The distance between P680 and QA in Photosystem II determined by ESEEM spectroscopy

AbstractLight induced spin-polarized P680+Q−A radical pairs were studied by two pulse electron spin echo envelope modulation (ESEEM) spectroscopy in the cyanide-treated and Zn-substituted Photosystem II core complexes and in the isolated D1-D2-cyt b559 reaction center complexes reconstituted with dibromoisopropyl-p-benzoquinone. The observed strong out-of phase ESEEM signals were identified as those of the P680+Q−A radical pairs based on the time variation of the transient CW EPR spectra. The shapes of ESEEM spectra were attributed to dipolar D and spin exchange J interactions in the radical pairs. The values of D and J were derived from a sine Fourier transformation and the center-to-center distance between P680 and QA was determined to be 27.2±1.0Å for all three preparations