Abstract
Inhibition of oxygen evolution in photosystem II membrane fragments from pea chloroplasts by washing with Zn 2+ causes appearance of the EPR signal of Mn(H 2O) 6 2+. This Mn 2+ remains associated with the membrane fraction. Release of Mn 2+ into the medium was correlated with the amount of the 23 kDa protein removed from the membrane. This suggests that this protein may function as a ‘gate’ to an aqueous compartment into which Mn 2+ is released. Inhibition by Zn 2+ correlated with the release of 1 Mn 2+ per reaction centre, out of a total stoichiometry of 4 Mn atoms per reaction centre. By comparing the release of Mn following Zn-treatment of NaCI or CaC1 2 washed membranes, it is concluded that the 33 kDa protein is involved in binding of 2 Mn.
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