The role of chloride ion on the photoreactivation of the oxygen-evolving center of tris-washed, 2,6-dichlorophenol indophenol-treated grana.

Chloride ion is found to be an essential factor in photoreactivation of the oxygen-evolving center. Tris-washed, 2,6-dichlorophenol indophenol-treated grana are low in both Mn content and oxygen-evolving activity. These grana can restore high oxygen-evolving activity, however, by incorporating Mn2+ ion under weak light in the presence of chloride and calcium ions with dithiothreitol. This restoration is called photoreactivation. When chloride ion is omitted from the medium for the photoreactivation, the recovery of oxygen-evolving activity is inhibited. Other anions, such as bromide and nitrate anions, could also mediate the reactivation; but, anions of weak acids or polyvalent strong acids were not effective. Chloride ion is also required in the light-induced H+ and Mn2+ uptake of these grana, which are essential partial reactions for the reactivation. It is therefore concluded that chloride ion plays an important role in the photoreactivation.