High-efficiency oxygen evolution by photosystem II oxygen-evolving complex containing 3Mn per reaction center.

Ca-depleted photosystem II membranes obtained by treatment with acidic buffer do not contain Ca in the MnCaO cluster but contain all extrinsic proteins protecting this cluster (PSII(-Ca/low pH)). However, unlike native photosystem II, Mn cluster in PSII(-Ca/low pH) samples is available for small-sized reductants. Using this property, we investigated the substitution possibility of Mn cation(s) with Fe cation(s) to obtain a chimeric cluster in PSII(-Ca/low pH) samples containing extrinsic proteins.

Ca effects on Fe(II) interactions with Mn-binding sites in Mn-depleted oxygen-evolving complexes of photosystem II and on Fe replacement of Mn in Mn-containing, Ca-depleted complexes.

Fe(II) cations bind with high efficiency and specificity at the high-affinity (HA), Mn-binding site (termed the "blocking effect" since Fe blocks further electron donation to the site) of the oxygen-evolving complex (OEC) in Mn-depleted, photosystem II (PSII) membrane fragments (Semin et al. in Biochemistry 41:5854, 2002). Furthermore, Fe(II) cations can substitute for 1 or 2Mn cations (pH dependent) in Ca-depleted PSII membranes (Semin et al.

pH dependence of photosystem II photoinhibition: relationship with structural transition of oxygen-evolving complex at the pH of thylakoid lumen.

Ca-depleted photosystem II membranes (PSII[-Ca]) do not contain PsbP and PsbQ proteins protecting the MnCaO cluster of the PSII oxygen-evolving complex (OEC). Therefore, the Mn ions in the PSII(-Ca) membranes can be reduced by exogenous bulky reductants or the charged reductant Fe(II). We have recently found that the resistance of Mn ions in the OEC to the Fe(II) action is pH dependent and that this reductant is less effective at pH 5.

Effect of sucrose-bound polynuclear iron oxyhydroxide nanoparticles on the efficiency of electron transport in the photosystem II membranes.

Effect of water-soluble and stable sucrose-bound iron oxyhydroxide nanoparticles [Fe[III] sucrose complex (FSC)] on the efficiency of electron transport in the photosystem II membranes was studied. FSC significantly increases (by a factor 1.5) the rate of light-induced oxygen evolution in the presence of alternative electron acceptor 2,6-dichloro-p-benzoquinone (DCBQ).

Creation of a 3Mn/1Fe cluster in the oxygen-evolving complex of photosystem II and investigation of its functional activity.

Extraction of Mn cations from the oxygen-evolving complex (OEC) of Ca-depleted PSII membranes (PSII[-Ca,4Mn]) by reductants like hydroquinone (HQ) occurs with lower efficiency at acidic pH (2Mn/reaction center [RC] are extracted at pH5.7) than at neutral pH (3Mn/RC are extracted at pH6.5) [Semin et al.

Effect of different methods of Ca extraction from PSII oxygen-evolving complex on the Q oxidation kinetics.

Lumenal extrinsic proteins PsbO, PsbP, and PsbQ of photosystem II (PSII) protect the catalytic cluster MnCaO of oxygen-evolving complex (OEC) from the bulk solution and from soluble compounds in the surrounding medium. Extraction of PsbP and PsbQ proteins by NaCl-washing together with chelator EGTA is followed also by the depletion of Ca cation from OEC. In this study, the effects of PsbP and PsbQ proteins, as well as Ca extraction from OEC on the kinetics of the reduced primary electron acceptor (Q) oxidation, have been studied by fluorescence decay kinetics measurements in PSII membrane fragments.

The extrinsic PsbO protein modulates the oxidation/reduction rate of the exogenous Mn cation at the high-affinity Mn-binding site of Mn-depleted PSII membranes.

The oxidation of exogenous Mn(II) cations at the high-affinity (HA) Mn-binding site in Mn-depleted photosystem II (PSII) membranes with or without the presence of the extrinsic PsbO polypeptide was studied by EPR. The six-lines EPR spectrum of Mn(II) cation disappears in the absence of the PsbO protein in membranes under illumination, but there was no effect when PSII preparations bound the PsbO protein. Our study demonstrates that such effect is determined by significant influence of the PsbO protein on the ratio between the rates of Mn oxidation and reduction at the HA site when the membranes are illuminated.

Correlation between pH dependence of O2 evolution and sensitivity of Mn cations in the oxygen-evolving complex to exogenous reductants.

Effects of pH, Ca(2+), and Cl(-) ions on the extraction of Mn cations from oxygen-evolving complex (OEC) in Ca-depleted photosystem II (PSII(-Ca)) by exogenous reductants hydroquinone (H2Q) and H2O2 were studied. Two of 4 Mn cations are released by H2Q and H2O2 at pHs 5.7, 6.

Production of reactive oxygen species in decoupled, Ca(2+)-depleted PSII and their use in assigning a function to chloride on both sides of PSII.

Extraction of Ca(2+) from the oxygen-evolving complex of photosystem II (PSII) in the absence of a chelator inhibits O2 evolution without significant inhibition of the light-dependent reduction of the exogenous electron acceptor, 2,6-dichlorophenolindophenol (DCPIP) on the reducing side of PSII. The phenomenon is known as "the decoupling effect" (Semin et al. Photosynth Res 98:235-249, 2008).

Rapid degradation of the tetrameric Mn cluster in illuminated, PsbO-depleted photosystem II preparations.

A "decoupling effect" (light-induced electron transport without O2 evolution) was observed in Ca-depleted photosystem II (PSII(-Ca)) membranes, which lack PsbP and PsbQ (Semin et al. (2008) Photosynth. Res.

Decoupling of the processes of molecular oxygen synthesis and electron transport in Ca2+-depleted PSII membranes.

Extraction of Ca(2+) from the O(2)-evolving complex (OEC) of photosystem II (PSII) membranes with 2 M NaCl in the light (PSII(-Ca/NaCl)) results in 90% inhibition of the O(2)-evolution reaction. However, electron transfer from the donor to acceptor side of PSII, measured as the reduction of the exogenous acceptor 2,6-dichlorophenolindophenol (DCIP) under continuous light, is inhibited by only 30%. Thus, calcium extraction from the OEC inhibits the synthesis of molecular O(2) but not the oxidation of a substrate we term X, the source of electrons for DCIP reduction.

Effect of calcium chelators on the formation and oxidation of the slowly relaxing reduced plastoquinone pool in calcium-depleted PSII membranes. Investigation of the F0 yield.

The F(0) fluorescence yield in intact photosystem II (PSII), Ca-depleted PSII (PSII(-Ca/NaCl)), and Mn-depleted PSII membranes was measured before and after dim light treatment (1-2 min), using flash-probe fluorescence and fluorescence induction kinetic measurements. The value of F(0) after the light treatment (F'(0)) was larger than F(0) in dark-adapted PSII membranes and depended on the appearance of the slowly relaxing, reduced plastoquinone pool (t(1/2) = 4 min) formed during preillumination, which was not totally reoxidized before the F'(0) measurement. In PSII(-Ca/NaCl) such a pool also appeared, but the F'(0) yield was even higher than in intact PSII membranes.

Reduction of photosystem I reaction center in DrgA mutant of the cyanobacterium Synechocystis sp. PCC 6803 lacking soluble NAD(P)H:quinone oxidoreductase.

Photoautotrophically grown cells of the cyanobacterium Synechocystis sp. PCC 6803 wild type and the Ins2 mutant carrying an insertion in the drgA gene encoding soluble NAD(P)H:quinone oxidoreductase (NQR) did not differ in the rate of light-induced oxygen evolution and Photosystem I reaction center (P700+) reduction after its oxidation with a white light pulse. In the presence of DCMU, the rate of P700+ reduction was lower in mutant cells than in wild type cells.

pH dependence of the efficiency of binding of iron cations to the donor side of photosystem II.

Light-induced interaction of Fe(II) cations with the donor side of Mn-depleted photosystem II (PS II(-Mn)) results in the binding of iron cations and blocking of the high-affinity (HAZ) Mn-binding site. The pH dependence of the blocking was measured using the diphenylcarbazide/2,6-dichlorophenolindophenol test. The curve of the pH dependence is bell-shaped with pK1 = 5.

Accumulation of ferrous iron in Chlamydomonas reinhardtii. Influence of CO2 and anaerobic induction of the reversible hydrogenase.

The green alga, Chlamydomonas reinhardtii, can photoproduce molecular H(2) via ferredoxin and the reversible [Fe]hydrogenase enzyme under anaerobic conditions. Recently, a novel approach for sustained H(2) gas photoproduction was discovered in cell cultures subjected to S-deprived conditions (A. Melis, L.

[Mossbauer spectroscopy of cells of cyanobacteria Synechocystis sp. PCC 6803 devoid of photosystem I and containing inactive phycobilisomes].

Mossbauer spectra of the psaAB mutant of Synechocystis sp. PPC 6803 devoid of photosystem I grown in a 57Fe-containing medium were measured. The spectrum is a broadened doublet whose size (about 20%) and parameters (isomeric shift delta = 0.

Comparative study of thermal degradation of iron-sulfur proteins in spinach chloroplasts and membranes of thermophilic cyanobacteria: mössbauer spectroscopy.

Mössbauer spectra of chloroplasts isolated from spinach plants grown in a mineral medium enriched with 57Fe and Mössbauer spectra of native membranes of the thermophilic cyanobacterium Synechococcus elongatus contain a broad asymmetric doublet typical of the iron-sulfur proteins of Photosystem (PS) I. Exposure of chloroplasts to temperatures of 20-70 degrees C significantly modifies the central part of the spectra. This spectral change is evidence of decreased magnitude of the quadrupole splitting.

Inorganic Fe2+ formation upon Fe-S protein thermodestruction in the membranes of thermophilic cyanobacteria: Mössbauer spectroscopy study.

A model description of the Mössbauer spectrum (80 K) of native membranes of the thermophilic cyanobacterium Synechococcus elongatus is suggested on the basis of the known values of quadrupole splitting (deltaE(Q)) and isomer shift (deltaFe) for the iron-containing components of the photosynthetic apparatus. Using this approach, we found that heating the membranes at 70-80 K results in a decrease of doublet amplitudes belonging to F(X), F(A), F(B) and ferredoxin and simultaneous formation of a new doublet with deltaE(Q) = 3.10 mm/s and delta-Fe = 1.

Mossbauer spectroscopic study of functional thermal destruction of iron--sulfur proteins in membranes of thermophilic cyanobacteria synechococcus elongatus.

A mathematical model of the Mossbauer spectrum (80K) of native membranes of Synechococcus elongatus was constructed on the basis of values of the quadruple splitting (Delta) and the isomeric shift (delta) of the iron-containing components of the photosynthetic apparatus obtained from the literature. Thermally induced changes in the intensity of the spectral components of membranes and isolated preparations of photosystem (PS) I were studied using this model. It was shown that exposure of membranes to 70-80 degrees C causes a decrease in the intensity of the components related to the FX, FA, and FB centers and surface-located ferredoxins of PS I, an increase in the intensity of the doublets of oxidized iron clusters that are nonspecifically absorbed by the membranes, and formation of a new doublet.

[Creation of Delta mu(H)+ equal to 250 mV on the inner mitochondrial membrane is necessary, but not a sufficient condition for ATP synthesis].

Electron transport in the NADH-ferricyanide and succinate-->O2 chains and ATP synthesis in mitochondria under different incubation conditions have been studied. Ferricyanide which substitutes oxygen as a terminal acceptor provides the generation on the membrane potential, delta microH+, but does not initiate the functioning of the proton cycle. It is suggested that mitochondria can utilize delta microH+ only during the functioning of the redox chain under aerobic conditions.

[The state of lipid peroxidation and of the antioxidant system in the liver and lung microsomes at different periods of sensitization depending on the histamine content].

Histamine impact on lipid peroxidation (LPO) in hepatic and pulmonary microsomes of guinea-pigs sensibilization was studied. It is demonstrated that intensity of chemiluminescence and LPO product content in NADPH-, ascorbat-dependent and spontaneous systems was enhanced in relation to the period of sensibilization process formation and histamine concentration.

[The role of lipid radicals in electron transport and energy transformation].

Data given propose two regimes of lipid radicals and oxygen utilization realized in microsomal and mitochondrial membranes. The first one, lipid peroxidation, i.e.

[Possible participation of a free-radical lipid intermediate in the coupling of oxidation and phosphorylation].

Data shown propose two regimes of lipid radicals and oxygen utilization realized in mitochondrial membranes. The first one--lipid peroxidation, i.e.