Voltage changes involving photosystem II quinone–iron complex turnover

Abstract

An electrometrical technique was used to investigate proton-coupled electron transfer between the primary plastoquinone acceptor Q (A) (-) and the oxidized non-heme iron Fe(3+) on the acceptor side of photosystem II core particles incorporated into phospholipid vesicles. The sign of the transmembrane electric potential difference Deltapsi (negative charging of the proteoliposome interior) indicates that the iron-quinone complex faces the interior surface of the proteoliposome membrane. Preoxidation of the non-heme iron was achieved by addition of potassium ferricyanide entrapped into proteoliposomes. Besides the fast unresolvable kinetic phase (tau approximately 0.1 micro s) of Deltapsi generation related to electron transfer between the redox-active tyrosine Y(Z) and Q(A), an additional phase in the submillisecond time domain (tau approximately 0.1 ms at 23 degrees C, pH 7.0) and relative amplitude approximately 20% of the amplitude of the fast phase was observed under exposure to the first flash. This phase was absent under the second laser flash, as well as upon the first flash in the presence of DCMU, an inhibitor of electron transfer between Q(A) and the secondary quinone Q(B). The rate of the additional electrogenic phase is decreased by about one-half in the presence of D(2)O and is reduced with the temperature decrease. On the basis of the above observations we suggest that the submillisecond electrogenic reaction induced by the first flash is due to the vectorial transfer of a proton from external aqueous phase to an amino acid residue(s) in the vicinity of the non-heme iron. The possible role of the non-heme iron in cyclic electron transfer in photosystem II complex is discussed.

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

“…The 5th flash mainly induced the S 1 →S 2 transition. It is similar to the 1st flash, but without possible contribution from elec tron transfer to the non heme iron located between quinones [19,25]. Therefore, the difference between kinetic traces induced by the 2nd and 5th flashes (Fig.…”

“…2, c and d). Under these conditions, proton uptake on the acceptor side of PS 2 did not occur [25], and it produces the highest yield of the photoassembly ( [31] and references therein).…”

“…Apo WOC PS 2 core complexes were reconstituted into phospholipid (L α phosphatidylcholine, type II S; Sigma, USA) vesicles as described in [25]. Phospholipid suspension in 50 mM HEPES HCl buffer (pH 7.5) con taining 0.8% (w/v) n octyl β D glucopyranoside (Sigma) was sonicated until clarity.…”

“…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]. The maximum ampli tude fast phase (the rise time is shorter than the time resolution of the experimental setup (~100 ns)) corre sponds to charge separation in PS 2 RC between P 680 and Q A and subsequent P + 680 reduction by electron transfer from redox active tyrosine Y Z (Y • Z Q A − ) [22].…”

Electrogenic reactions and dielectric properties of photosystem II

“…A variety of approaches were developed to monitor electrical events associated with the light-induced electron transfer in the photosynthetic pigment-protein complexes . The photovoltage related to the electron transfer reactions in PS II RC was measured using the lightgradient method in PS II-membrane systems (Witt and Zikler 1973;Fowler and Kok 1974;Graber and Trissl 1981;Trissl et al 1987;Leibl et al 1989;Trissl and Leibl 1989), and using oriented PS II membranes (Pokorny et al 1994) in PS II core complexes oriented in phospholipid monolayers attached to a Teflon support (Hook and Brzezinski 1994), in liposome-reconstituted PS II core complexes associated with lipid-impregnated collodion film (Mamedov et al 1995;Haumann et al 1997;Mamedov et al 2006;Semenov et al 2006), by electroluminescence in swollen thylakoids (Vos et al 1991;de Wijn et al 2001) and by electrochromic absorption changes of pigments in thylakoids (Schliephake et al 1968;Witt et al 1968;Vredenberg 1981;Haumann et al 1997).…”