THE DISTANCES FROM TYROSINE-D TO REDOX-ACTIVE COMPONENTS ON THE DONORSIDE OF PHOTOSYSTEM-II DETERMINED BY PULSED ELECTRON-ELECTRON DOUBLE-RESONANCE

A pulsed electron-electron double resonance (ELDOR) method was applied to measure the dipole interactions between paramagnetic species on th e donor side of Photosystem II. The distance between the Mn cluster an d the redox-active tyrosine residue Y-D was determined to be 27 +/- 0. 2 Angstrom in the S-2 state of the oxygen-evolving Photosystem II. In Ca2+-depleted preparations the same distance was obtained from the mea surement of the modified multiline signal. The distance between Y-D an d the paramagnetic species giving. rise to the split S-3 signal was fo und to be 30 +/- 0.2 Angstrom.