ELECTRON-SPIN ECHO OF SPIN-POLARIZED RADICAL PAIRS IN INTACT AND QUINONE-RECONSTITUTED PLANT PHOTOSYSTEM-I REACTION CENTERS

Light-induced spin-polarised P700(+)A(1)(-) pairs in intact and quinon e-reconstituted photosystem I reaction centres were studied by electro n spin echo (ESE) spectroscopy. The observed strong ESE envelope modul ation was attributed to magnetic dipolar and exchange interactions in the pairs. The values of these interactions were derived from Fourier- transformed time traces and appeared to be D = - 1.71 +/- 0.05 G and J = 0.010 +/- 0.015 G, respectively. A magnetic field effect on the rad ical pair lifetime induced by microwave pumping was observed. The reco nstituted 2,3-dibromo-1,4-naphthoquinone was shown to be located in th e same (A(1)) site as the native phylloquinone.