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Inhibition by ethylenediamine tetraacetate and restoration by Mn2+ and Ca2+ of oxygen-evolving activity in Photosystem II preparation from the thermophilic cyanobacterium, Synechococcus sp



Inhibition by ethylenediamine tetraacetate and restoration by Mn2+ and Ca2+ of oxygen-evolving activity in Photosystem II preparation from the thermophilic cyanobacterium, Synechococcus sp



Biochimica et biophysica acta: bioenergetics 806(2): 221-229



The Photosystem II particles capable of evolving oxygen with ferricyanide as an electron acceptor were isolated from -octylglucoside-solubilized thylakoid membranes of the thermophilic cyanobacterium Synechococcus sp. High and steady rates of oxygen evolution were observed only in the presence of 0.5% digitonin and 1 M sucrose. The activity was totally lost when the particles had been treated with 1 mM ethylenediamine tetraacetate for 1 min in a hypotonic medium. The treatment removed two out of four Mn atoms present per the Photosystem II reaction center in the particles. A significant rate of oxygen evolution was restored almost immediately after the addition of 5 mM MnCl2 to the treated particles. The activity was also slowly and partially restored when the treated particles had been incubated with 5 mM CaCl2. MgCl2 was much less effective irrespective of the incubation time. The addition of MnCl2 to the CaCl2-restored particles increased the activity to a level which is significantly larger than the sum of the MnCl2- and the CaCl2-induced increases in the activity. The Mn- and Ca-effects were largely suppressed by the simultaneous addition of CaCl2 and MnCl2, respectively. It is concluded that both Mn2+ and Ca2+ are essential components of the water oxidation of photosynthesis, but the two cations support oxygen evolution through different mechanisms.

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Accession: 016142461

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DOI: 10.1016/0005-2728(85)90099-4


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