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G Renger

Publications and source records attributed to G Renger.

At least 19 recordsLinked to original sources
PubMed2004

Coupling of electron and proton transfer in oxidative water cleavage in photosynthesis.

This minireview addresses questions on the mechanism of oxidative water cleavage with special emphasis on the coupling of electron (ET) and proton transfer (PT) of each individual redox step of the reaction sequence and on the mode of O-O bond formation. The following topics are discussed: (1) the multiphasic kinetics of Y(Z)(ox) formation by P680(+*) originate from three different types of rate limitations: (i) nonadiabatic electron transfer for the "fast" ns reaction, (ii) local "dielectric" relaxation for the "slow" ns reaction, and (iii) "large-scale" proton shift for the micros kinetics; (2) the ET/PT-coupling mode of the individual redox transitions within the water oxidizing complex (WOC) driven by Y(Z)(ox) is assumed to depend on the redox state S(i): the oxidation steps of S(0) and S(1) comprise separate ET and PT pathways while those of S(2) and S(3) take place via proton-coupled electron transfer (PCET) analogous to Jerry Babcock's hydrogen atom abstractor model [Biochim. Biophys. Acta, 1458 (2000) 199]; (3) S(3) is postulated to be a multistate redox level of the WOC with fast dynamic equilibria of both redox isomerism and proton tautomerism. The primary event in the essential O-O bond formation is the population of a state S(3)(P) characterized by an electronic configuration and nuclear geometry that corresponds with a complexed hydrogen peroxide; (4) the peroxidic type S(3)(P) is the entatic state for formation of complexed molecular oxygen through S(3) oxidation by Y(Z)(ox); and (5) the protein matrix itself is proposed to exert catalytic activity by functioning as "PCET director". The WOC is envisaged as a supermolecule that is especially tailored for oxidative water cleavage and acts as a molecular machine.

Electron Transport↗
PubMed2003

Comparative studies on the properties of the extrinsic manganese-stabilizing protein from higher plants and of a synthetic peptide of its C-terminus.

The present study describes a comparative analysis on the fluorescence properties of the manganese-stabilizing protein (MSP), a synthetic peptide corresponding to its C terminus and a 7:1 (molar ratio) mixture of N-acetyl-tyrosine and N-acetyl-tryptophan, respectively, together with reconstitution experiments of oxygen evolution in MSP-depleted photosystem II (PS II) membrane fragments. It is found: (i) at neutral pH, the fluorescence from Trp(241) is strongly diminished in MSP solutions, whereas it highly dominates the overall emission from the C-terminus peptide; (ii) at alkaline pH, the emission of Tyr and Trp is quenched in both, MSP and C-terminus peptide, with increasing pH but the decline curve is shifted by about two pH units towards the alkaline region in MSP; (iii) a drastically different pattern emerges in the 7:1 mixture where the Trp emission even slightly increases at high pH; (iv) the anisotropy of the fluorescence emission is wavelength-independent (310-395 nm) and indicative of one emitter type (Trp) in the C-terminus peptide and of two emitter types (Tyr, Trp) in MSP; and (v) in MSP-depleted PS II membrane fragments the oxygen evolution is restored (up to 85% of untreated control) by rebinding of MSP but not by the C-terminus peptide, however, the presence of the latter diminishes the restoration effect of MSP. A quenching mechanism of Trp fluorescence by a next neighbored tyrosinate in the peptide chain is proposed and the relevance of the C terminus of MSP briefly discussed.

Amino Acid Sequence↗
PubMed2001

Origin and properties of fluorescence emission from the extrinsic 33 kDa manganese stabilizing protein of higher plant water oxidizing complex.

The fluorescence properties of the isolated extrinsic 33 kDa subunit acting as 'manganese stabilizing protein' (MSP) of the water oxidizing complex in photosynthesis was analyzed in buffer solution. Measurements of the emission spectra as a function of excitation wavelength, pH and temperature led to the following results: (a) under all experimental conditions the spectra monitored were found to be the composite of two contributions referred to as '306 nm band' and 'long-wavelength band', (b) the excitation spectra of these two bands closely resemble those of tyrosine and tryptophan in solution, respectively, (c) the spectral shape of the '306 nm band' is virtually independent on pH but its amplitude drastically decreases in the alkaline with a pK of 11.7, (d) the amplitude of the 'long-wavelength' emission band at alkaline pH slightly increases when the pH rises from 7.2 to about 11.3 followed by a sharp decline at higher pH, and (e) the shape of the overall spectrum at pH 7.2 is only slightly changed upon heating to 90 degrees C whereas the amplitude significantly declines. Based on these findings the two distinct fluorescence bands are ascribed to tyrosine(s) ('306 nm band') and the only tryptophan residue W241 of MSP from higher plants ('long-wavelength band') as emitters which are both embedded into a rather hydrophobic environment.

Hydrogen-Ion Concentration↗
PubMed2001

Time-resolved monitoring of flash-induced changes of fluorescence quantum yield and decay of delayed light emission in oxygen-evolving photosynthetic organisms.

The present contribution describes a new experimental setup that permits time-resolved monitoring of the rise kinetics of the relative fluorescence yield, Phi(rel)(t), and simultaneously of the decay of delayed light emission, L(t), induced by strong actinic laser flashes. The results obtained by excitation of dark-adapted samples with a train of eight flashes reveal (a) in suspensions of spinach thylakoids, Phi(rel)(t) exhibits a typical period four oscillation that is characteristic for a dependence on the redox states S(i)() of the water oxidizing complex (WOC), (b) the relative extent of the unresolved "instantaneous" rise to the level (100 ns) at 100 ns and the maximum values of Phi(rel)(t) attained at about 45 s after each actinic flash, (45 s) synchronously oscillate and exhibit the largest values at flash nos. 1 and 5 and minima after flash nos. 2 and 3, (c) opposite effects are observed for the normalized extent of the rise kinetics in the 100 ns to 5 s time domain of relative fluorescence yield, Phi(rel)(5 s) - Phi(rel)(100 ns), i.e., both parameters attain minimum and maximum values after the first/fifth and second/third flash, respectively, and (d) analogous features for the "fast" and "slow" ns-kinetics of the fluorescence rise were observed in suspensions of Chlamydomas reinhardtii cells. A slight phase shift by one flash is ascribed to physiological differences. The applicability of this noninvasive technique to study reactions of photosystem II, especially the reduction kinetics of P680(*)(+) and their dependence on the redox state S(i)() of the WOC, is discussed.

Animals↗
PubMed2001

Mössbauer study of iron centers in D1/D2/Cyt b559 complexes isolated from photosystem II of spinach.

Mössbauer spectroscopy was applied to study the properties of cytochrome b559 (Cyt b559) in isolated D1/D2/Cyt b559 preparations (from spinach) that are completely deprived of non-heme iron. In these samples, all Cyt b559 exists as low-potential form(s) with the iron center attaining the low-spin ferric state in the absence of a strong reductant. The Mössbauer spectra were analyzed using isomer shift and quadrupole splitting parameters below 100 K, gathered from an extrapolation of the temperature dependence of experimental data of photosystem II membrane fragments from spinach. The calculations, based on the Griffith model, lead to the conclusion that the crystal field around the heme iron of Cyt b559 is characterized by a strong rhombic distortion. The g-values obtained are in agreement with recently published EPR results. The use of an extended theoretical approach permits the description of the relaxation changes of the Mössbauer spectra in the temperature region from 5 K to 60 K. It shows that the environment of the heme iron in D1/D2/Cyt b559 is not homogeneous but most likely reflects the existence of two different forms. We assume that factors other than changes of the first coordination sphere are responsible for the drastic negative shift in the redox potential of Cyt b559 that takes place during the isolation procedure of D1/D2/Cyt b559 complexes. Possible implications of these findings are discussed.

Biophysical Phenomena↗
PubMed2001

Effect of D2O and cryosolvents on the redox properties of bacteriochlorophyll dimer and electron transfer processes in Rhodobacter sphaeroides reaction centers.

Effects of environmental changes on the reaction pattern of excitation energy trapping and transformation into the "stable" radical pair P+Q(A)-, have been analyzed in isolated reaction centers of the anoxygenic purple bacterium Rhodobacter sphaeroides. The following results were obtained: (a) replacement of exchangeable protons by deuterons significantly retarded the electron transfer steps of primary charge separation, leading to the radical pair P+I- and of the subsequent reoxidation of I- by the quinone acceptor Q(A) but has virtually no effect on the midpoint potential of P/P+ that was found to be 430+/-20 mV; (b) addition of 70% (v/v) glycerol causes a shift of Em by about 30 mV towards higher values whereas the kinetics of the electron transfer reactions remain almost unaffected; (c) in the presence of the cryoprotectant DMSO, a combined effect arises, i.e. a retardation of the electron transfer kinetics comparable to that induced by H/D exchange and simultaneously an upshift of the Em value to 475+/-20 mV, resembling the action of glycerol. These results are discussed within the framework of effects on the midpoint potential due to the dielectric constant of the medium and changes of the charge distribution in the vicinity of the redox groups and the influence of relaxation processes on electron transfer reactions.

Bacteriochlorophylls↗
PubMed2001

Effect of monochromatic UV-B radiation on electron transfer reactions of Photosystem II.

The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 mW m(-2)) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, DeltaA(325)(t), as an indicator of redox changes in Q(A), and of the relative fluorescence quantum yield, F(t)/F(o), in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 mus) of the 325 nm absorption changes, DeltaA(325), remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 mus kinetics of DeltaA(325) dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl(2), c) the extent of the flash induced rise of the relative fluorescence quantum yield was severely diminished in UV-B treated PS II membrane fragments but the relaxation kinetics remain virtually unaffected. Based on these results the water oxidizing complex (WOC) is inferred to be the primary target of UV-B impairment of PS II while the formation of the 'stable' radical pair P680(+*)Q(A) (-) (*) is almost invariant to this UV-B treatment.

Journal Article↗
PubMed2000

Pigment binding site properties of two photosystem II antenna proteins. A resonance raman investigation.

Two light-harvesting proteins associated with photosystem II of higher plants, namely the major antenna complex LHCIIb and the minor Lhcb4 protein (CP29), have been investigated by resonance Raman spectroscopy. One of the two chlorophylls b and up to five of the six chlorophylls a present in Lhcb4 are shown to adopt similar binding conformations to the (presumably) corresponding molecules in LHCIIb, whereas at least two chlorophylls in the former protein assume unique conformations relative to the bulk complex. The overall conformation of bound xanthophyll molecules is identical in the two antenna proteins, although some small differences are apparent. The pigment binding properties of these two LHCs are discussed, with particular reference to possible structural motifs within this extended family of proteins.

Binding Sites↗
PubMed2000

Delayed fluorescence emitted from light harvesting complex II and photosystem II of higher plants in the 100 ns-5 micros time domain.

This study presents the first report on delayed fluorescence (DF) emitted from spinach thylakoids, D1/D2/Cytb-559 preparations and solubilized light harvesting complex II (LHCII) in the ns time domain after excitation with saturating laser flashes. The use of a new commercially available multichannel plate with rapid gating permitted a sufficient suppression of detector distortions due to the strong prompt fluorescence. The following results were obtained: (a) in dark-adapted thylakoids, the DF amplitudes at 100 ns and 5 micros after each flash of a train of saturating actinic pulses exhibit characteristic period four oscillations of opposite sign: the DF amplitudes at 100 ns oscillate in the same manner as the quantum yield of prompt fluorescence, whereas those at 5 micros resemble the oscillation of the micros kinetics of P680(.) reduction in samples with an intact water oxidizing complex, (b) the quantum yield of total DF emission in the range up to a few micros is estimated to be <10(-4) for thylakoids, (c) the DF of D1/D2/Cytb-559 exhibits a monophasic decay with tau approximately 50 ns, (d) DF emission is also observed in isolated LHCII with biphasic decay kinetics characterized by tau values of 65 ns and about 800 ns, (e) in contrast to thylakoids, the amplitudes of DF in D1/D2/Cytb-559 preparations and solubilized LHCII do not exhibit any oscillation pattern and (f) all spectra of DF from the different sample types are characteristic for emission from the lowest excited singlet state of chlorophyll a. The implications of these findings and problems to be addressed in future research are briefly discussed.

Fluorescence↗
PubMed2000

Is the manganese stabilizing 33 kDa protein of photosystem II attaining a 'natively unfolded' or 'molten globule' structure in solution?

This study compares the properties of the extrinsic 33 kDa subunit acting as 'manganese stabilizing protein' (MSP) of the water oxidizing complex with characteristic features of proteins that are known to attain a 'natively unfolded' or a 'molten globule' structure. The analysis leads to the conclusion that the MSP in solution is most likely a 'molten globule' with well defined compact regions of beta structure. The possible role of these structural peculiarities of MSP in solution for its function as important constituent of the WOC is discussed.

Manganese↗
PubMed2000

Investigation of the plastoquinone pool size and fluorescence quenching in thylakoid membranes and Photosystem II (PS II) membrane fragments.

The efficiency of oxidized endogenous plastoquinone-9 (PQ-9) as a non-photochemical quencher of chlorophyll fluorescence has been analyzed in spinach thylakoids and PS II membrane fragments isolated by Triton X-100 fractionation of grana stacks. The following results were obtained: (a) After subjection of PS II membrane fragments to ultrasonic treatment in the presence of PQ-9, the area over the induction curve of chlorophyll fluorescence owing to actinic cw light increases linearly with the PQ-9/PS II ratio in the reconstitution assay medium; (b) the difference of the maximum fluorescence levels, F(max), of the induction curves, measured in the absence and presence of DCMU, is much more pronounced in PS II membrane fragments than in thylakoids; (c) the ratio F(max)(-DCMU)/F(max)(+DCMU) increases linearly with the content of oxidized PQ-9 that is varied in the thylakoids by reoxidation of the pool after preillumination and in PS II membrane fragments by the PQ-9/PS II ratio in the reconstitution assay; (d) the reconstitution procedure leads to tight binding of PQ-9 to PS II membrane fragments, and PQ-9 cannot be replaced by other quinones; (e) the fluorescence quenching by oxidized PQ-9 persists at low temperatures, and (f) oxidized PQ-9 preferentially affects the F695 of the fluorescence emission spectrum at 77 K. Based on the results of this study the oxidized PQ-9 is inferred to act as a non-photochemical quencher via a static mechanism. Possible implications for the nature of the quenching complex are discussed.

Journal Article↗
PubMed2000

Photoinhibition as a function of the ambient redox potential in Tris-washed PS II membrane fragments.

The mode of photoinhibition as a function of the ambient redox potential (E(ambient)) in suspensions of Tris-washed PS II membrane fragments has been analyzed by monitoring flash-induced absorption changes at 830 nm. It was found: (a) the detectable initial amplitude, DeltaA (830) (total) , as a measure of the capacity to form the 'stable' radical pair, P680(+c) Q (A) (-c) , drastically decreases during a 10 min photoinhibition at E(ambient) values below +350 mV; (b) conversely, the normalized extent of the 18 mus relaxation kinetics, DeltaA (830) (18 mus) as a measure of the electron transfer from Y(Z) to P680(+c) becomes highly susceptible to light stress when E(ambient) exceeds values of about +350 mV; (c) effects of the ambient redox potentials are highly pronounced during light exposure under anaerobic conditions, while much smaller differences arise under aerobic conditions; (d) the extent of damage does not correlate with the total concentration of K(3)[Fe(CN)(6)] and K(4)[Fe(CN)(6)] in the suspension during photoinhibition but rather depends on the E( m )-values; (e) qualitatively similar features are observed when the redox buffer system K(3)[Fe(CN)(6)]/Na(2)S(2)O(4) is replaced by K(2)[IrCl(6)]/Na(2)S(2)O(4); (f) the characteristic E(ambient)-dependence of photoinhibition is observed only under anaerobic conditions. The results are discussed with respect to different redox components that might be involved, including brief comments on a possible role of Cyt b559.

Journal Article↗
PubMed2000

Assignment of the lowest Qy-state and spectral dynamics of the CP29 chlorophyll a/b antenna complex of green plants: a hole-burning study.

Low-temperature absorption, fluorescence and persistent non-photochemical hole-burned spectra are reported for the CP29 chlorophyll (Chl) a/b antenna complex of photosystem II of green plants. The absorption-origin band of the lowest Qy-state lies at 678.2 nm and carries a width of approximately 130 cm-1 that is dominated by inhomogeneous broadening at low temperatures. Its absorption intensity is equivalent to that of one of the six Chl a molecules of CP29. The absence of a significant satellite hole structure produced by hole burning, within the absorption band of the lowest state, indicates that the associated Chl a molecule is weakly coupled to the other Chl and, therefore, that the lowest-energy state is highly localized on a single Chl a molecule. The electron-phonon coupling of the 678.2 nm state is weak with a Huang-Rhys factor S of 0.5 and a peak phonon frequency (omega m) of approximately 20 cm-1. These values give a Stokes shift (2S omega m) in good agreement with the measured positions of the absorption band at 678.2 nm and a fluorescence-origin band at 679.1 nm. Zero-phonon holes associated with the lowest state have a width of approximately 0.05 cm-1 at 4.2 K, corresponding to a total effective dephasing time of approximately 400 ps. The temperature dependence of the zero-phonon holewidth indicates that this time constant is dominated at temperatures below 8 K by pure dephasing/spectral diffusion due to coupling of the optical transition to the glass-like two-level systems of the protein. Zero-phonon hole-widths obtained for the Chl b bands at 638.5 and 650.0 nm, at 4.2 K, lead to lower limits of 900 +/- 150 fs and 4.2 +/- 0.3 ps, respectively, for the Chl b-->Chl a energy-transfer times. Downward energy transfer from the Chl a state(s) at 665.0 nm occurs in 5.3 +/- 0.6 ps at 4.2 K.

Light-Harvesting Protein Complexes↗
PubMed1999

Redox and spectral properties of cytochrome b559 in different preparations of photosystem II.

A detailed analysis of the properties of cytochrome b(559) (Cyt b(559)) in photosystem II (PS II) preparations with different degrees of structural complexity is presented. It reveals that (i) D1-D2-Cyt b(559) complexes either in solubilized form or incorporated into liposomes contain only one type of Cyt b(559) with E(m) values of 60 +/- 5 and 100 +/- 10 mV, respectively, at pH 6.8; (ii) in oxygen-evolving solubilized PS II core complexes Cyt b(559) exists predominantly (>85%) as an LP form with an E(m,7) of 125 +/- 10 mV and a minor fraction with an E(m,7) of -150 +/- 15 mV; (iii) in oxygen-evolving PS II membrane fragments three different redox forms are discernible with E(m) values of 390 +/- 15 mV (HP form), 230 +/- 20 mV (IP form), and 105 +/- 25 mV (LP form) and relative amplitudes of 58, 24, and 18%, respectively, at pH 7.3; (iv) the E(m) values are almost pH-independent between pH 6 and 9.5 in all sample types except D1-D2-Cyt b(559) complexes incorporated into liposomes with a slope of -29 mV/pH unit, when the pH increases from 6 to 9.5 (IP and LP form in PS II membrane fragments possibly within a restricted range from pH 6.5 to 8); (v) at pH >8 the HP Cyt b(559) progressively converts to the IP form with increasing pH; (vi) the reduced-minus-oxidized optical difference spectra of Cyt b(559) are very similar in the lambda range of 360-700 nm for all types except for the HP form which exhibits pronounced differences in the Soret band; and (vii) PS II membrane fragments and core complexes are inferred to contain about two Cyt b(559) hemes per PS II. Possible implications of conformational changes near the heme group and spin state transitions of the iron are discussed.

Chenopodiaceae↗
PubMed1999

Interconversion of low- and high-potential forms of cytochrome b(559) in Tris-washed photosystem II membranes under aerobic and anaerobic conditions.

In this study, the reversible conversion between the high- (HP) and low-potential (LP) forms of Cytb(559) has been analyzed in Tris-washed photosystem II (PSII) enriched membranes. These samples are deprived of the Mn cluster of the water-oxidizing complex (WOC) and the extrinsic regulatory proteins. The results obtained by application of optical and EPR spectroscopy reveal that (i) under aerobic conditions, the vast majority of Cytb(559) exhibits a low midpoint potential, (ii) after removal of O(2) in the dark, a fraction of Cytb(559) is converted to the high-potential form which reaches level of about 25% of the total Cytb(559), (iii) a similar dark transformation of LP --> HP Cytb(559) occurs under reducing conditions (8 mM hydroquinone), (iv) under anaerobic conditions and in the presence of 8 mM hydroquinone, about 60% of the Cytb(559) attains the HP form, (v) the interconversion is reversible with the re-establishment of aerobic conditions, and (vi) aerobic and oxidizing conditions (2 mM ferricyanide or 0.5 mM potassium iridate) induce a decrease of the amount of the HP form, also showing that the conversion is reversible. This reversible interconversion between LP and HP Cytb(559) is not observed in PSII membrane fragments with an intact WOC. On the basis of these findings, the possibility is discussed that the O(2)-dependent conversion of Cytb(559) in PSII complexes lacking a functionally competent WOC is related to a protective role of Cytb(559) in photoinhibition and/or that it is involved in the regulation of the assembly of a competent water-oxidizing complex in PSII.

Aerobiosis↗
PubMed1999

P680(+)* reduction kinetics and redox transition probability of the water oxidizing complex as a function of pH and H/D isotope exchange in spinach thylakoids.

The rise of fluorescence as an indicator for P680(+)* reduction by YZ and the period-four oscillation of oxygen yield induced by a train of saturating flashes were measured in dark-adapted thylakoids as a function of pH in the absence of exogenous electron acceptors. The results reveal that: (i) the average amplitude of the nanosecond kinetics and the average of the maximum fluorescence attained at 100 micros after the flash in the acidic range decrease with decreasing pH; (ii) the oxygen yield exhibits a pronounced period-four oscillation at pH 6.5 and higher damping at both pH 5.0 and pH 8.0; (iii) the probability of misses in the Si-state transitions of the water oxidizing complex is affected characteristically when exchangeable protons are replaced by deuterons [at pH <6.5, the ratio alpha(D)/alpha(H) is larger than 1 whereas at pH >7.0 values of <1 are observed]. The results are discussed within the framework of a combined mechanism for P680(+)* reduction where the nanosecond kinetics reflect an electron transfer coupled with a "rocket-type" proton shift within a hydrogen bridge from YZ to a nearby basic group, X [Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431], and subsequent relaxations within a network of hydrogen bonds. It is concluded that in the acidic region the hydrogen bond between YZ and X (most likely His 190 of polypeptide D1) is interrupted either by direct protonation of X or by conformational changes due to acid-induced Ca2+ release. This gives rise to a decreased P680(+)* reduction by nanosecond kinetics and an increase of dissipative P680(+)* recombination at low pH. A different mechanism is responsible for the almost invariant amplitude of nanosecond kinetics and increase of alpha in the alkaline region.

Chlorophyll↗
PubMed1999

Isolation and characterisation of oxygen evolving thylakoids from the marine prokaryote Prochloron didemni.

The present study describes the first successful attempt to isolate oxygen evolving thylakoids and thylakoid fragments from the marine prokaryote Prochloron didemni, a member of the recently discovered group of prochlorophytes. Oxygen evolving thylakoid membranes and fragments were isolated from seawater suspended cells of Prochloron didemni by passage of the cells through a Yeda press and subsequent differential centrifugation of the broken material. Three fractions were collected at 1000 x g, 5000 x g, and 3000 x g and identified by light microscopy as cells (and their fragments), thylakoids and membrane fragments, respectively. Pigment content, oxygen evolution rate and 77 K fluorescence spectra of these fractions were virtually identical. This finding indicates that the membrane fragments obtained are not enriched in photosystem II. The P680+* reduction kinetics of thylakoid membrane fragments were determined by monitoring flash induced absorption changes at 830 nm and analysing the time course of their decay. The multiphasic relaxation kinetics and their modification by NH2OH were found to be similar to those observed in cyanobacteria and plants. These findings provide an independent line of evidence for the idea of a high conservation of the basic structural and functional pattern of the water oxidising complex in all organisms that perform oxygenic photosynthesis.

Chlorophyll↗