Reconstitution of the Endogenous Plastoquinone Pool in Photosystem II (PS II) Membrane Fragments, Inside-Out-Vesicles, and PS II Core Complexes from Spinach

Abstract

The possibility of reconstituting a functionally competent endogenous plastoquinone pool in photosystem II (PS II) membrane fragments, inside-out-vesicles (ISO-vesicles), and PS II core complexes was analyzed by measuring (i) the characteristic period four oscillation of the oxygen yield due to excitation of dark-adapted samples with a train of short flashes and (ii) laser flash-induced transients of the relative quantum yield of chlorophyll fluorescence. The data obtained revealed that (a) an endogenous pool capacity comparable to that of intact thylakoids can be restored in PS II membrane fragments and ISO-vesicles by a sonication treatment using native plastoquinone-9, (b) a more pronounced oxygen oscillation pattern arises in PS II core complexes after application of the same reconstitution procedure, (c) the extent of the endogenous pool restoration at a ratio of 15 quinone molecules per PS II in the reconstitution assay strongly depends on the nature of the quinone molecule [maximum effects can be only achieved with PQ-9, while at the same concentration ubiquinone-45 (UQ-9) is almost inefficient], and (d) a sonication step is required for stable insertion of PQ-9 into PS II preparations. Measurements of the reconstruction degree as a function of the structure of different quinones with selected properties lead to the conclusion that specific binding domains exist in PS II in addition to the QB site. These domains exhibit a surprisingly high specificity for the type of quinone that can be bound. On the basis of a comparison of the results obtained, the structure of the quinone head group seems to be more important than the large hydrophobic side chain and/or the general lipophilicity of the compound.

Indirect evidence for structural changes coupled with Q−⋅B formation in photosystem II

“…Another important parameter is the PQ pool size in PS II membrane fragments. Its value was found to be 2–3 molecules per PS II [25]so that no limitations occur when the samples are preilluminated by four flashes. Fig.…”

Hybrid bio-photo-electro-chemical cells for solar water splitting

“…4d). The PSII particles are enriched in PSII but contain less PQ and negligible amounts of cyt b 6 f and PSI34, compared with the thylakoids35. An additional explanation to the reduced photocurrent produced by the PSII particles as compared with that produced by intact thylakoids takes into account the reduced amount of PQ pool, which is about 3-fold lower in the PSII particles than in crude thylakoids35.…”

The redox state of the plastoquinone pool directly modulates minimum chlorophyll fluorescence yield in Chlamydomonas reinhardtii

“…The ability of oxidized quinones to quench Chl fluorescence has been suggested in studies using chemically treated membrane fragments [23,24] and thylakoids and reconstituted systems with added non‐native quinones [42,43] and native PQ [8,44,45]. Chl fluorescence quenching by oxidized quinones has been suggested to occur via a transient charge transfer and recombination between Chl and quinone [46,47].…”

“…In darkadapted Arabidopsis thaliana leaves, direct determination of oxidized and reduced PQ indicates that 40% of PQ is reduced [49]. Assuming similar dark aerobic PQ reduction states in A. thaliana and C. reinhardtii , as well as a linear relationship between the amount of oxidized PQ and decrease in fluorescence [44], a total decrease of about 40% in F 0 in the presence of an oxidized PQ pool compared to a reduced PQ pool may be extrapolated.…”