Removal of 33 kDa extrinsic protein specifically stabilizes the S₂QA⁻ charge pair in photosystem II

Removal of the 33 kDa extrinsic protein from photosystem (PS) II membranes resulted in markedly increased stabilization of the S 2 Q A − charge pair as measured by thermoluminescence. The stabilization increase was specific for the S 2 Q A − charge pair and did not require any special herbicide. The effect was fully reversed by reconstitution with the 33 kDa protein, but not at all by high concentrations of Cl − , as opposed to those effects known to be reversed by 200 mM Cl − . The data are interpreted as indicating a structural change of the donor and/or acceptor side of PS II dependent on association with the 33 kDa extrinsic protein.