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

Abstract

Light-induced spin-polarized radical pairs, P700'A-j in spinach photosystem (PS) I particles and P680'Qp in Zn-substituted PS II core complexes, in oriented membranes were studied by pulsed electron paramagnetic resonance (EPR). Based on the determined distance of 25.2 ± 0.2 A between P700 and A" the angular dependence of the spin-polarized electron spin echo envelope modulation (ESEEM) spectra on the magnetic field suggests that the angle between RPlop_A , the radiusvector connecting P700 and A" and the membrane normal n was 24 ± 4° in PS I particles. Obtained angle and distance of P700-A, axis suggested Q K side in the molecular geometry of cofactors presented in a recent X-ray crystallography of cyanobacterial PS I reaction center to be an active branch of electron transfer. The distance between P680 and Q A was determined to be 27.4 ± 0.3 A for a nonoriented PS II. The angle between RP680_Qp, the radius-vector connecting P680 and Q A , and n was determined to be 21 ± 5°. The angle of P680-QA axis was close to that of 20° of P870-QA axis reported in X-ray analysis of the purple bacterial reaction center crystal.

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“…Figure 7 illustrates the relative positions of the electron transfer components in PS II complex, based on the results obtained from the present and previously reported ESEEM [27] and PELDOR studies [17]. The relative positions of Y Z , Y D and Q A in PS II can be unambiguously determined.…”

Three-dimensional structure of electron transfer components in photosystem II: “2 + 1” ESE of chlorophyll Z and tyrosine D

“…They are 39 A and 13° for YD-QA pair [31], 29 A and 100° for Y0-Y, 27 A and 110° for YD-Mn (the S 2 -state multiline) [28] as determined by ELDOR method. 27 A and 21° for P680-Q A were determined by means of spin polarized radical pair ESEEM [32]. The accuracies in distances are within 0.5-1 A, while those in angles are in 4-5°.…”

Long-range distance determinations in biomacromolecules by EPR spectroscopy

“…Interestingly, the latter study was performed at physiological temperatures. Low temperature measurements on oriented membranes revealed an angle of 21° between the dipolar vector and the membrane normal (Yoshii et al 1999a). Out-of-phase echo measurements have also been applied to acquire the distance between Q A −● and Y Z +● (Zech et al 1999).…”