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  • 1
    Electronic Resource
    Electronic Resource
    Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 169-176 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen-evolving complex ; UV asorbance changes ; EPR signal II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced redox reactions in spinach PS II core particles were investigated with absorbance difference spectroscopy in the UV-region and EPR spectroscopy. In the absence of artificial electron acceptors, electron transport was limited to a single turnover. Addition of the electron acceptors DCBQ and ferricyanide restored the characteristic period-four oscillation in the UV absorbance associated with the S-state cycle, but not the period-two oscillation indicative of the alternating appearance and disappearance of a semiquinone at the QB-site. In contrast to PS II membranes, all active centers were in state S1 after dark adaptation. The absorbance increase associated with the S-state transitions on the first two flashes, attributed to the Z+S1→ZS2 and Z+S2→ZS3 transitions, respectively, had half-times of 95 and 380 μs, similar to those reported for PS II membrane fragments. The decrease due to the Z+S3→ZS0 transition on the third flash had a half-time of 4.5 ms, as in salt-washed PS II membrane fragments. On the fourth flash a small, unresolved, increase of less than 3 μs was observed, which might be due to the Z+S0→ZS1 transition. The deactivation of the higher S-states was unusually fast and occurred within a few seconds and so was the oxidation of S0 to S1 in the dark, which had a half-time of 2–3 min. The same lifetime was found for tyrosine D+, which appeared to be formed within milliseconds after the first flash in about 10% inactive centers and after the third and later flashes by active centers in Z+S3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146416
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  • 2
    Electronic Resource
    Electronic Resource
    Electron transfer in the water-oxidizing complex of Photosystem II (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 125-142 
    Details
    ISSN: 1573-6881
    Keywords: Photosystem II ; water oxidation ; electron transfer ; manganese ; oxygen evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract An overview is presented of secondary electron transfer at the electron donor side of Photosystem II, at which ultimately two water molecules are oxidized to molecular oxygen, and the central role of manganese in catalyzing this process is discussed. A powerful technique for the analysis of manganese redox changes in the water-oxidizing mechanism is the measurement of ultraviolet absorbance changes, induced by single-turnover light flashes on dark-adapted PS II preparations. Various interpretations of these ultraviolet absorbance changes have been proposed. Here it is shown that these changes are due to a single spectral component, which presumably is caused by the oxidation of Mn(III) to Mn(IV), and which oscillates with a sequence +1, +1, +1, −3 during the so-called S0 → S1 → S2 → S3 → S0 redox transitions of the oxygen-evolving complex. This interpretation seems to be consistent with the results obtained with other techniques, such as those on the multiline EPR signal, the intervalence Mn(III)-Mn(IV) transition in the infrared, and EXAFS studies. The dark distribution of the S states and its modification by high pH and by the addition of low concentrations of certain water analogues are discussed. Finally, the patterns of proton release and of electrochromic absorbance changes, possibly reflecting the change of charge in the oxygen-evolving system, are discussed. It is concluded that nonstoichiometric patterns must be considered, and that the net electrical charge of the system probably is the highest in state S2 and the lowest in state S1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762721
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  • 3
    Electronic Resource
    Electronic Resource
    Electroluminescence (1996)
    Springer
    Photosynthesis research 48 (1996), S. 107-116 
    Details
    ISSN: 1573-5079
    Keywords: electric field effect ; luminescence ; membrane potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An overview is presented of research based on the observation by Arnold and Azzi (1971) (Photochem Photobiol 14: 233–240), that an electric field induces charge-recombination luminescence in a suspension of photosynthetic membrane vesicles. The ‘electroluminescence’ signals from Photosystems I and II are discussed in relation to the shape of the vesicles and the membrane potentials generated by the externally applied electric field. The use of the electroluminescence amplitude as a probe to study the kinetics and energetics of charge separation, and of its kinetics to monitor the electric-field induced charge recombination process are reviewed. Currently unresolved issues regarding the emission yield of electroluminescence are briefly discussed and the properties are summarized of the unexplained Photosystem II luminescence which is not sensitive to the membrane potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00041001
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of the redox state of QB on electric field-induced charge recombination in Photosystem II (1996)
    Springer
    Photosynthesis research 48 (1996), S. 197-203 
    Details
    ISSN: 1573-5079
    Keywords: blebs ; charge recombination ; electroluminescence ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Electric field-induced charge recombination in Photosystem II (PS II) was studied in osmotically swollen spinach chloroplasts (‘blebs’) by measurement of the concomitant chlorophyll luminescence emission (electroluminescence). A pronounced dependence on the redox state of the two-electron gate QB was observed and the earlier failure to detect it is explained. The influence of the QB/QB − oscillation on electroluminescence was dependent on the redox state of the oxygen evolving complex; at times around one millisecond after flash illumination a large effect was observed in the states S2 and S3, but not in the state ‘S4’ (actually Z+S3). The presence of the oxidized secondary electron donor, tyrosine Z+, appeared to prevent expression of the QB/QB − effect on electroluminescence, possibly because this effect is primarily due to a shift of the redox equilibrium between Z/Z+ and the oxygen evolving complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00041009
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  • 5
    Electronic Resource
    Electronic Resource
    Absorbance difference spectra of the S-state transitions in Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 323-330 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen evolving complex ; UV absorbance changes ; S-state spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S0 → S1 → S2 → S3 → S0, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S3 state with an inactive state, perhaps related to Ca2+-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 nm, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the S1 → S2 transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation. The spectrum of absorbance changes associated with the S2 → S3 transition was similar to that reported by Lavergne 1991 for PS II membranes. The S0 → S1 transition was associated with a smaller but still substantial absorbance increase in the UV. Differences with the spectra reported by Lavergne 1991 are attributed to electrostatic effects on electron transfer at the acceptor side associated with the S-state dependence of proton release in PS II membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046757
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  • 6
    Electronic Resource
    Electronic Resource
    Rapid and simple isolation of pure photosystem II core and reaction center particles from spinach (1991)
    Springer
    Photosynthesis research 28 (1991), S. 149-153 
    Details
    ISSN: 1573-5079
    Keywords: photosystem II ; core ; reaction center ; isolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pure and active oxygen-evolving PS II core particles containing 35 Chl per reaction center were isolated with 75% yield from spinach PS II membrane fragments by incubation with n-dodecyl-β-D-maltoside and a rapid one step anion-exchange separation. By Triton X-100 treatment on the column these particles could be converted with 55% yield to pure and active PS II reaction center particles, which contained 6 Chl per reaction center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00054128
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