Effect of extraction and subsequent addition of manganese ions on the photo-oxidation of chlorophyll P₆₈₀ in preparations of photosystem II

The authors have studied the effect of reversible extraction of Mn on the value of the photo-induced changes in absorption (ΔA) associated with the photo-oxidation of chlorophyll P₆₈₀ in oxygen-evolving preparations of photosystem II (p.s.-II) of the pea. It is shown that after complete removal of Mn, the magnitude ΔA increases 7-8 times while on subsequent addition of Mn²⁺ it falls to the initial value, four Mn atoms per reaction centre (r.c.) of p.s.-II sufficing for this reactivation. In the presence of 3 μm MgCl₂ such reactivation requires two Mn²⁺ atoms per 1 r.c. of p.s.-II. The results confirm our earlier conclusion that in the donor part of p.s.-II a four-nuclear manganese complex functions and that two of the four Mn atoms may be replaced by Mg²⁺ or another bivalent metal.