Accessibility of tyrosine Y(.)(Z) to exogenous reductants and Mn(2+) in various Photosystem II preparations

The reduction of tyrosine Y(.)(Z) by benzidine and exogenous Mn(2+) was studied by kinetic EPR experiments in various Photosystem II (PSII) preparations. Using lanthanide treated PSII membranes it was demonstrated that neither the extrinsic polypeptides (17, 23 and 33 kDa) nor the Mn complex block the accessibility of Y(.)(Z) to exogenous reductants, such as benzidine. In addition, it was shown that in the presence of the native Mn complex exogenous Mn(2+) does not reduce Y(.)(Z).