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  • 11
    ISSN: 1573-5079
    Keywords: photosynthesis ; thermal emission ; P700 ; quantum yield ; energy conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thermal emission and photochemical energy storage were examined in photosystem I reaction center/core antenna complexes (about 40 Chl a/P700) using photoacoustic spectroscopy. Satisfactory signals could only be obtained from samples bound to hydroxyapatite and all samples had a low signal-to-noise ratio compared to either PS I or PS II in thylakoid membranes. The energy storage signal was saturated at low intensity (half saturation at 1.5 W m-2) and predicted a photochemical quantum yield of 〉90%. Exogenous donors and acceptors had no effect on the signal amplitudes indicating that energy storage is the result of charge separation between endogenous components. Fe(CN)6 -3 oxidation of P700 and dithionite-induced reduction of acceptors FA-FB inhibited energy storage. These data are compatible with the hypothesis that energy storage in PS I arises from charge separation between P700 and Fe-S centers FA-FB that is stable on the time scale of the photoacoustic modulation. High intensity background light (160 W m-2) caused an irreversible loss of energy storage and correlated with a decrease in oxidizable P700; both are probably the result of high light-induced photoinhibition. By analogy to the low fluorescence yield of PS I, the low signal-to-noise ratio in these preparations is attributed to the short lifetime of Chl singlet excited states in PS I-40 and its indirect effect on the yield of thermal emission.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1573-5079
    Keywords: electron transport ; oxygen uptake ; Photosystem I ; superoxide radicals ; superoxide dismutase ; heat stress ; electron donors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A Photosystem I submembrane fraction isolated from spinach was used to study the mechanism of heat-stress stimulation of oxygen uptake by the photosystem. Various artificial electron donors were shown to generate electron transport reactions with various degrees of thermally induced stimulation. A strong stimulation was observed with durohydroquinone as electron donor with a maximal effect at 50 °C. The degree of stimulation obtained was independent from the redox potential of the electron donors and from their oxidation site because the enzyme superoxide dismutase fully inhibited the stimulation. Instead, it is proposed that thermal stress causes the release of membrane bound superoxide dismutase from the thylakoids thus allowing the reduced form of electron donors with specific properties to reduce O2 − radicals to H2O2 besides the usual disproportionation of O2 − into O2 and H2O2.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Photosynthesis research 23 (1990), S. 313-318 
    ISSN: 1573-5079
    Keywords: thylakoid membranes ; electron transfer ; photoacoustic spectroscopy ; energy storage ; photosynthesis ; plastoquinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The photosynthetic energy storage yield of uncoupled thylakoid membranes was monitored by photoacoustic spectroscopy at various measuring beam intensities. The energy storage rate as evaluated by the half-saturation measuring beam intensity (i50) was inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea, by heat inactivation or by artificial electron acceptors specific for photosystem I or photosystem II; and was activated by electron donors to photosystem I. The reactions involving both photosystems were all characterized by a similar maximal energy storage yield of 16±2 percent. The data could be interpreted if we assumed that the energy storage elicited by the photosystems at 35 Hz is detected at the level of the plastoquinone pool.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Photosynthesis research 30 (1991), S. 123-130 
    ISSN: 1573-5079
    Keywords: oxygen evolution ; calcium ; chloride ; electron transport ; photosynthetic inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The inhibitory effect of Zn2+ on photosynthetic electron transport was investigated in native and CaCl2-treated (depleted in extrinsic polypeptides) Photosystem II (PS II) submembrane preparations. Inhibition of 2,6-dichlorophenolindophenol photoreduction by Zn2+ was much stronger in protein-depleted preparations in comparison to the native form. It was found that Ca2+ significantly reduced the inhibition in the native PS II preparations, as did Mn2+ in a combination with H2O2 in the protein-depleted counterparts. No other tested monovalent or divalent cations could replace Ca2+ or Mn2+ in the respective experiments. Diphenylcarbazide could partially relieve (40–45%) the inhibition in both types of preparations. The above indicates the presence of an active Zn2+ inhibitory site on the donor side of PS II. However, neither Ca2+ nor Mn2+ could completely prevent inhibition by high concentrations of Zn2+ (〉1 mM). We propose that elevated levels of Zn2+ strongly perturb the conformation of the PS II core complex and might also affect the acceptor side of the photosystem.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 32 (1988), S. 64-67 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Photoacoustic spectroscopy was used to monitor photo synthetic electron transfer in native and immobilized thylakoid membranes. The photoacoustic parameter φr′ (the percentage of absorbed energy that is stored in photo chemical intermediates) and i50 (the half-saturation modulated light intensity) were directly correlated to electron transfer rates. As previously shown, thylakoids immobilized in an albumin-glutaraldehyde matrix were more resistant to aging. The inhibitory effects of the immobilization procedure and of aging at 4°C were detected as a decrease in i50 values. In analogy with enzyme kinetic analysis, the effect could be characterized as a competitive type of inhibition. Photoacoustic measurements are performed in conditions similar to a working bioreactor cell with regards to the sample preparation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 178-183 
    ISSN: 0006-3592
    Keywords: bioassay ; phytotoxicity ; photosynthesis ; immobilized membranes ; oxygen evolution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The potential of thylakoid membranes immobilized in an albumin-glutaraldehyde crosslinked matrix in a fast bioassay for phytotoxicity measurements in aqueous samples is studied. Free and immobilized preparations are compared for their electron transport activity measured as the initial rate of oxygen evolution with 2,5-cichlorobenzoquinone as the artificial electron acceptor. Immobilized thylakoids were much stable under storage conditions; in the dark, at 4°C, they were fully stable in terms of photosynthetic activity for a period of 200 h. The immobilized membranes were as sensitive as the free thylakoids for the detection of most of the compounds tested (metal cations, sulfite, nitrite, and herbicides), all known as inhibitors of photosynthetic electron transport. In some instances, the immobilized preparations were even more sensitive than the free counterparts. The sensitivity could be further increased by lowering chlorophyll concentration in the assay. The short incubation period required (∼10 to 15 min) and the small volume of the assay (3 mL) suggest that this type of material should be useful in the detection of locations or effluents with phytotoxic character. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A thylakoids containing photoelectrochemical cell was used to monitor the photocurrent under photentiostatic mode using specific electron donnors and acceptors, and inhibitors of electron transfer. It is shown that both photosystem I and II can generate a photocurrent under the appropriate conditions. The photocurrent was also monitored in the absence of oxygen evolution thus suggesting a possible application for hydrogenase catalysed hydrogen production.
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 1573-6784
    Keywords: cyanobacterium ; immobilization ; photoelectrochemical cell ; poly(vinylalcohol) ; pollutant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A cyanobacterium, Synechocystis sp. PCC 6803, was immobilized by entrapment in poly(vinylalcohol) bearing styrylpyridinium groups. Its properties in a single-compartment micro-photoelectrochemical cell using platinum electrodes in potentiosatic mode were compared with the native material. The operational activity was measured in the presence of an electrolytic solution containing 20 mM sodium phosphate, 0.15 mM NaCl and 1 mM MgCl2. The best conditions of use are pH 7.0, 38 °C and a 2,5-dichlorobenzoquinone concentration equal to 350 μM with native cyanobacteria or pH 6.5, 25 °C and 500 μM 2,5-dichlorobenzoquinone after entrapment. Using this procedure, the photocurrent could be inhibited by pollutants such as Diuron or HgCl2. After entrapment, the detection limits (corresponding to a 10% inhibition) were respectively 0.5 μM and 50 μM for Diuron and HgCl2 after five minutes of incubation. A permeabilization technique was used to increase sensitivity of the procedure to the detection of HgCl2 (25% inhibition with 50 μM after five minutes of incubation).
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Biotechnology techniques 4 (1990), S. 363-368 
    ISSN: 1573-6784
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Thylakoid membranes isolated from spinach leaves were used as the biological sensing material to elaborate a biosensor for the detection of small amount of the herbicides atrazine and diuron. Free and immobilized thylakoid membranes were compared for their responses to inhibition by herbicides by following the variation of the photocurrent. Immobilized thylakoid membranes were twice as sensitive to inhibition by herbicides than the native thylakoids.
    Type of Medium: Electronic Resource
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  • 20
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Thylakoid membranes immobilized in an albumin-glutaraldehyde cross-linked matrix were used for photocurrent generation by a photoelectrochemical cell in potentiostatic mode. This type of preparation was quite suited for such application because it retains a substantial volume of electrolyte within the porous network formed. This property allowed for introducing electron transfer inhibitors and artificial electron acceptors and further it permitted proper migration of electroactive species from the thylakoid membranes to the working electrode as required for efficient photocurrent generation.
    Type of Medium: Electronic Resource
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