A WELL RESOLVED ODMR TRIPLET MINUS SINGLET SPECTRUM OF P680 FROM PSIIPARTICLES

An ADMR T-S spectrum of the primary donor (P680) of photosystem II (PS II) was obtained from anaerobically photoreduced particles. The spectr um is the best resolved obtained so far having a main bleaching band a t 684 nm with a linewidth of only 100 cm(-1). The view that this spect rum is produced by native homogeneous P680 unlike those obtained befor e is defended. A small bleaching observed at 678 nm is discussed in te rms of the reaction center structure. One possible interpretation of t he observations is that P680 is a very loose dimer with an exciton spl itting of only 144 cm(-1) corresponding to a dimer center-to-center di stance of roughly 11.5 Angstrom A.