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  • 1
    Electronic Resource
    Electronic Resource
    Electron uptake and delivery sites on plastocyanin in its reactions with the photosynthetic electron transport system (1982)
    s.l. : American Chemical Society
    Biochemistry 21 (1982), S. 1885-1890 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00537a028
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  • 2
    Electronic Resource
    Electronic Resource
    Chilling-induced leaf abscission of Ixora coccinea plants. III. Enhancement by high light via increased oxidative processes (2001)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 113 (2001), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The role of increased oxidation induced by successive stresses of chilling and high light in the induction of leaf abscission was studied in Ixora coccinea plants in relation to auxin metabolism and oxidative processes. Exposure of plants following dark chilling (7°C for 3 days) to high light (500–700 μmol m−2 s−1 photosynthetically active radiation) for 5 h at 20–25°C enhanced chilling-induced leaf abscission. This abscission was inhibited by pretreatment with the antioxidant butylated hydroxyanisole, α-naphthaleneacetic acid or the ethylene action inhibitor, 1-methylcyclopropene. The oxidative processes initiated during the low light period following the dark chilling period, such as indoleacetic acid (IAA) decarboxylation and lipid peroxidation, were further enhanced by subsequent exposure to high light. Photoinhibition, expressed by the reduction of the chlorophyll fluorescence parameter Fv/Fm, was evident following exposure to high light, irrespective of the temperature of the pretreatment, but this reduction persisted only in chilled plants. This suggests that oxidative processes generated during and after the chilling period might have inhibited the recovery from photoinhibition. The chilling stress under darkness induced a 60% reduction in superoxide dismutase (SOD) activity and significant increases (130–600%) in the activities of several other antioxidative enzymes. These data suggest that the chilling-induced reduction in SOD activity may well be responsible for the increase in the oxidative stress induced by the subsequent light treatment, as expressed by the increased enzymatic activities. Taken together, this study provides further support for the involvement of oxidative processes in the events occurring in tissues exposed to sequential chilling and light stresses, leading to reduction in free IAA content in the abscission zone and to leaf abscission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2001.1130306.x
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  • 3
    Electronic Resource
    Electronic Resource
    Electrogenic and electroneutral transport modes of renal Na/K ATPase reconstituted into proteoliposomes (1990)
    Springer
    The journal of membrane biology 113 (1990), S. 139-154 
    Details
    ISSN: 1432-1424
    Keywords: Na/K-pump ; electrogenicity ; reconstituted vesicles ; variable coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary This paper describes measurements of electrical potentials generated by renal Na/K-ATPase reconstituted into proteoliposomes, utilizing the anionic dye, oxonol VI. Calibration of absorption changes with imposed diffusion potentials allows estimation of absolute values of electrogenic potentials. ATP-dependent Nacyt/Kexc exchange in K-loaded vesicles generates large potentials, up to 250 mV. By comparing initial rates or steady-state potentials with ATP-dependent22Na fluxes in different conditions, it is possible to infer whether coupling ratios are constant or variable. For concentrations of Nacyt (2–50mm) and ATP (1–1000 μm) and pH's (6.5–8.5), the classical 3Nacyt/2Kexc coupling ratio is maintained. However, at low Nacyt concentrations (〈0.8mm), the coupling ratio is apparently less than 3Nacyt/2Kexc. ATP-dependent Nacyt/congenerexc exchange in vesicles loaded with Rb, Cs, Li and Na is electrogenic. In this mode congeners, including Naexc, act as Kexc surrogates in an electrogenic 3Nacyt/2congenerexc exchange. (ATP+Pi)-dependent Kcyt/Kexc exchange in K-loaded vesicles is electroneutral. ATP-dependent “uncoupled” Na flux into Na- and K-free vesicles is electroneutral at pH 6.5–7.0 but becomes progressively electrogenic as the pH is raised to 8.5. The22Na flux shows no anion specificity. We propose that “uncoupled” Na flux is an electroneutral 3Nacyt/3Hexc exchange at pH 6.5–7.0 but at higher pH's the coupling ratio changes progressively, reaching 3Na/no ions at pH 8.5. Slow passive pump-mediated net K uptake into Na- and K-free vesicles is electroneutral, and may also involve Kcyt/Hexc exchange. We propose the general hypothesis that coupling ratios are fixed when cation transport sites are saturated, but at low concentrations of transported cations, e.g., Nacyt in Na/K exchange and Hexc in “uncoupled” Na flux, coupling ratios may change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872888
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  • 4
    Electronic Resource
    Electronic Resource
    Reverse electron flow in chloroplasts (1986)
    Springer
    Photosynthesis research 10 (1986), S. 405-413 
    Details
    ISSN: 1573-5079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Energy dependent reverse electron flow reactions in isolated thylakoids provide a unique tool to study, in the dark, the coupling between the ATP synthase, proton transport and the electron transfer system. Appropriate experimental conditions have been established to follow experimentally the following reactions: 1. ATP driven proton uptake into the inner-thylakoid space, which requires preactivation of the ATP synthase. 2. ATP driven reverse electron transport, which involves proton transport as an intermediate, and results in the reduction of QA by an externally added electron donor. 3. ATP driven luminescence, which requires the presence of an oxidized partner on the water side of photosystem II, and involves electron transport from QB to QA. 4. ΔpH driven reverse electron flow, which does not require the participation of the ATP synthase, and uses reduced intermediates between the two photosystems as electron donors for the reduction of QA. 5. ΔpH driven luminescence which again uses reduced intermdiates between the two photosystems as electron donors for QA reduction, and requires the presence of an oxidized partner on the water side of photosystem II. Several of these reactions have been shown to occur in intact chloroplasts and may provide an important regulatory mechanism in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00118306
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  • 5
    Electronic Resource
    Electronic Resource
    Circularly polarized chlorophyll luminescence reflects the macro-organization of grana in pea chloroplasts (2000)
    Springer
    Photosynthesis research 65 (2000), S. 83-92 
    Details
    ISSN: 1573-5079
    Keywords: circular dichroism ; emission anisotropy factor ; ionic strength ; osmotic pressure ; photoinhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Circular polarization of luminescence (CPL; Steinberg IZ (1978) Annu Rev Biophys Bioeng 7: 113–137) was applied to study pea chloroplasts in different structural states. The structural changes of chloroplasts were induced by variation of osmotic pressure, concentration of magnesium-ions or photoinhibition. Both large CPL and psi-type circular dichroism (psi, polymerization and salt induced) signals appeared in the presence of granal macrostructure and were sensitive to structural changes of the grana. The relation was studied between the amount of CPL expressed as an emission anisotropy factor g em and amplitudes of the red psi-type CD bands. The positive psi-type CD band was not directly correlated with g em possibly due to a large contribution of circular intensity differential scattering to the measured CD spectra. However, a linear correlation between the amplitude of the negative psi-type CD band and g em was found. The CPL signal of pea chloroplasts was attributed to a psi-type origin, which is observed in macroaggregates with densely packed chromophores with a long-range chiral order, and directly depends on the level of macroorganization. With the use of CPL-based microscopy, the long-range packing of LHC II particles can be studied in individual chloroplasts in future. In addition, the CPL method in general allows the study of the macro-organization of grana in green leaves, where conventional light-transmission methods fail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006441719869
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  • 6
    Electronic Resource
    Electronic Resource
    Irreversible disassembly of chiral macrodomains in thylakoids due to photoinhibition (1997)
    Springer
    Photosynthesis research 51 (1997), S. 119-126 
    Details
    ISSN: 1573-5079
    Keywords: chiral macroorganization ofchromophores ; circular dichroism ; chlorophyllfluorescence induction ; photoinhibition ofphotosynthesis ; spinach thylakoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We investigated the effect of photoinhibitory illumination on the chiral macroorganization of the chromophores in spinach thylakoid membranes. By measuring circular dichroism (CD), we found that prolonged (15 min) illumination of membranes with intense white light led to irreversible diminishment of the main CD bands originating from the chiral macroorganization of the chromophores. The irreversible decrease of the main CD bands showed a nearly linear correlation with the extent of photoinhibition which was determined by chlorophyll fluorescence induction. CD measurements also revealed that the excitonic CD bands, which are given rise by short-range interactions between the chromophores inside the complexes or particles, were largely insensitive to the photoinhibitory illumination of the membranes. These data show that, whereas photoinhibitory treatment has no perceptible effect on the molecular architecture of the bulk of the pigment–protein complexes, it leads to a disorganization of their macroarray, and an irreversible disassembly of the chirally organized macrodomains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005775720376
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  • 7
    Electronic Resource
    Electronic Resource
    Sulfide-quinone and sulfide-cytochrome reduction in Rhodobacter capsulatus (1994)
    Springer
    Photosynthesis research 39 (1994), S. 175-181 
    Details
    ISSN: 1573-5079
    Keywords: sulfide-quinone reductase (SQR) ; Oselllatoria limnetiea ; Chlorobium limicola ; electron transport ; LED array spectrophotometer ; anoxygenic photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reduction by sulfide of exogenous ubiquinone is compared to the reduction of cytochromes in chromatophores of Rhodobacter capsulatus. From titrations with sulfide values for Vmax of 300 and 10 μmoles reduced/mg bacteriochlorophyll a·h, and for Km of 5 and 3 μM were estimated, for decyl-ubiquinone-and cytochrome c-reduction, respectively. Both reactions are sensitive to KCN, as has been found for sulfide-quinone reductase (SQR) in Oscillatoria limnetica, which is a flavoprotein. Effects of inhibitors interfering with quinone binding sites suggest that at least part of the electron transport from sulfide in R. capsulatus employs the cytochrome bc 1-complex via the ubiquinone pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029384
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  • 8
    Electronic Resource
    Electronic Resource
    Reduction of cytochromes with menaquinol and sulfide in membranes from green sulfur bacteria (1995)
    Springer
    Photosynthesis research 43 (1995), S. 27-34 
    Details
    ISSN: 1573-5079
    Keywords: sulfide-quinone reductase (SQR) ; electron transport ; Chlorobium ; oxidant-induced reduction of cytochrome b ; cytochrome bc-complex ; menaquinone ; antimycin ; stigmatellin ; NQNO ; anoxygenic photosynthesis ; LED array spectrophotometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Reduction of cytochromes in chlorosome-free membranes of Chlorobia was studied anaerobically, with an LED array spectrophotometer. For Chlorobium tepidum these membranes contained 0.2 moles cytochrome per mole of bacteriochlorophyll a. The observed change upon complete reduction of oxidized membranes with dithionite could be satisfactorily fitted with three cytochrome components having absorption peaks at 553 (cyt c), 558 and 563 nm (cyt b), in relative amounts of 5:1:2. About 20% of total cytochrome 553 were reducible by ascorbate. Menaquinol reduced all of the 553-component, and this reduction was sensitive to stigmatellin, NQNO and antimycin A. The reduction was insensitive to KCN. However, it was transient at low concentrations of menaquinol in the absence of KCN, but permanent in its presence, demonstrating that electron transport into an oxidation pool was blocked. The 563-component was only slightly reduced by menaquinol unless NQNO or antimycin were present. The stimulation of cytochrome 563-reduction by these inhibitors was more pronounced in the presence of ferricyanide. This phenomenon reflects ‘oxidant-induced reduction’ of cytochrome b and demonstrates that a Q-cycle is operative in Chlorobia. Also, sulfide fully reduced cytochrome 553, but more slowly than menaquinol. KCN inhibited in this case, as did stigmatellin, NQNO and antimycin A. NQNO was a better inhibitor than antimycin A. Cytochrome 563 again was hardly reduced unless antimycin A was added. The effect was more difficult to observe with NQNO. This supports the conclusion that sulfide oxidation proceeds via the quinone pool and the cytochrome bc-complex in green sulfur bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029459
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