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1995 (1)
1Author    K. Burda3-, K. Strzałkab, G. H. Schmid3Requires cookie*
 Title    Europium-and Dysprosium-Ions as Probes for the Study of Calcium Binding Sites in Photosystem II  
 Abstract    Trivalent lanthanide cations are suitable probes for C a2+-binding sites in photosystem II (PS II). PS II membranes prepared from Nicoticinci tabacum, intact and depleted of the extrinsic polypeptides were exposed to lanthanide ions (D y3+ and E u 3+). Small concen­ trations of dysprosium and europium ions enhance oxygen evolution under short saturating flashes. Higher concentrations of the rare earth cations cause the release of the three extrinsic peptides (17, 23 and 33 kDa) and reduce 0 2 yield. The reactivation of the PS II membranes, thus depleted of the 33 kDa subunit, by Ca2+ ions is not possible. Comparing E u 3+ with Dy3+ in this effect shows that E u 3+ is m ore effective than Dy3+, because a lower E u 3+-concentration in comparison to that of Dy3+ inactivates 0 2-evolution. The differences between europium and dysprosium can be explained by their different ionic radius. Our results suggest the existence of two Ca-binding regions: one with a low affinity for calcium would be located on the contact surface of the 23 and 33 kDa proteins and the second one with a high affinity, should be located close to the Mn-cluster and to tyrosine-161 (Z). The more tightly-bound calcium would be responsible for the activity of the PS II system. 
  Reference    Z. Naturforsch. 50c, 220 (1995); received O ctober 6/O ctob er 31 1994 
  Published    1995 
  Keywords    Calcium-Binding Sites, Photosystem II, Tobacco, Oxygen Evolution S-States 
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 TEI-XML for    default:Reihe_C/50/ZNC-1995-50c-0220.pdf 
 Identifier    ZNC-1995-50c-0220 
 Volume    50