Abstract
Oxygen evolution is carried out in Photosystem II (PSII) supercomplex in higher plant and cyanobacteria. PSII contains primary donor P680, consisted of chlorophylls (Chls). In order to oxidize water, P680+ was required to maintain high redox potential of about +1.2 V. In the early report, CW-ENDOR study showed that 82% of the unpaired electron spin was delocalized on one Chl molecule in P680+ in PSII reaction center (PSII RC). On the other hand, FTIR study shows that positive charge is shared equally on the two Chls.
In this study, we measured Electron Spin Echo Envelope Modulation (ESEEM) spectrum of P680+. The obtained hyperfine constants (hfcs) were 2.7 and 2.0 MHz. The hfcs of 3.18 and 2.95 MHz were obtained in isolated Chl a+. The results indicate that 68-85% of an electron spin delocalized on one Chl in P680+. In addition, we measured the ESEEM spectrum of ChlZ+. Based on these results, we will discuss the electron structure of P680+.
