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Journal articles on the topic 'Photosystem 1'

Author: Grafiati

Published: 4 June 2021

Last updated: 1 February 2022

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1

Barbato, R., G. Friso, F. Rigoni, F. Dalla Vecchia, and G. M. Giacometti. "Structural changes and lateral redistribution of photosystem II during donor side photoinhibition of thylakoids." Journal of Cell Biology 119, no. 2 (October 15, 1992): 325–35. http://dx.doi.org/10.1083/jcb.119.2.325.

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The structural and topological stability of thylakoid components under photoinhibitory conditions (4,500 microE.m-2.s-1 white light) was studied on Mn depleted thylakoids isolated from spinach leaves. After various exposures to photoinhibitory light, the chlorophyll-protein complexes of both photosystems I and II were separated by sucrose gradient centrifugation and analysed by Western blotting, using a set of polyclonals raised against various apoproteins of the photosynthetic apparatus. A series of events occurring during donor side photoinhibition are described for photosystem II, including: (a) lowering of the oligomerization state of the photosystem II core; (b) cleavage of 32-kD protein D1 at specific sites; (c) dissociation of chlorophyll-protein CP43 from the photosystem II core; and (d) migration of damaged photosystem II components from the grana to the stroma lamellae. A tentative scheme for the succession of these events is illustrated. Some effects of photoinhibition on photosystem I are also reported involving dissociation of antenna chlorophyll-proteins LHCI from the photosystem I reaction center.

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2

Bader, Klaus P., and Susanne Höper. "Stimulatory Effects of an Ammonium Salt Biocide on Photosynthetic Electron Transport Reactions." Zeitschrift für Naturforschung C 49, no. 1-2 (February 1, 1994): 87–94. http://dx.doi.org/10.1515/znc-1994-1-214.

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Alkylbenzyldimethylammonium chloride (ABDAC, zephirol) has been shown to improve the functioning of the photosynthetic apparatus of the filamentous cyanobacterium Oscillatoria chalybea (Bader, K. P. (1989) Biochim. Biophys. Acta 975, 399-402). This biocide exerts stimulatory effects on various electron transport reactions in Oscillatoria chalybea and chloroplasts from higher plants. By means of oxygen evolution measurements and of repetitive flash-induced absorption spectroscopy we were able to demonstrate an impact of the drug on the major complexes of photosynthetic membranes, i.e. the water splitting complex, photosystem II and photosystem I. Both, P820- and X320-absorption change signals were enhanced by the addition of ABDAC. Along with the quantitative analysis we investigated the relaxation kinetics of the signals and observed a substantial stabilization of the oxidized states of the respective redox components in the presence of the ammonium salt. Under appropriate conditions the relaxation kinetics of the absorption signals were significantly slowed down. ABDAC also affects photosystem I in Oscillatoria chalybea, but only under conditions, where a donor/acceptor system i.e. an isolated photosystem I reaction with photosystem II being disconnected was measured. Electron transport through the whole chain i.e. with water as the electron donor yielded no effect of the quaternary ammonium salt. It is suggested that this is due to an extremely bad linkage between the two photosystem, each of which, however, shows good reaction rates, when separately measured. The described interactions of the biocide with photosynthetic membranes are not restricted to Oscillatoria chalybea but are also observed with higher plant chloroplasts. In these systems, ABDAC enhances X320- and P700-signals to a comparable extent. In this case the P700-signal is stimulated in assays with electrons which are furnished from water which hints at good coupling between the two photosystems in our tobacco chloroplast preparations.

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3

Oettmeier, Walter, Klaus Masson, and Jörg Höhfeld. "[125I]Azido-Ioxynil Labels Val249 of the Photosystem II D -1 Reaction Center Protein." Zeitschrift für Naturforschung C 44, no. 5-6 (June 1, 1989): 444–49. http://dx.doi.org/10.1515/znc-1989-5-617.

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Abstract Azido-ioxynil (3,5-diiodo-2-azido-4-hydroxy-benzonitrile) is a potent photosystem II inhibitor (pI50-value 7.38) and as effective as the parent compound ioxynil itself. [125I]azido-ioxynil exhibits specific binding to isolated thylakoids with a binding constant Kb = 7.14. Upon UV -illumination it binds covalently to thylakoids or photosystem II particles. It labels predominantly the 32 kDa D-1 photosystem II reaction center protein . A 41 kDa protein is only tagged in trace amounts. After proteolytic treatment of labeled D -1 protein with Staphylococcus aureaus V8 -protease two major and two minor fragments are obtained. Automated gas phase sequencing of a 7 kDa cleavage peptide revealed that Val249 is the primary target of azido-ioxynil binding. Compared to urea type herbicides, this places the ioxynil binding site in a different environment of the D -1 photosystem II protein.

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4

Sabat, S. C., V. Vijayavergiya, B. C. Tripathy, and Prasanna Mohanty. "Inhibitory Effect of Crown Compound on Photoelectron Transport Activity of Beet Spinach Thylakoid Membranes." Zeitschrift für Naturforschung C 46, no. 1-2 (February 1, 1991): 87–92. http://dx.doi.org/10.1515/znc-1991-1-214.

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Abstract The effect of K-picrate-18-crown-6 (crown) on the photoelectron transport activity of beet spinach thylakoid membranes was investigated. Addition of micromolar concentration of crown to thylakoid preparation inhibited p-benzoquinone, chloride-indophenol, methyl viologen supported Hill activities maximally by 75 per cent in a concentration dependent manner. However, the photosystem I catalyzed reaction remained insensitive to crown suggesting that crown specifically inhibits photosystem II electron transport. Addition of exogenous electron donors like hydroxylamine or diphenylcarbazide failed to restore the crown induced inhibition of photosystem II electron transport and lowering of steady state chlorophyll a fluorescence yield. These observations suggest that crown also inhibits photosystem II catalyzed electron transport after the donation sites of these exogenous donors. Washing of the crown pre-treated thylakoids with isolation buffer, relieved the crown inhibited electron transport activity, indicating that this inhibition is reversible. Furthermore, in hydroxylamine washed thylakoids which are devoid of O2 evolution capacity, the hydroxylamine induced increase in chlorophyll a fluorescence of variable yield was quenched by the addition of crown. These observations suggest that crown affects the oxygen evolution and inhibits at a site close to photosystem II reaction centres.

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5

Xu, C., and J. J. S. van Rensen. "On the Requirement of Bound Bicarbonate for Photosystem II Activity." Zeitschrift für Naturforschung C 52, no. 1-2 (February 1, 1997): 24–32. http://dx.doi.org/10.1515/znc-1997-1-205.

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Abstract In photosystem II of plants and cyanobacteria, but not in reaction centers of anoxygenic photosynthetic bacteria, formate is known to inhibit electron flow which is reversed fully upon bicarbonate addition. At issue has been an old controversy whether this effect is on the acceptor or the donor side of photosystem II (PS II). We present here data on chloroplast thylakoids for donor side effects, that is accompanied by acceptor side effects, from measurements on chlorophyll a fluorescence yield changes after light flashes 1-6. Further, sensitive differential infrared gas analyser measurements show that bicarbonate is indeed bound in both maize and pea thylakoid suspensions depleted of CO2 without any inhibitor; here, high rates of electron flow are associated with the presence of a maximum of 0.8 to 1.25 (corrected for residual activity) CO2 per photosystem II reaction center. It is suggested that bicarbonate bound to the acceptor side is required for photosystem II activity , both on the acceptor and the donor sides in the same experiment and in the same sample.

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6

Symons, Marc, Shmuel Malkin, and Daniel L. Farkas. "Electric-field-induced luminescence emission spectra of Photosystem I and Photosystem II from chloroplasts." Biochimica et Biophysica Acta (BBA) - Bioenergetics 894, no. 3 (December 1987): 578–82. http://dx.doi.org/10.1016/0005-2728(87)90138-1.

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7

Ruff, Mathias, and Elfriede K. Pistorius. "Isolation and Partial Characterization of a Manganese and Chloride Binding Protein Present in Highly Purified Photosystem II Complexes of the Thermophilic Cyanobacterium Synechococcus sp.: The Protein Being Detected by Its L -Arginine Metabolizing Activity." Zeitschrift für Naturforschung C 49, no. 1-2 (February 1, 1994): 95–107. http://dx.doi.org/10.1515/znc-1994-1-215.

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Photosystem II complexes were solubilized with the detergent sulfobetaine 12 from thylakoid membranes of the thermophilic cyanobacterium Synechococcus sp. and purified by two sucrose gradient centrifugations and by chromatography on a Mono Q column. In such photosystem II complexes having a photosynthetic O2, evolving activity of 2938 μmol O2 evolved/mg chlorophyll x h, an ʟ-arginine metabolizing activity leading to ornithine and urea as major products, could be shown to be present. Besides ornithine and urea, a product (or products) of yet unknown structure is formed in addition - especially under aerobic conditions. This activity remained associated with photosystem II complexes even after substantial additional treatments to remove loosely bound proteins. On chlorophyll basis the maximal activity obtained under optimal assay conditions corresponded to 94 μmol ornithine formed/mg chlorophyll x h. This PS II associated, ʟ-arginine metabolizing enzyme was isolated (utilizing a manganese charged chelating Sepharose 6 B column) and partially characterized. It could be shown that this enzyme requires manganese and chloride for its ʟ-arginine metabolizing activity and that manganese becomes totally lost during purification indicating that manganese is bound to a fairly exposed site on the protein. Since it is rather unlikely that two different manganese and chloride binding proteins are present in such highly purified photosystem II complexes, the possibility of this protein being the water oxidizing enzyme will be discussed. Whether the manganese and chloride requiring ʟ-arginine metabolizing activity of this protein which provided a suitable assay for its isolation from photosystem II complexes, has any physiological significance, can not be answered at the present time.

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8

Allakhverdieva, Y. M., M. D. Mamedov, N. Ferimazova, G. C. Papageorgiou, and R. A. Gasanov. "Glycinebetaine Stabilizes Photosystem 1 and Photosystem 2 Electron Transport in Spinach Thylakoid Membranes Against Heat Inactivation." Photosynthetica 37, no. 3 (November 1, 1999): 423–32. http://dx.doi.org/10.1023/a:1007159827344.

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9

Chow, Wah Soon, Hae-Youn Lee, Jie He, Luke Hendrickson, Young-Nam Hong, and Shizue Matsubara. "Photoinactivation of Photosystem II in leaves." Photosynthesis Research 84, no. 1-3 (June 2005): 35–41. http://dx.doi.org/10.1007/s11120-005-0410-1.

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10

Roose, Johnna L., Kimberly M. Wegener, and Himadri B. Pakrasi. "The extrinsic proteins of Photosystem II." Photosynthesis Research 92, no. 3 (January 3, 2007): 369–87. http://dx.doi.org/10.1007/s11120-006-9117-1.

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11

Thiemann, Jutta, and Wolfgang Barz. "Photoautotrophic Chenopodium rubrum Cell Suspension Cultures Resistant against Photosynthesis-Inhibiting Herbicides II. Physiological and Biochemical Properties." Zeitschrift für Naturforschung C 49, no. 11-12 (December 1, 1994): 791–801. http://dx.doi.org/10.1515/znc-1994-11-1215.

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Eight photoautotrophic cell cultures of Chenopodium rubrum, which are resistant against the photosystem II inhibitor metribuzin, were characterized for their growth parameters, chlorophyll content and photosynthetic capacity. Herbicide resistance of the eight lines results from different mutations in the D 1 protein of photosystem II, which is the target for different photosystem II inhibitors. In the presence of 10-5 ᴍ metribuzin the eight lines showed substantial growth reduction depending on the degree of resistance, and this effect is explained by a reduced electron transport in photosystem II. The impaired photosynthetic capacity of the green cells in the presence of high metribuzin concentrations, leads to compensation effects similar to shade accommodation of plants. Adaptation includes an increase of the chlorophyll content, a decrease of the chlorophyll a/b ratios as well as an increase of thylakoid stacking and cell number per unit fresh weight. In the absence of the herbicide photosynthetic electron transport is not impaired, as indicated by measurements of electron transfer rates in photosystem II and flash-induced reduction kinetics of P-700+. In summary the alterations of the D 1 protein of the eight cell lines do not result in a reduced electron transport in photosystem II.

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12

Canonico, Myriam, Grzegorz Konert, Aurélie Crepin, Barbora Šedivá, and Radek Kaňa. "Gradual Response of Cyanobacterial Thylakoids to Acute High-Light Stress—Importance of Carotenoid Accumulation." Cells 10, no. 8 (July 28, 2021): 1916. http://dx.doi.org/10.3390/cells10081916.

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Light plays an essential role in photosynthesis; however, its excess can cause damage to cellular components. Photosynthetic organisms thus developed a set of photoprotective mechanisms (e.g., non-photochemical quenching, photoinhibition) that can be studied by a classic biochemical and biophysical methods in cell suspension. Here, we combined these bulk methods with single-cell identification of microdomains in thylakoid membrane during high-light (HL) stress. We used Synechocystis sp. PCC 6803 cells with YFP tagged photosystem I. The single-cell data pointed to a three-phase response of cells to acute HL stress. We defined: (1) fast response phase (0–30 min), (2) intermediate phase (30–120 min), and (3) slow acclimation phase (120–360 min). During the first phase, cyanobacterial cells activated photoprotective mechanisms such as photoinhibition and non-photochemical quenching. Later on (during the second phase), we temporarily observed functional decoupling of phycobilisomes and sustained monomerization of photosystem II dimer. Simultaneously, cells also initiated accumulation of carotenoids, especially ɣ–carotene, the main precursor of all carotenoids. In the last phase, in addition to ɣ-carotene, we also observed accumulation of myxoxanthophyll and more even spatial distribution of photosystems and phycobilisomes between microdomains. We suggest that the overall carotenoid increase during HL stress could be involved either in the direct photoprotection (e.g., in ROS scavenging) and/or could play an additional role in maintaining optimal distribution of photosystems in thylakoid membrane to attain efficient photoprotection.

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13

Nitsch, Christian, Silvia E. Braslavsky, and Günther H. Schatz. "Laser-induced optoacoustic calorimetry of primary processes in isolated Photosystem I and Photosystem II particles." Biochimica et Biophysica Acta (BBA) - Bioenergetics 934, no. 2 (July 1988): 201–12. http://dx.doi.org/10.1016/0005-2728(88)90183-1.

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14

Karapetyan, Navassard V., Ute Windhövel, Alfred R. Holzwarth, and Peter Böger. "Physiological Significance of Overproduced Carotenoids in Transformants of the Cyanobacterium Synechococcus PCC7942." Zeitschrift für Naturforschung C 54, no. 3-4 (April 1, 1999): 191–98. http://dx.doi.org/10.1515/znc-1999-3-409.

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Abstract The functional location of carotenoids in the photosynthetic apparatus of -crtB and -pys transformants of the cyanobacterium Synechococcus PCC7942 was studied and compared with a control strain -pFP 1-3. These transformants overproduce carotenoids due to the insertion of an additional foreign phytoene synthase gene. A higher carotenoid content was found for -crtB and -pys transformants both in whole cells and isolated membranes; the -crtB transformant was also enriched with chlorophyll. 77-K fluorescence emission and excitation spectra of the phycobilin-free membranes were examined for a possible location of overproduced carotenoids in pigment-protein complexes in situ. A similar ratio of the amplitudes of fluorescence bands at 716 and 695 nm emitted by photosystems I and II, found for the three strains, indicates that the stoichiometry between photosystems of the transformants was not changed. Overproduced carotenoids are not located in the core antenna of photosys tem I, since 77-K fluorescence excitation spectra for photosystem I of isolated membranes from the studied strains do not differ in the region of carotenoid absorption. When illuminated with light of the same intensity but different quality, absorbed preferentially by either carotenoids, chlorophylls or phycobilins, respectively, oxygen evolution was found always higher in the transformants -crtB and -pys than in -pFP 1-3 control cells. Identical kinetics of fluorescence induction of all strains under carotenoid excitation did not reveal a higher activity of photosystem II in cells enriched with carotenoids. It is suggested that overproduced carotenoids of the transformants are not involved in photosynthetic light-harvesting; rather they may serve to protect the cells and its membranes against photodestruction.

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15

Makewicz, A., A. Radunz, and G. H. Schmid. "Immunological Evidence for the Binding of β-Carotene and Xanthophylls onto Peptides of Photosystem I from Nicotiana tabacum." Zeitschrift für Naturforschung C 49, no. 7-8 (August 1, 1994): 427–38. http://dx.doi.org/10.1515/znc-1994-7-807.

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Photosystem I preparations were obtained from wild type tobacco Nicotiana tabacum var. John William’s Broadleaf (JWB) and from the two chlorophyll-deficient mutants N. tabacum Su/su and N. tabacum Su/su var. Aurea. The preparations were characterized with respect to the chlorophyll a/b ratio, their photosynthetic activity and their absorption spectroscopic properties. Peptides from these preparations were analyzed by SDS polyacrylamide gel electrophoresis and transferred for the detection of bound carotenoids according to the Western blot procedure to nitrocellulose or Immobilon membranes. The PS I preparation from the wild type JWB consisted of the core and the LHCP complex. The core complex contains the two core peptides with the same apparent MW of 66 kDa and several peptides with the lesser molecular masses of 22, 20, 19, 17, 16, 10 and 9 kDa. The light-harvesting protein complex consists of 4 subunits with the molecular masses 28, 26, 25 and 24 kDa. The PS I preparations of the yellow-green mutant Su/su and of the Aurea mutant Su/su var. Aurea contain as impurity traces of the D1 and D2 core peptides of photosystem II and also traces of the chlorophyll-binding photosystem II peptides with the molecular masses 42 and 47 kDa. The peptides of the photosystem I preparation were characterized by specific photosystem I antisera: An antiserum to the photosystem I complex reacts in the Western blot only with the homologous peptides of photosystem I. In comparative analyses with photosystem II preparations this antiserum (directed to photosystem I) reacts, as expected, only with the peptides of the light-harvesting complex. An antiserum to the CP 1 core peptides reacts only with the 66 kDa peptides of photosystem I and gives no cross reaction with heterodimer forms of the D1/D2 core peptides of photosystem II. In the Western blot procedure by means of polyclonal monospecific antisera to carotenoids it was demonstrated that β-carotene is bound in high concentration onto the core peptides CP 1 and to a lesser extent onto the two larger subunits of the LHCP complex, exhibiting the molecular masses of 28 and 26 kDa. Neoxanthin is bound onto the same peptides. In contrast to this, lutein was only identified on the core peptides CP 1 and violaxanthin only on the larger subunits of the LHCP complex. As the carotenoids are labelled with antibodies, even after SDS treatment in the electrophoresis, it is assumed, that the carotenoids are covalently bound via the ionon ring to the respective peptide

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16

Kloos, Ralf, Edward Stevens, and Walter Oettmeier. "Complete Sequence of One Copy of the psbA Gene from the Thermophilic Cyanobacterium Synechococcus elongatus." Zeitschrift für Naturforschung C 48, no. 9-10 (October 1, 1993): 799–802. http://dx.doi.org/10.1515/znc-1993-9-1019.

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Abstract One copy of the psbA. gene which codes for the photosystem II reaction center D-1 protein from the thermophilic cyanobacterium Synechococcus elongatus has been sequenced. It is feasible that a disulfide bridge between D-1 Cys212 and D-2 Cys2I2 is reponsible for the thermo stability of the photosystem II reaction center from Synechococcus elongatus.

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17

Figueredo, Cleber Cunha, Alessandra Giani, and José Pires Lemos Filho. "Photosynthetic capacity of three phytoplanktonic species measured by a pulse amplitude fluorometric method." Brazilian Journal of Plant Physiology 21, no. 3 (2009): 167–74. http://dx.doi.org/10.1590/s1677-04202009000300001.

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During photosynthesis, absorbed energy that is not used in photochemical reactions dissipates as fluorescence. Fluorescence provides important information on the physiological conditions of the studied organisms and its measurement is widely used by plant physiologists and can be valuable in phytoplankton studies. We describe a method adapting a plant fluorometric equipment to measure the photosynthetic capacity of microalgae. Unialgal cultures of three planktonic chlorophytes were exposed to 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II, at concentrations of 0.1, 1.0 and 10.0 µmol.L-1. Estimates were made of photosynthetic parameters, including operational and potential photosystem II quantum yield and electron transport rate between photosystems, using algal cells concentrated on glass-fiber filters. The technique allowed reliable measurements of fluorescence, and detection of distinct levels of inhibition. Physiological or morphological characteristics of the selected species might provide an explanation for the observed results: differences on the surface/volume ratio of the cells and colony morphology, for example, were associated with contrasting resistance to the toxicant. To characterize inhibition on phytoplanktonic photosynthesis, we suggest operational quantum yield and electron transport rate as best parameters, once they were more sensitive to the DCMU toxicity.

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18

Sigfridsson, Kalle, Simon Young, and orjan Hansson. "Electron Transfer Between Spinach Plastocyanin Mutants and Photosystem 1." European Journal of Biochemistry 245, no. 3 (May 1997): 805–12. http://dx.doi.org/10.1111/j.1432-1033.1997.00805.x.

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19

McConnell, Michael D., John B. Cowgill, Patricia L. Baker, Fabrice Rappaport, and Kevin E. Redding. "Double Reduction of Plastoquinone to Plastoquinol in Photosystem 1." Biochemistry 50, no. 51 (December 27, 2011): 11034–46. http://dx.doi.org/10.1021/bi201131r.

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20

Shubin, V. V., N. V. Karapetyan, and A. A. Krasnovsky. "Molecular arrangement of pigment-protein complex of photosystem 1." Photosynthesis Research 9, no. 1-2 (1986): 3–12. http://dx.doi.org/10.1007/bf00029726.

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21

Allen, H., O. Hill, Nicholas J. Walton, and Davis Whitford. "The coupling of heterogeneous electron transfer to photosystem 1." Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 187, no. 1 (May 1985): 109–19. http://dx.doi.org/10.1016/0368-1874(85)85579-9.

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22

Eßmann, Vera, Fangyuan Zhao, Volker Hartmann, Marc M. Nowaczyk, Wolfgang Schuhmann, and Felipe Conzuelo. "In Operando Investigation of Electrical Coupling of Photosystem 1 and Photosystem 2 by Means of Bipolar Electrochemistry." Analytical Chemistry 89, no. 13 (June 22, 2017): 7160–65. http://dx.doi.org/10.1021/acs.analchem.7b01222.

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23

Berry, Matthew C., Peter J. Bratt, and Michael C. W. Evans. "Relaxation properties of the photosystem 1 electron transfer components: indications of the relative positions of the electron transfer cofactors in photosystem 1." Biochimica et Biophysica Acta (BBA) - Bioenergetics 1319, no. 2-3 (April 1997): 163–76. http://dx.doi.org/10.1016/s0005-2728(96)00157-0.

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24

Chow, W. S., J. M. Anderson, and A. Melis. "The Photosystem Stoichiometry in Thylakoids of Some Australian Shade-adapted Plant Species." Functional Plant Biology 17, no. 6 (1990): 665. http://dx.doi.org/10.1071/pp9900665.

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The concentrations of functional photosystem I1 (PSII) reaction centres in leaves and photosystem I reaction centres (P700) in thylakoids isolated from comparable leaves of Australian shade-adapted plant species of diverse taxa, life-forms and habitats were compared. The concentrations of PSII were determined directly in leaves by the oxygen yield per single-turnover flash in the presence of far-red background illumination. The concentrations of P700 were determined by the light-induced absorbance change of thylakoid membranes at 703 nm. On a chlorophyll basis, the amounts of both functional PSII and P700 were lower in shade species than in sun species. The PSII/PSI reaction centre stoichiometries of the shade species ranged from 1.2 to 1.9 indicating that (i) shade-adapted species do not have a fixed 1: 1 ratio; and (ii) their PSWPSI ratios are usually lower than those of sun species (1.7-1.8). We conclude that shade plants display variable photosystem stoichiometry. The results are discussed in terms of the interplay between the adjustment of photosystem stoichiometry and that of the light-harvesting chlorophyll antenna size of each photosystem in the thylakoid membrane of shade species.

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25

Andreeva, Atanaska S., Mira C. Busheva, Katerina V. Stoitchkova, and Iren K. Tzonova. "Photoinduced changes in photosystem II pigments." Journal of Physics: Conference Series 253 (November 1, 2010): 012065. http://dx.doi.org/10.1088/1742-6596/253/1/012065.

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26

Verma, Kavita, and Prasanna Mohanty. "Changes of the Photosynthetic Apparatus in Spirulina Cyanobacterium by Sodium Stress." Zeitschrift für Naturforschung C 55, no. 1-2 (February 1, 2000): 16–22. http://dx.doi.org/10.1515/znc-2000-1-205.

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Abstract Spirulina platensis trichomes grown in Zarrouks medium having total Na+ concentration as 0.14 ᴍ when transfered to fresh Zarrouks medium containing enhanced level of Na+ ions equal to 0.86 ᴍ showed 30% more accumulation of Na+ intracellularly as compared to the control. An inhibition of photosystem II activity to almost 66% was observed. Also due to this exposure to high Na+, the room temperature absorption characteristics of Spirulina trichomes and the thylakoid membrane preparations w ere altered indicating changes in the chromophore protein interactions and alterations in the phycocyanin/allophycocyanin ratio; there by affecting the energy harvest and energy transfer processes. An increase in the carotenoid absorption was two fold over the control in the treated sample. Similarly, room temperature and low temperature (77 K) fluorescence emission spectra collectively suggested alterations in the chlorophyll a emissions, F 726 of photosystem I reflecting changes in the lipid protein environment of the thylakoid. Our results indicate that in Spirulina the enhanced Na+ level alters the energy harvest and transfer processes. It also affected the emission characteristics of chlorophyll a of photosystem I.

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27

Boekema, Egbert J., Henny van Roon, and Jan P. Dekker. "Specific association of photosystem II and light-harvesting complex II in partially solubilized photosystem II membranes." FEBS Letters 424, no. 1-2 (March 6, 1998): 95–99. http://dx.doi.org/10.1016/s0014-5793(98)00147-1.

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28

Zhang, Meng-Meng, Da-Yong Fan, Keach Murakami, Murray R. Badger, Guang-Yu Sun, and Wah Soon Chow. "Partially Dissecting Electron Fluxes in Both Photosystems in Spinach Leaf Disks during Photosynthetic Induction." Plant and Cell Physiology 60, no. 10 (July 4, 2019): 2206–19. http://dx.doi.org/10.1093/pcp/pcz114.

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Abstract Photosynthetic induction, a gradual increase in photosynthetic rate on a transition from darkness or low light to high light, has ecological significance, impact on biomass accumulation in fluctuating light and relevance to photoprotection in strong light. However, the experimental quantification of the component electron fluxes in and around both photosystems during induction has been rare. Combining optimized chlorophyll fluorescence, the redox kinetics of P700 [primary electron donor in Photosystem I (PSI)] and membrane inlet mass spectrometry in the absence/presence of inhibitors/mediator, we partially estimated the components of electron fluxes in spinach leaf disks on transition from darkness to 1,000 ï¿½mol photonsï¿½m−2ï¿½s−1 for up to 10 min, obtaining the following findings: (i) the partitioning of energy between both photosystems did not change noticeably; (ii) in Photosystem II (PSII), the combined cyclic electron flow (CEF2) and charge recombination (CR2) to the ground state decreased gradually toward 0 in steady state; (iii) oxygen reduction by electrons from PSII, partly bypassing PSI, was small but measurable; (iv) cyclic electron flow around PSI (CEF1) peaked before becoming somewhat steady; (v) peak magnitudes of some of the electron fluxes, all probably photoprotective, were in the descending order: CEF1 > CEF2 + CR2 > chloroplast O2 uptake; and (vi) the chloroplast NADH dehydrogenase-like complex appeared to aid the antimycin A-sensitive CEF1. The results are important for fine-tuning in silico simulation of in vivo photosynthetic electron transport processes; such simulation is, in turn, necessary to probe partial processes in a complex network of interactions in response to environmental changes.

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29

Trebst, Achim. "The Topology of the Plastoquinone and Herbicide Binding Peptides of Photosystem II in the Thylakoid Membrane." Zeitschrift für Naturforschung C 41, no. 1-2 (February 1, 1986): 240–46. http://dx.doi.org/10.1515/znc-1986-1-235.

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Abstract The 32 kDa herbicide and QB binding peptide (D-1 protein) and its homologous 34 kDa peptide (D-2 protein) are integral membrane subunits of photosystem II. A model for their folding through the thylakoid membrane in five transmembrane a-helices is proposed from the comparison of amino acid sequence and hydropathy index plot homologies with subunits of the bacterial system. Following recent data on the X-ray structure of a bacterial photosystem the binding niche for QB is interpreted on the basis of the amino acid changes found in the 32 kDa peptide in herbicide tolerant higher plants and algae.

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30

Levitan, Orly, Muyuan Chen, Xuyuan Kuang, Kuan Yu Cheong, Jennifer Jiang, Melissa Banal, Nikhita Nambiar, et al. "Structural and functional analyses of photosystem II in the marine diatom Phaeodactylum tricornutum." Proceedings of the National Academy of Sciences 116, no. 35 (August 13, 2019): 17316–22. http://dx.doi.org/10.1073/pnas.1906726116.

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A descendant of the red algal lineage, diatoms are unicellular eukaryotic algae characterized by thylakoid membranes that lack the spatial differentiation of stroma and grana stacks found in green algae and higher plants. While the photophysiology of diatoms has been studied extensively, very little is known about the spatial organization of the multimeric photosynthetic protein complexes within their thylakoid membranes. Here, using cryo-electron tomography, proteomics, and biophysical analyses, we elucidate the macromolecular composition, architecture, and spatial distribution of photosystem II complexes in diatom thylakoid membranes. Structural analyses reveal 2 distinct photosystem II populations: loose clusters of complexes associated with antenna proteins and compact 2D crystalline arrays of dimeric cores. Biophysical measurements reveal only 1 photosystem II functional absorption cross section, suggesting that only the former population is photosynthetically active. The tomographic data indicate that the arrays of photosystem II cores are physically separated from those associated with antenna proteins. We hypothesize that the islands of photosystem cores are repair stations, where photodamaged proteins can be replaced. Our results strongly imply convergent evolution between the red and the green photosynthetic lineages toward spatial segregation of dynamic, functional microdomains of photosystem II supercomplexes.

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Kolli, Bala Krishna, Swati Tiwari, and Prasanna Mohanty. "Ultraviolet-B Induced Damage to Photosystem II in Intact Filaments of Spirulina platensis." Zeitschrift für Naturforschung C 53, no. 5-6 (June 1, 1998): 369–77. http://dx.doi.org/10.1515/znc-1998-5-611.

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Abstract When Spirulina platensis filaments were exposed to 0.75 mW.m-2.s-1 of ultraviolet-B radiation (the ultraviolet-B radiation under clear sky condition is ~1.0 mW.m-2.s-1), an inhibition in photosystem II activity was observed, the inhibition being 90% after 90 min exposure. Upon exposure to ultraviolet-B, the room temperature emission characteristics of Spirulina cells were altered when excited with light primarily absorbed by chlorophyll a or phycobilisomes. When the cells were exposed for 3 h the emission at 685 nm (F685), when excited at 440 nm (primarily chlorophyll a absorption), was enhanced compared to 715 nm (F 715) band of photosystem I suggesting a decrease in energy transfer from photosystem II to photosys tem I. Similarly, when the cells were excited at 580 nm (primarily the phycobilisomes), the ratio of emission intensity at 685 nm (F685) to that of 655 nm (F655) was decreased in the exposed cells. This change in emission characteristics seems to be linked with the uncoupling of the energy transfer from allophycocyanin to chlorophyll a of photosystem II. A small shift in emission peak positions was also indicated when excited either at 440 nm or 580 nm. Analysis of the fast induction of chlorophyll a transients in the presence and absence of 10 μm 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU) indicated that ultraviolet-B expo sure initially affects Qᴀ, the primary stable acceptor of photosystem II, and then the plastoquinone (PQ) pool. Our results on the loss in photosystem Il-catalyzed Hill activity with p-benzoquinone or dichlorobenzoquinone as electron acceptors also supports the contention that ultraviolet-B, even at low dose, initially alters the Qᴀ of photosystem II and subsequently PQ pool. The analysis of functional pool size of Spirulina suggests a substantial decrease in the functional pool size after 2 h UV-B exposure. These results indicate that in Spirulina low intensity of ultraviolet-B initially damages the reaction centre of photosystem II.

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32

Makewicz, A., A. Radunz, and G. H. Schmid. "Structural Modifications of the Photosynthetic Apparatus in the Region of Photosystem I in Nicotiana tabacum as a Consequence of an Increased CO2-Content of the Atmosphere." Zeitschrift für Naturforschung C 50, no. 7-8 (August 1, 1995): 511–20. http://dx.doi.org/10.1515/znc-1995-7-808.

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Nicotiana tabacum was grown with a CO2-content in the atmosphereof 350 ppm and 700 ppm. After three weeksof growth in the respective atmospherewe were able to show that chloroplasts from plants grown under 700 ppm CO2 exhibited an 18% higher photosystem I-mediatedelectron transport activity. Furthermore, we were able to show that in plants grown under the higher CO2-concentration the peptide composition of photosystem I had been quantitatively changed. It appeared that the CPI-peptides were increased, whereasthe LHCPI peptides were decreased. Corresponding to this change in the peptide composition the ratio chlorophyll/carotenoids/protein changes from 1:0.16:3.6 in the control plants to 1:0.23:5 in the “CO2-plants”. The chlorophyll a/b ratio changes from 1.9 in the control plants to 2.3 in the “CO2 plants”. Furthermore, the carotenoid composition appears to be changed, β-carotene increases by 60% as expected from the increased CPI-content. The xanthophylls lutein, violaxanthin, neoxanthin and zeaxanthin increase also but to a lesser extent. Using specific antisera to lipids, we were able to show that photosystem I contains only the membrane lipids monogalactosyldiglyceride and phosphatidylglycerol. Both lipids are specifically bound in a restricted number onto peptides of the photosystem I complex. Both lipids differ with respect to their binding strength on the peptides of photosystem I. The changes in the peptide and lipid composition were established by chemical analyses and by immunological techniques (Western blot) using monospecific antisera to the photosystem I peptides, to the chloroplast lipids as well as to the chloroplast carotenoids. From the quantitative and qualitative analyses of the peptides, carotenoids and lipids, the molecular distribution of the carotenoids and lipids in the CPI and LHCPI complex of photosystem I was established.

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Albertsson, Per-Åke, and Shi-Gui Yu. "Heterogeneity among photosystem IIα. Isolation of thylakoid membrane vesicles with different functional antennae size of photosystem IIα." Biochimica et Biophysica Acta (BBA) - Bioenergetics 936, no. 2 (November 1988): 215–21. http://dx.doi.org/10.1016/0005-2728(88)90238-1.

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34

Takeuchi, TS, and JP Thornber. "Heat-Induced Alterations in Thylakoid Membrane Protein Composition in Barley." Functional Plant Biology 21, no. 6 (1994): 759. http://dx.doi.org/10.1071/pp9940759.

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Biochemical and spectroscopic studies on the effects of high temperatures (45-47� C) over a 1 h period on the protein composition, fluorescence and photochemical activities of the barley thylakoid membrane were made. Photosystem II (PS II) activity decreased as expected, and photosystem I (PS I) activity also unexpectedly decreased. Our data support previous conclusions that the decrease in PS I activity is largely due to inactivation (or loss) of a component between the two photosystems. A two-dimensional electrophoretic system permitted first the separation of the thylakoid pigment-protein complexes of unstressed and stressed plants, followed by a determination of their subunit composition. The changes in the protein composition of each pigment-protein complex in response to elevated temperatures were monitored. Heat changed the quaternary structure of PS II and resulted in removal of the oxygen-evolving enhancer proteins from the thylakoid, but did essentially no damage to the PS I complex. The PS II core complex dissociated from a dimeric form to a monomeric one, and the major LHC II component (LHC IIb) changed from a trimeric to a monomeric form. The pigments that are lost from thylakoids during heat stress are mainly removed from the PS II pigment-proteins.

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35

Badura, Adrian, Dmitrii Guschin, Tim Kothe, Marta J. Kopczak, Wolfgang Schuhmann, and Matthias Rögner. "Photocurrent generation by photosystem 1 integrated in crosslinked redox hydrogels." Energy & Environmental Science 4, no. 7 (2011): 2435. http://dx.doi.org/10.1039/c1ee01126j.

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36

Kruip, Jochen, Parag R. Chitnis, Bernard Lagoutte, Matthias Rögner, and Egbert J. Boekema. "Structural Organization of the Major Subunits in Cyanobacterial Photosystem 1." Journal of Biological Chemistry 272, no. 27 (July 4, 1997): 17061–69. http://dx.doi.org/10.1074/jbc.272.27.17061.

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37

Gobets, Bas, and Rienk van Grondelle. "Energy transfer and trapping in photosystem I." Biochimica et Biophysica Acta (BBA) - Bioenergetics 1507, no. 1-3 (October 2001): 80–99. http://dx.doi.org/10.1016/s0005-2728(01)00203-1.

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38

Kufryk, Galyna I., and Wim F. J. Vermaas. "Slr2013 Is a Novel Protein Regulating Functional Assembly of Photosystem II in Synechocystis sp. Strain PCC 6803." Journal of Bacteriology 185, no. 22 (November 15, 2003): 6615–23. http://dx.doi.org/10.1128/jb.185.22.6615-6623.2003.

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ABSTRACT The Synechocystis sp. strain PCC 6803, which has a T192H mutation in the D2 protein of photosystem II, is an obligate photoheterotroph due to the lack of assembled photosystem II complexes. A secondary mutant, Rg2, has been selected that retains the T192H mutation but is able to grow photoautotrophically. Restoration of photoautotrophic growth in this mutant was caused by early termination at position 294 in the Slr2013 protein. The T192H mutant with truncated Slr2013 forms fully functional photosystem II reaction centers that differ from wild-type reaction centers only by a 30% higher rate of charge recombination between the primary electron acceptor, QA −, and the donor side and by a reduced stability of the oxidized form of the redox-active Tyr residue, YD, in the D2 protein. This suggests that the T192H mutation itself did not directly affect electron transfer components, but rather affected protein folding and/or stable assembly of photosystem II, and that Slr2013 is involved in the folding of the D2 protein and the assembly of photosystem II. Besides participation in photosystem II assembly, Slr2013 plays a critical role in the cell, because the corresponding gene cannot be deleted completely under conditions in which photosystem II is dispensable. Truncation of Slr2013 by itself does not affect photosynthetic activity of Synechocystis sp. strain PCC 6803. Slr2013 is annotated in CyanoBase as a hypothetical protein and shares a DUF58 family signature with other hypothetical proteins of unknown function. Genes for close homologues of Slr2013 are found in other cyanobacteria (Nostoc punctiforme, Anabaena sp. strain PCC 7120, and Thermosynechococcus elongatus BP-1), and apparent orthologs of this protein are found in Eubacteria and Archaea, but not in eukaryotes. We suggest that Slr2013 regulates functional assembly of photosystem II and has at least one other important function in the cell.

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39

Nitschke, Wolfgang, Ute Feiler, Wolfgang Lockau, and Günter Hauska. "The photosystem of the green sulfur bacterium Chlorobium limicola contains two early electron acceptors similar to photosystem I." FEBS Letters 218, no. 2 (June 29, 1987): 283–86. http://dx.doi.org/10.1016/0014-5793(87)81062-1.

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40

Kusuma, D. Y., Q. Hidayah, A. N. Izziyah, and B. Purnama. "Integration of photosystem I and photosystem II from tylakoid membrane of spirulina sp. for DSSC natural dye pigments." Journal of Physics: Conference Series 1563 (June 2020): 012008. http://dx.doi.org/10.1088/1742-6596/1563/1/012008.

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41

Lumian, Jessica E., Anne D. Jungblut, Megan L. Dillion, Ian Hawes, Peter T. Doran, Tyler J. Mackey, Gregory J. Dick, Christen L. Grettenberger, and Dawn Y. Sumner. "Metabolic Capacity of the Antarctic Cyanobacterium Phormidium pseudopriestleyi That Sustains Oxygenic Photosynthesis in the Presence of Hydrogen Sulfide." Genes 12, no. 3 (March 16, 2021): 426. http://dx.doi.org/10.3390/genes12030426.

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Sulfide inhibits oxygenic photosynthesis by blocking electron transfer between H2O and the oxygen-evolving complex in the D1 protein of Photosystem II. The ability of cyanobacteria to counter this effect has implications for understanding the productivity of benthic microbial mats in sulfidic environments throughout Earth history. In Lake Fryxell, Antarctica, the benthic, filamentous cyanobacterium Phormidium pseudopriestleyi creates a 1–2 mm thick layer of 50 µmol L−1 O2 in otherwise sulfidic water, demonstrating that it sustains oxygenic photosynthesis in the presence of sulfide. A metagenome-assembled genome of P. pseudopriestleyi indicates a genetic capacity for oxygenic photosynthesis, including multiple copies of psbA (encoding the D1 protein of Photosystem II), and anoxygenic photosynthesis with a copy of sqr (encoding the sulfide quinone reductase protein that oxidizes sulfide). The genomic content of P. pseudopriestleyi is consistent with sulfide tolerance mechanisms including increasing psbA expression or directly oxidizing sulfide with sulfide quinone reductase. However, the ability of the organism to reduce Photosystem I via sulfide quinone reductase while Photosystem II is sulfide-inhibited, thereby performing anoxygenic photosynthesis in the presence of sulfide, has yet to be demonstrated.

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42

Melis, Anastasios, Conrad W. Mullineaux, and John F. Allen. "Acclimation of the Photosynthetic Apparatus to Photosystem I or Photosystem II Light: Evidence from Quantum Yield Measurements and Fluorescence Spectroscopy of Cyanobacterial Cells." Zeitschrift für Naturforschung C 44, no. 1-2 (February 1, 1989): 109–18. http://dx.doi.org/10.1515/znc-1989-1-219.

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Abstract Cells of the cyanobacterium Synechococcus 6301 were grown under illumination whose spectral composition favoured absorption either by the phycobilisome (PBS) light-harvesting antenna of photosystem II (PS II) or by the chlorophyll (Chi) a light-harvesting antenna of photosystem I (PS I). Cells grown under PS I-light developed relatively high PS II/PS I and PBS/Chl ratios. Cells grown under PS II-light developed relatively low PS II/PS I and PBS/Chl ratios. Thus, the primary difference between cells in the two acclimation states appeared to be the relative concentration of PBS-PS II and PS I complexes in the thylakoid membrane. Measurements of the quantum yield of oxygen evolution suggested a higher efficiency of cellular photosynthesis upon the adjustment of photosystem stoichiometry to a specific light condition. The quantum yield of oxygen evolution was nevertheless lower under PBS than Chi excitation, suggesting quenching of excitation energy in the photochemical apparatus of PS II in Synechococcus 6301. This phenomenon was more pronounced in the PS II-light than in the PS I-light grown cells. Room temperature and 77 K fluorescence emission spectroscopy indicated that excess excitation energy in the PBS was not transferred to PS I, suggesting the operation of a non-radiative and non-photochemical decay of excitation energy at the PBS-PS II complex. This non-photochemical quenching was specific to conditions where excitation of PS II occurred in excess of its capacity for useful photochemistry.

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43

Tevini, M., and K. Pfister. "Inhibition of Photosystem II by UV-B-Radiation." Zeitschrift für Naturforschung C 40, no. 1-2 (February 1, 1985): 129–33. http://dx.doi.org/10.1515/znc-1985-1-225.

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Abstract The effect of UV-B-radiation on PSII activity of spinach chloroplasts was analyzed by measuring the integrity of the herbicide-binding protein (HBP 32), by measurement of fluorescence induction in the presence of Diuron (DCMU), and by mathematical analysis of the fluorescence induction curves. It was shown that UV-B inactivates the PSII α-centers but not PSII β-centers. However, the possibility cannot be excluded that in addition the donor site of PSII near the reaction center is attacked by UV-B-radiation.

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44

Wu, Jianghao, Liwei Rong, Weijun Lin, Lingxi Kong, Dengjie Wei, Lixin Zhang, Jean-David Rochaix, and Xiumei Xu. "Functional redox links between lumen thiol oxidoreductase1 and serine/threonine-protein kinase STN7." Plant Physiology 186, no. 2 (February 23, 2021): 964–76. http://dx.doi.org/10.1093/plphys/kiab091.

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Abstract In response to changing light quantity and quality, photosynthetic organisms perform state transitions, a process which optimizes photosynthetic yield and mitigates photo-damage. The serine/threonine-protein kinase STN7 phosphorylates the light-harvesting complex of photosystem II (PSII; light-harvesting complex II), which then migrates from PSII to photosystem I (PSI), thereby rebalancing the light excitation energy between the photosystems and restoring the redox poise of the photosynthetic electron transport chain. Two conserved cysteines forming intra- or intermolecular disulfide bonds in the lumenal domain (LD) of STN7 are essential for the kinase activity although it is still unknown how activation of the kinase is regulated. In this study, we show lumen thiol oxidoreductase 1 (LTO1) is co-expressed with STN7 in Arabidopsis (Arabidopsis thaliana) and interacts with the LD of STN7 in vitro and in vivo. LTO1 contains thioredoxin (TRX)-like and vitamin K epoxide reductase domains which are related to the disulfide-bond formation system in bacteria. We further show that the TRX-like domain of LTO1 is able to oxidize the conserved lumenal cysteines of STN7 in vitro. In addition, loss of LTO1 affects the kinase activity of STN7 in Arabidopsis. Based on these results, we propose that LTO1 helps to maintain STN7 in an oxidized active state in state 2 through redox interactions between the lumenal cysteines of STN7 and LTO1.

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45

Jimenez, A., R. Mata, B. Lotina-Hennsen, and A. L. Anaya. "Interference of l,2,3,4-Tetramethoxy-5-(2-propenyl)benzene with Photosynthetic Electron Transport." Zeitschrift für Naturforschung C 53, no. 1-2 (February 1, 1998): 55–59. http://dx.doi.org/10.1515/znc-1998-1-211.

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AbstractThe effect of 1,2,3,4-tetramethoxy-5-(2-propenyl)benzene, the major phytogrowth-inhibitory agent isolated from the leaves, stem bark and wood of Malmea depressa (Annonaceae), on several photosynthetic activities has been investigated using freshly lysed spinach chloroplasts. The results indicate that this compound inhibits proton-uptake, ATP synthesis and electron flow (basal, phosphorylating and uncoupled) in a concentration dependent manner, therefore acting as a Hill reaction inhibitor. Uncoupled electron transport through photosystem I from reduced dichlorophenol-indophenol to methylviologen is unaffected by this compound. On the other hand, uncoupled electron transport through photosystem II from water to dichlorophenol-indophenol, from water to silicomolibdate and from diphenylcarbazide to dichlorophenol-indophenol is inhibited by this phenylpropanoid, suggesting that the site of inhibition is located in the span from P680 to QA.

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46

Gau, Achim E., Gudrun Wälzlein, Susanne Gärtner, Matthias Kuhlmann, Susanne Specht, and Elfriede K. Pistorius. "Immunological Identification of Polypeptides in Photosystem II Complexes from the Cyanobacterium Anacystis nidulans." Zeitschrift für Naturforschung C 44, no. 11-12 (December 1, 1989): 971–75. http://dx.doi.org/10.1515/znc-1989-11-1216.

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Abstract Photosystem II complexes from the cyanobacterium Anacystis nidulans have been investigated by Western blots with antisera raised against four photosystem II peptides from plants and with an antiserum raised against the soluble L-amino acid oxidase protein from/1. nidulans to achieve an identification of the polypeptides - especially of the L-amino acid oxidase related protein - in isolated photosystem II complexes. Anacystis photosystem II complexes which were solubilized with lauryldimethylamine N-oxide and purified by sucrose cushion and sucrose gradient centrifugation, contained as major Coomassie brilliant blue stained polypeptides a 71 kDa band of unknown identity, a 62 kDa band, which partly contained D-l, a 55 and 49 kDa band which were immuno-reactive with an antiserum to the 47 kDa peptide of tobacco PS II complexes, and three distinct bands in the 30 kDa region. These latter bands could be identified as the extrinsic Mn stabilizing peptide (27-30 kDa), D-l (30-33 kDa) and a 36 kDa peptide (35 - 38 kDa) which crossreacted with the antiserum raised against the soluble L-amino acid oxidase protein of 50 kDa. These results suggest that the 36 kDa peptide present in purified photosystem II complexes from A. nidulans might be a processed form of the soluble 50 kDa L-amino acid oxidase protein.

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47

Colón-López, Milagros S., and Louis A. Sherman. "Transcriptional and Translational Regulation of Photosystem I and II Genes in Light-Dark- and Continuous-Light-Grown Cultures of the Unicellular Cyanobacterium Cyanothece sp. Strain ATCC 51142." Journal of Bacteriology 180, no. 3 (February 1, 1998): 519–26. http://dx.doi.org/10.1128/jb.180.3.519-526.1998.

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ABSTRACT Cyanothece sp. strain ATCC 51142, a unicellular, diazotrophic cyanobacterium, demonstrated extensive metabolic periodicities of photosynthesis, respiration, and nitrogen fixation when grown under N2-fixing conditions. This report describes the relationship of the biosynthesis of photosynthesis genes to changes in the oligomerization state of the photosystems. Transcripts of the psbA gene family, encoding the photosystem II (PSII) reaction center protein D1, accumulated primarily during the light period, and net transcription reached a peak between 2 to 6 h in the light in light-dark (LD) growth and between 4 to 10 h in the subjective light when grown under continuous light (LL). The relative amount of the D1 protein (form 1 versus form 2) appeared to change during this diurnal cycle, along with changes in the PSII monomer/dimer ratio. D1 form 1 accumulated at approximately equal levels throughout the 24-h cycle, whereas D1 form 2 accumulated at significantly higher levels at approximately 8 to 10 h in the light or subjective light. The psbD gene, encoding the reaction center protein D2, also demonstrated differences between the two copies of this gene, with one copy transcribed more heavily around 6 to 8 h in the light. Accumulation of the PSI reaction center proteins PsaA and PsaB was maximal in the dark or subjective-dark periods, a period during which PSI was primarily in the trimeric form. We conclude that photosystem organization changes during the diurnal cycle to favor either noncyclic electron flow, which leads to O2 evolution and CO2 fixation, or cyclic electron flow, which favors ATP synthesis.

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48

Nikandrov, V. V., Ya V. Borisova, E. A. Bocharov, M. A. Usachev, G. V. Nizova, V. A. Nadtochenko, E. P. Lukashev, et al. "Photochemical properties of photosystem 1 immobilized in a mesoporous semiconductor matrix." High Energy Chemistry 46, no. 3 (May 2012): 200–205. http://dx.doi.org/10.1134/s0018143912030095.

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49

Rigby, Stephen E. J., Michael C. W. Evans, and Peter Heathcote. "ENDOR and Special Triple Resonance Spectroscopy of A1•-of Photosystem 1†." Biochemistry 35, no. 21 (January 1996): 6651–56. http://dx.doi.org/10.1021/bi952619x.

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50

Kovalenko, Ilya B., Anna M. Abaturova, Galina Yu Riznichenko, and Andrei B. Rubin. "Computer simulation of interaction of photosystem 1 with plastocyanin and ferredoxin." Biosystems 103, no. 2 (February 2011): 180–87. http://dx.doi.org/10.1016/j.biosystems.2010.09.013.

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