Relative positions of electron transfer components in Photosystem II studied by ‘2+1’ pulsed electron paramagnetic resonance: YD and QA

AbstractA ‘2+1’ electron spin echo (ESE) method, to measure the dipole interaction between paramagnetic centers directly, has been applied to determine the orientation of the radius-vector RD–Q (YD to QA) in a membrane oriented Fe2+-depleted preparation of Photosystem II. Using the distance of RD–Q=38.5±0.8 Å determined for the non-oriented membranes, the angle between RD–Q and the membrane normal n was determined to be θ0=13.0±4.0°. The distance and angle of another related pair of radicals, RP680–D, were suggested to be 20 Å and 42°, respectively, based on the above data and ESEEM of the P680+QA− in the oriented membranes