PULSED EPR MEASUREMENT OF THE DISTANCE BETWEEN P-680(-DOT) AND Q(A)(-CENTER-DOT) IN PHOTOSYSTEM-II(CENTER)

Out-of-phase electron spin echo envelope modulation (ESEEM) spectrosco py was used to determine the distance between the primary donor radica l cation P-680(+.) and the quinone acceptor radical anion Q(A)(-.) in iron-depleted photosystem II in membrane fragments from spinach that a re deprived of the water oxidizing complex. Furthermore, a lower limit for the distance between the oxidized tyrosine residue Y-Z of polypep tide D1 and Q(A)(-.) could be estimated by a comparison of data gather ed from samples where the electron transfer from Y-Z to P-680(+.) is e ither intact or blocked by preillumination in the presence of NH2OH. ( C) 1997 Federation of European Biochemical Societies.