LOCATION OF D+ AND DISTRIBUTION OF SURFACE-CHARGES IN PHOTOSYSTEM-II

Intramembrane position of D+, the unusually stable tyrosine radical in Photosystem II (PS II), has been estimated by analyzing the effect of an electron-spin relaxing agent dysprosium (Dy) on the microwave power saturation of the EPR signal of D+. It is shown that an estimation with an electrostatically neutral complex of Dy with hydroxyEDTA (HEDTA) gives more reliable information on the structural organization of PS II than that with a charged Dy3+ ion or Dy-EDTA- complex. Distance from D+ to the outer surface of PS II was estimated at 36 Å from the data with Dy-HEDTA. The distance to the inner surface was estimated at 28 Å with the three (33, 24 and 18 kDa) peripheral polypeptides associated or at 20 Å without these polypeptides. By comparison of the effect of Dy-HEDTA with those of Dy3+ and Dy-EDTA-, the inner surface newly exposed after the removal of the 24 and 18 kDa polypeptides is shown to be negatively charged and after the removal of the 33 kDa polypeptide to be positively charged. © 1990.