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

ESEEM study of the location of spin-polarized chlorophyll-quinone radical pair in membrane-oriented spinach photosystems I and II complexes

“…This value of D corresponds to a distance between P680 and Q A of 27.4 ± 0.3 A. The obtained distance is consistent with that distance measured for the Fe-depleted PS II, 27.4 ± 0.3 A, by Bittl et al [7] and those for cyanide-treated, Zn-substituted and DBMIB reconstituted PS II particles, about 27 A, in our previous work [16]. Taking into account the determined comparatively large distance between P680 and QA, i.e., 27 A, the exchange interaction could be safely assumed to be zero.…”

“…The first pulse was set to to = 1 µs after the laser flash, in which condition the life times of radical pairs were long enough for measurements of ESEEM at low temperatures [7,16]. A sweep of z was scanned over 150 points with a 16 ns increment from the starting point at r = 96 ns.…”

“…T2 is the transverse relaxation time for four single quantum transitions [25]. The angle 9R is given by e9 and (p the angle between R, for P700+A-1 pair or P680 + Qp pair, and the membrane normal n [16] (see Fig. 1).…”

“…Electron transfer in PS II has been extensively studied by EPR as reviewed in [2] and the distances between several paramagnetic species were determined by pulsed EPR [13,14]. The spin-polarized P680+Q A radical pair signal produced by the laser excitation was sensitively detected as an out-of-phase signal by pulsed EPR [15,16] as was performed in purple bacterial reaction center [17]. Non-Boltzmann distribution of spin states in the radical pair gives a high signal intensity and allows the precise determination of the dipole and exchange interactions.…”

“…The distance between the electronic spins on P680+ and Q, was estimated to be 27.4 A by the ESEEM at room temperature in the cyanobacterial PS II particles in which nonheme Fee that is magnetically coupled to Qq was depleted [15]. In plant PS II, we obtained a distance of 27 A at 80 K in the cyanide-treated, Zn-substituted PS II core particles and in the purified Dl-D2-cytochrome b559-PS II reaction center complex which was reconstituted with an artificial quinone DBMIB (2,5-dibromo-3-methyl-6-isopropyl-1, 4-benzoquinone) in the place of plastoquinone [16]. Pulse EPR measurements on oriented membranes give the orientation of the dipolar interaction axis R, i.e., the axis connecting the two unpaired electron spins with respect to the membrane normal n. In the oriented membranes of oxygenevolving and Mn-depleted PS II, we applied the measurements by "2+1" ESE (electron spin echo) and ELDOR (electron electron double resonance) method to know the locations of redox active tyrosine residues Yo, YZ and manganese atoms that donate electrons to P680.…”