Abstract
It has been considered that, during the photoinhibition and repair cycle of PS II, the extrinsic proteins are released from PS II upon photoinhibition and rebind to a newly reconstituted PS II. Under illumination with strong light (4 mE m-2 s-1) of spinach PS II membranes, OEC33 was gradually released from PS II and suffered from some damage, resulting in a smeared band in a silver-stained gel of SDS-PAGE. Among the released OEC33, only a fraction that exhibited the smeared band lost the ability to bind to PS II. The presence of scavengers of superoxides or chelating agents during illumination did not affect the protein release but specifically suppressed the damage. Furthermore, exposure to hydroxyl radicals damaged OEC33 in the same way as observed under strong illumination. These results suggest that hydroxyl radicals generated from superoxides damage OEC33 that has been released from PS II under strong illumination.
