence of two well-known NPQ components: de-epoxidized xanthophylls and stress-related antenna proteins (LHCXs)...
May 9, 2017: Biochimica et Biophysica Acta
https://www.readbyqxmd.com/read/28497947/energy-transfer-kinetics-in-photosynthesis-as-an-inspiration-for-improving-organic-solar-cells
#17
Collins Nganou, Gerhard Lackner, Bezu Teschome, M Jamal Deen, Noam Adir, David Pouhe, Doru C Lupascu, Martin Mkandawire
Clues to designing highly efficient organic solar cells may lie in understanding the architecture of light-harvesting systems and exciton energy transfer (EET) processes in very efficient photosynthetic organisms. Here, we compare the kinetics of excitation energy tunnelling from the intact phycobilisome (PBS) light-harvesting antenna system to the reaction center in photosystem II in intact cells of the cyanobacterium Acaryochloris marina with the charge transfer after conversion of photons into photocurrent in vertically aligned carbon nanotube (va-CNT) organic solar cells with poly(3-hexyl)thiophene (P3HT) as the pigment...
May 22, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28497193/evaluation-of-new-cu-ii-complexes-as-a-novel-class-of-inhibitors-against-plant-carbonic-anhydrase-glutathione-reductase-and-photosynthetic-activity-in-photosystem-ii
#18
Margarita V Rodionova, Sergei K Zharmukhamedov, Mehmet Sayım Karacan, Kubra Begum Venedik, Alexandr V Shitov, Turgay Tunç, Serhat Mamaş, Vladimir D Kreslavski, Nurcan Karacan, Vyacheslav V Klimov, Suleyman I Allakhverdiev
Increasing inefficiency of production of important agricultural plants raises one of the biggest problems in the modern world. Herbicide application is still the best method of weed management. Traditional herbicides blocking only one of the plant metabolic pathways is ineffective due to the rapid growth of herbicide-resistant weeds. The synthesis of novel compounds effectively suppressing several metabolic processes, and therefore achieving the synergism effect would serve as the alternative approach to weed problem...
May 11, 2017: Photosynthesis Research
https://www.readbyqxmd.com/read/28494358/herbicide-effects-on-the-growth-and-photosynthetic-efficiency-of-cassiopea-maremetens
#19
David J Rowen, Michelle A Templeman, Michael J Kingsford
Herbicides from agricultural run-off have been measured in coastal systems of the Great Barrier Reef over many years. Non-target herbicide exposure, especially photosystem II herbicides has the potential to affect seagrasses and other marine species. The symbiotic benthic jellyfish Cassiopea maremetens is present in tropical/sub-tropical estuarine and marine environments. Jellyfish (n = 8 per treatment) were exposed to four separate concentrations of agricultural formulations of diuron or hexazinone to determine their sensitivity and potential for recovery to pulsed herbicide exposure...
May 1, 2017: Chemosphere
https://www.readbyqxmd.com/read/28489091/role-of-missing-carotenoid-in-reducing-the-fluorescence-of-single-monomeric-photosystem-ii-core-complexes
#20
Sepideh Skandary, Frank Müh, Imran Ashraf, Mohamed Ibrahim, Michael Metzger, Athina Zouni, Alfred J Meixner, Marc Brecht
The fluorescence of monomeric photosystem II core complexes (mPSIIcc) of the cyanobacterium Thermosynechococcus elongatus, originating from redissolved crystals, is investigated by using single-molecule spectroscopy (SMS) at 1.6 K. The emission spectra of individual mPSIIcc are dominated by sharp zero-phonon lines, showing the existence of different emitters compatible with the F685, F689, and F695 bands reported formerly. The intensity of F695 is reduced in single mPSIIcc as compared to single PSIIcc-dimers (dPSIIcc)...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
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