A SELECTIVE HOLE-BURNING METHOD APPLIED TO DETERMINE DISTANCES BETWEEN PARAMAGNETIC SPECIES IN PHOTOSYSTEMS

A method of selective hole burning in EPR spectra was applied to deter mine the distances from a radical to the acceptor quinone-iron in bact erial and plant photosystems. A low amplitude hole burning 180 degrees purse and high amplitude 90 degrees and 90 degrees pulses applied to detect ESE of P870(+) in Rb. Sphaeroides and the distance from the pri mary electron donor P870(+) to the acceptor Q(A)(-)Fe(2+) was determin ed to be 26+/-2 Angstrom from the dipolar broadening of the burned hol e in P870(+) EPR. This result is consistent with that given by X-ray a nalysis and susceptibility measurement. In plant photosystem II the sa me method was applied to the EPR spectrum of tyrosine D+, but the effe ct of crystalline field splitting of Fe2+ ion was taken into considera tion. The effective spin value for the ferrous iron in PS II was found to be 0.8 and the distance between the radical and the non-heme iron was obtained to be 42+/-2 Angstrom.