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  • 1985-1989  (2)
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  • 1
    ISSN: 1573-5079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Oxygen evolution and reduction kinetics of the photooxidized Chl-aII + have been measured in oxygen-evolving complexes from the thermophilic cyanobacterium Synechococcus sp. 1. Incubation of PS II particles with acetate resulted in an inhibition of oxygen evolution and a retardation of the Chl-aII +=reduction kinetics from the nanosecond range to the microsecond range, indicating a modification of the donor side of photosystem II (PS II). 2. After the first two flashes given to a dark-adapted, acetate treated sample, Chl-aII + was re-reduced with a half-life time of 160 μs by a component of the donor side of PS II. Under repetitive excitation Chl-aII + was re-reduced in 500 μs by electron back reaction from the primary acceptor QA - (X-320-). Obviously, in the presence of acetate only two electrons are available from the donor side. 3. Both oxygen evolution and nanosecond reduction kinetics of Chl-aII + were restored to the control level when acetate was removed. 4. The results indicate a tight coupling between O2 evolution and nanosecond reduction kinetics of Chl-aII +. 5. The reversible inhibition is probably due to a replacement of Cl- by acetate within the water splitting enzyme. 6. Due to its strongly retarded kinetics, the reversibly modified system may facilitate investigations of the mechanism of the donor side.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reaction sequence between the primary electron acceptor, the oxidized Chlorophyll-aII, and the terminal electron donor, the water splitting enzyme system S, is being described in the range from nanoseconds to milliseconds. For the cleavage of water Chlorophyll-aII + extracts four electrons in four turnovers from the enzyme system S responsible for the water oxidation. For each extraction the electron is moved step by step along the chain that connects the Chlorophyll-aII center with that of S. Beginning with the transfer from the immediate donor, D1, to Chl-aII +, the subsequent transfer from D2 to D1 + ends in the electron transfer from S to D2 +. This final act establishes in S the oxidizing equivalent, probably in the form of oxidized manganese. Coupled with these acts is an intrinsic proton release and a surplus charge formation. After the generation of the 4th oxidizing equivalent in a concerted final action the evolution of O2 from water takes place. Correlations between the events are described quantitatively.
    Type of Medium: Electronic Resource
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