Accessibility of tyrosine Y-Z(.) to exogenous reductants and Mn2+ in various Photosystem II preparations

The reduction of tyrosine Y-Z(.) by benzidine and exogenous Mn2+ was studie d by kinetic EPR experiments in various Photosystem II (PSII) preparations. Using lanthanide treated PSII membranes it was demonstrated that neither t he extrinsic polypeptides (17, 23 and 33 kDa) nor the Mn complex block the accessibility of Y-Z(.) to exogenous reductants, such as benzidine. In addi tion, it was shown that in the presence of the native Mn complex exogenous Mn2+ does not reduce Y-Z(.). (C) 2001 Elsevier Science B.V. All rights rese rved.