Effect of redox mediators on the flash-induced membrane potential generation in Mn-depleted photosystem II core particles

Abstract

An electrometrical technique was used to investigate flash-induced electron transfer reactions between Mn-depleted spinach photosystem II core particles incorporated into liposomes and redox mediators. Besides the fast increase in the transmembrane electric potential difference associated with electron transfer between the redox active tyrosine (Y(Z)) and the primary quinone acceptor Q(A,) an additional electrogenic phase was observed in the presence of N,N,N'N'-tetramethyl-p-phenylenediamine and 2,6-dichlorophenol-indophenol. The latter phase is attributed to vectorial electron transfer from the redox dye(s) to the protein-embedded Y(Z). The data obtained suggest an electrically isolated location of the Y(Z) from the external water phase.

Electrogenic reactions and dielectric properties of photosystem II

“…as an electron donor, and the voltage changes are due to the vectorial electron transfer from the protein-water boundary to Y Z (Gopta et al 2008). This finding implies an electrically isolated location of the Y Z within the protein molecule.…”

“…Therefore, we use only the data for the protein regions between cyt c 559 (heme 1 or h 1 ) and P 960 , as well as between P 960 and Q A , where the average dielectric constant values of 10 and 3 were obtained, respectively. Figure 4c shows that the polarity gradually increases between P and h 1 , so that the The distances along the axis normal to the membrane plane are given according to the X-ray data (Deisenhofer et al 1985) b Relative contributions of partial reactions to the overall electrogenesis were obtained in (Dracheva et al 1988) and (Deprez et al 1986) a The distances along the axis normal to the membrane plane are given according to the X-ray data (Loll et al 2005) b Relative contributions of partial reactions to the overall electrogenesis were obtained in (Haumann et al 1997;Semenov et al 2006;Gopta et al 2008) Photosynth Res (2008) 98:121-130 127 average e value of 10 for this protein region implies that the local dielectric permittivity around heme 1 amounts to *20. Because of the non-planar geometry of the subunit C, the surrounding water solution could largely contribute to this figure of effective permittivity.…”

“…Here and in other figures, arrows indicate laser flashes. The curves 1 and 2 were taken fromGopta et al (2008); the curve 3 was not earlier…”

Vectorial charge transfer reactions on the donor side of manganese-depleted and reconstituted photosystem 2 core complexes

“…To extract Mn, Ca, and extrinsic proteins, PS 2 core complexes were treated with 0.8 M Tris (pH 8.3) buffer for 30 min [24].…”

“…Figure 1 shows electrometrically detected voltage transients induced by the 1st laser flash in dark adapted liposome reconstituted Mn depleted and Mn reconsti tuted (+Mn) core particles. The negative sign of ∆Ψ indicates that the donor side of the enzyme is located at the external surface of the proteoliposomal membrane [21,24]. The lack of membrane impermeable sodium dithionite effect on the amplitude of the voltage transient indicates a highly asymmetric orientation of PS 2 core complexes in the liposomes (~90% of the complexes are facing donor side outside) [25].…”