Abstract
Tyrosine Z(YZ) radical has been trapped by illumination at -20 C in Ca-depleted spinach PS II. ELDOR (Electron Electron Double Resonance) was observed at 4.2 K. The observed time profile showed 20 MHz oscillation that corresponds to the distance of 14 A between Mn4 spin center and YZ radical by a point dipole approximation. According to X-ray analysis of cyanobacterial crystal the distances between manganese are about 3 A and the size of cluster is too large for a point dipole approximation.
We have fitted the experimental profile by spin projection and the positions of X-ray analysis for the assumed valence states of each manganese. In the S2-state EXAFS study suggests Mn(III)Mn(IV)3. The best fitted configuration by was found to show that the manganese 1 position takes valence 3, which is closest to YZ. The method was applied to ELDOR for YD-Mn-cluster in the S2 and S0-state.
