Phosphatidylglycerol effect on oxygen-evolving activity in Ca2+-depleted photosystem II

The effect of anionic phosphatidylglycerol (PG) on oxygen evolution in a photosystem II (PS II ) particle depleted of Ca2+ (designated dCaPSII ) has been investigated. The major finding is the observation of a new role of PG in the PSII function. That is, PG restores nearly the lost oxygen evolution in dcaPS II particle owing to Ca2+ depletion to the levels in intact PS II. Furthermore, there is a stimulation of oxygen-evolving activity in the dCaPSII complexed with PG in the presence of exogenous CaCl2, which PG enhances increasingly oxygen evolution with increasing CaCl2 concentration. It is suggested that PG-induced oxygen evolution recovery of dCa PS II particle results from resumption of normal structure in protein by PG effect, whereas the enhancement of oxygen evolution in complex subject to CaCl2 is ascribed to the optimization of such a structure due to coordination complex formation of Ca2+ ions with PG.