Biomedical subjects

G Renger

Publications and source records attributed to G Renger.

At least 37 records · Page 2Linked to original sources

PubMed1999

Comparative FTIR analysis of the microenvironment of in cyanide-treated, high pH-treated and iron-depleted photosystem II membrane fragments.

FTIR difference spectra due to light-induced formation were measured in control PS II membrane fragments and in samples where the magnetic interaction with the non-heme iron center in its high-spin Fe2+ state is eliminated by three different methods, i.e., extraction of the non-heme iron center, treatment with cyanide, and incubation at high pH (pH = 11). The results obtained reveal that (i) the most pronounced band at 1479 cm-1 reflecting the C../--O stretching mode of in the semiquinone anion radical remains invariant to "iron depletion" while it shifts by 4 and 2 cm-1 to lower frequencies upon cyanide and high pH treatments, respectively, (ii) peaks observed in the 2600-3000 cm-1 region which arise from Fermi resonance of harmonics and combinations of the imidazole ring modes with the hydrogen-bonding NH stretching vibrations are not affected upon iron depletion but are lost in cyanide and high pH-treated samples, and (iii) all three treatments give rise to some similar changes in the amide I bands of the protein backbones and in imidazole ring modes of the coupled histidine. These results show that the hydrogen-bonding interaction of is virtually unaffected upon non-heme iron depletion; in particular, the strong hydrogen bond between QA and a histidine side chain (most likely His 215 of the D2 subunit) is not changed. In marked contrast, drastic changes take place in the hydrogen bonding between QA and His upon CN- and high pH treatments. The straightforward interpretation is that the hydrogen bond is lost upon these treatments. Despite the striking difference in the effect of hydrogen-bonding interaction, all three treatments lead to similar structural pertubations on the protein conformational changes due to formation and ring vibrations of the coupled histidine side chain. On the basis of the data presented in the study, it is inferred that, concerning the hydrogen bond interaction, the microenvironment of is close to the native state when a suitable iron depletion is performed. Accordingly, the previously reported conclusion on the hydrogen-bonding pattern of in PS II [MacMillan, F., Lendzian, F., Renger, G., and Lubitz, W. (1995) Biochemistry 34, 8144-8156] studied by using iron-depleted preparations most likely reflects the situation in an intact PS II.

Cyanides↗

PubMed1999

The role of hydrogen bonds for the multiphasic P680(+)* reduction by YZ in photosystem II with intact oxyen evolution capacity. Analysis of kinetic H/D isotope exchange effects.

The mechanism of multiphasic P680(+)* reduction by YZ has been analyzed by studying H/D isotope exchange effects on flash-induced changes of 830 nm absorption, DeltaA830(t), and normalized fluorescence yield, F(t)/F0, in dark-adapted thylakoids and PS II membrane fragments from spinach. It was found that (a) the characteristic period four oscillations of the normalized components of DeltaA830(t) relaxation and of F(t)/F0 rise in the nanosecond and microsecond time domain are significantly modified when exchangeable protons are replaced by deuterons; (b) in marked contrast to the normalized steady-state extent of the microsecond kinetics of 830 nm absorption changes which increases only slightly due to H/D exchange (about 10%) the Si state-dependent pattern exhibits marked effects that are most pronounced after the first, fourth, fifth, and eighth flashes; (c) regardless of data evaluation by different fit procedures the results lead to a consistent conclusion, that is, the relative extent of the back reaction between P680(+)*QA-* becomes enhanced in samples suspended in D2O; and (d) this enhancement is dependent on the Si state of the WOC and attains maximum values in S2 and S3, most likely due to a retardation of the "35 micros kinetics" of P680(+)* reduction. In an extension of our previous suggestion on the functional role of hydrogen bonding of YZ by a basic group X (Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425-431), a model is proposed for the origin of the multiphasic P680(+)* reduction by YZ. Two types of different processes are involved: (a) electron transfer in the nanosecond time domain is determined by strength and geometry of the hydrogen bond between the O-H group of YZ and acceptor X, and (b) the microsecond kinetics reflect relaxation processes of a hydrogen bond network giving rise to a shift of the equilibrium P680(+)*YZ <==> P680YZ(OX) toward the right side. The implications of this model are discussed.

Chlorophyll↗

PubMed1999

Determination of the distance between Y(Z)ox* and QA-* in photosystem II by pulsed EPR spectroscopy on light-induced radical pairs.

Out-of-phase electron spin echo envelope modulation (ESEEM) spectroscopy was used to determine the distances within two consecutive radical pair states initiated by a laser flash in photosystem II membrane fragments at pH 11. The distance between the spin density centers of the primary electron donor cation radical, P680+*, and the reduced plastoquinone acceptor, QA-*, has been found to be 27.7+/-0.7 A in agreement with previous results. Near room temperature and at high pH, P680+* is reduced by Y(Z), a redox active tyrosine residue, on a sub-microsecond timescale. As a consequence, the subsequent radical pair state, Y(Z)ox*-QA-*, could be investigated after almost complete reduction of P680+* by Y(Z). The determined dipolar electronic spin-spin coupling within the radical pair Y(Z)ox*QA-* corresponds to a distance of 34+/-1 A between the two molecules.

Electron Spin Resonance Spectroscopy↗

PubMed1999

Quenching of chlorophyll fluorescence by triplets in solubilized light-harvesting complex II (LHCII).

The quenching of chlorophyll fluorescence by triplets in solubilized trimeric light harvesting complexes was analyzed by comparative pump-probe experiments that monitor with weak 2-ns probe pulses the fluorescence yield and changes of optical density, DeltaOD, induced by 2-ns pump pulses. By using a special array for the measurement of the probe fluorescence (Schödel R., F. Hillman, T. Schrötter, K.-D. Irrgang, J. Voight, and G. Biophys. J. 71:3370-3380) the emission caused by the pump pulses could be drastically reduced so that even at highest pump pulse intensities, IP, no significant interference with the signal due to the probe pulse was observed. The data obtained reveal: a) at a fixed time delay of 50 ns between pump and probe pulse the fluorescence yield of the latter drastically decreased with increasing IP, b) the recovery of the fluorescence yield in the microseconds time domain exhibits kinetics which are dependent on IP, c) DeltaOD at 507 nm induced by the pump pulse and monitored by the probe pulse with a delay of 50 ns (reflecting carotenoid triplets) increases with IP without reaching a saturation level at highest IP values, d) an analogous feature is observed for the bleaching at 675 nm but it becomes significant only at very high IP values, e) the relaxation of DeltaOD at 507 nm occurs via a monophasic kinetics at all IP values whereas DeltaOD at 675 nm measured under the same conditions is characterized by a biphasic kinetics with tau values of about 1 microseconds and 7-9 microseconds. The latter corresponds with the monoexponential decay kinetics of DeltaOD at 507 nm. Based on a Stern-Volmer plot, the time-dependent fluorescence quenching is compared with the relaxation kinetics of triplets. It is shown that the fluorescence data can be consistently described by a quenching due to triplets.

Biophysical Phenomena↗

PubMed1999

Spectroscopic characterization of the spinach Lhcb4 protein (CP29), a minor light-harvesting complex of photosystem II.

A spectroscopic characterization is presented of the minor photosystem II chlorophyll a/b-binding protein CP29 (or the Lhcb4 protein) from spinach, prepared by a modified form of a published protocol [Henrysson, T., Schroder, W. P., Spangfort, M. & Akerlund, H.-E. (1989) Biochim. Biophys. Acta 977, 301-308]. The isolation procedure represents a quicker, cheaper means of isolating this minor antenna protein to an equally high level of purity to that published previously. The pigment-binding protein shows similarities to other related light-harvesting complexes (LHCs), including the bulk complex LHCIIb but more particularly another minor antenna protein CP26 (Lhcb5). It is also, in the main, similar to other preparations of CP29, although some significant differences are discussed. In common with CP26, the protein binds about six chlorophyll a and two chlorophyll b molecules. Two chlorophyll b absorption bands are present at 638 and 650 nm and they are somewhat more pronounced than in a recent report [Giuffra, E., Zucchelli, G., Sandonà, D., Croce, R., Cugini, D., Garlaschi, F.M., Bassi, R. & Jennings, R.C. (1997) Biochem. 36, 12984-12993]. The bands give rise to positive and negative linear dichroism, respectively; both show negative CD bands (cf. bands with similar properties at 637 and 650 nm in CP26). Chlorophyll a absorption is dominated by a large contribution at 674 nm which also shows similarities to the major band in LHCIIb and CP26, while (as for CP26) a reduction in absorption around 670 nm is observed relative to the bulk complex. Principal differences from LHCIIb and CP26, and from other CP29 preparations, occur in the carotenoid region.

Circular Dichroism↗

PubMed1998

Correlation between protein flexibility and electron transfer from QA-* to QB in PSII membrane fragments from spinach.

To analyze a possible correlation between the extent of QA-* reoxidation and protein dynamics, fluorometric and Mössbauer spectroscopic measurements were performed in photosystem II membrane fragments from spinach. Numerical evaluation of the flash-induced change of the normalized fluorescence quantum yield revealed that the extent of reoxidation starts to decrease below 275 K and is almost completely suppressed at 230 K. Detailed analyses of Mössbauer spectra measured at different temperatures in 57Fe-enriched material indicate that the onset of fluctuations between conformational substates of the protein matrix occurs also at around 230 K. Based on this correspondence, protein flexibility is inferred to play a key role for QA-* reoxidation in photosystem II. Taking into account the striking similarities with purple bacteria and the latest structural information on these reaction centers [Stowell, M. H. B., McPhillips, T. M., Rees, D. C., Soltis, S. M., Abresch, E., and Feher, G. (1997) Science 276, 812-816], it appears most plausible that also the headgroup of plastoquinone-9 bound to the QB-site in PSII requires a structural reorientation for its reduction to the semiquinone.

Chloroplasts↗

PubMed1998

On the origin of the '35-mus kinetics' of P680(+.) reduction in photosystem II with an intact water oxidising complex.

The origin of the '35-micros kinetics' of P680(+.) reduction in photosystem II (PS II) with an intact water oxidising complex has been analysed by comparative measurements of laser flash induced changes of the 830-nm absorption and the relative quantum yield of chlorophyll (Chl) fluorescence. The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F., Christen, G. and Renger, G. (1997) Photosynth. Res. 51, 231-2421. It was found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted samples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35-micros kinetics under identical excitation conditions are strikingly different with maxima after the 3rd and 5th flash for the 830-nm absorption changes vs. pronounced maxima after the 4th and 8th flash for the rise of the fluorescence yield. The period four oscillations unambiguously show that the '35-micros kinetics' of P680(+.) reduction are characteristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) indicates that in contrast to the ns components of P680(+.) reduction the 35-micros kinetics do not reflect exclusively an electron transfer from Y(Z) to P680(+.). It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680(+.) reduction by Y(Z) and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield.

Chlorophyll↗

PubMed1998

Indirect evidence for structural changes coupled with QB-. formation in photosystem II.

The thermal blockage of QA-. oxidation was analysed in PS II membrane fragments by monitoring flash-induced changes of the relative fluorescence quantum yield as a function of temperature. The results obtained reveal: (a) in dark-adapted samples the fraction of QA-. that is not reoxidised within a time domain of 10 s after the actinic flash increases with lowering the temperature (half-maximum effect at 250-260 K), (b) at low temperatures where QA-. generated in dark-adapted samples remains almost completely reduced, a significant extent of QA-. reoxidation arises when samples are used that were preilluminated at room temperature by one saturating flash followed by rapid freezing before performing the experiment, and (c) the extent of QA-. that is reoxidised at 258 K exhibits a characteristic binary oscillation as a function of the number of preillumination flashes given at room temperature. Based on these data it is inferred that QB and QB-. are located at different equilibrium positions in the QB site. As a consequence the formation of QB-. is coupled with significant structural changes that require sufficient flexibility of the protein matrix. This general feature corresponds with a recently proposed model for the acceptor side reactions of anoxygenic bacteria [Stowell, M.H.B., McPhillips, T.M., Rees, D.C., Soltis, S.M., Abresch, E. and Feher, G., Science 276 (1997) 812-816].

Darkness↗

PubMed1998

Rate of carotenoid triplet formation in solubilized light-harvesting complex II (LHCII) from spinach.

In the present study the rate of triplet transfer from chlorophyll to carotenoids in solubilized LHCII was investigated by flash spectroscopy using laser pulses of approximately 2 ns for both pump and probe. Special attention has been paid to calibration of the experimental setup and to avoid saturation effects. Carotenoid triplets were identified by the pronounced positive peak at approximately 507 nm in the triplet-singlet difference spectra. DeltaOD (507 nm) exhibits a monoexponential relaxation kinetics with characteristic lifetimes of 2-9 micros (depending on the oxygen content) that was found to be independent of the pump pulse intensity. The rise of DeltaOD (507 nm) was resolved via a pump probe technique where an optical delay of up to 20 ns was used. A thorough analysis of these experimental data leads to the conclusion that the kinetics of carotenoid triplet formation in solubilized LHCII is almost entirely limited by the lifetime of the excited singlet state of chlorophyll but neither by the pulse width nor by the rate constant of triplet-triplet transfer. Within the experimental error the rate constant of triplet-triplet transfer from chlorophyll to carotenoids was estimated to be kTT > (0.5 ns)-1. This value exceeds all data reported so far by at least one order of magnitude. The implications of this finding are briefly discussed.

Biophysical Phenomena↗

PubMed1997

Modification of the water oxidizing complex in leaves of the dgd1 mutant of Arabidopsis thaliana deficient in the galactolipid digalactosyldiacylglycerol.

The primary biochemical defect in the genetically well characterized dgd1 mutant of Arabidopsis thaliana causes a 90% reduction in the relative amount of the galactolipid digalactosyldiacylglycerol (DGDG). To study the effect of this DGDG deficiency on photosystem II (PS II), time-resolved transients of laser-flash-induced changes of the relative fluorescence quantum yield Fvar,rel(t) were measured in whole leaves from wild-type and the dgd1 mutant. The results obtained reveal (i) in untreated leaves the decay kinetics of Fvar, rel(t) reflecting QA.- reoxidation by endogenous plastoquinone are very similar in wild-type and the dgd1 mutant at room temperature, (ii) the Arrhenius plot of the temperature dependence of electron transfer from QA.- to QB exhibits a break point at about 19 degrees C in wild-type and about 12 degrees C in the dgd1 mutant, (iii) in leaves treated with DCMU the slow reoxidation of QA.- by the PS II donor side is blocked to a much higher extent in the dgd1 mutant (about 50%) compared to wild-type (about 10%), and iv) the normalized amplitude of Fvar,rel(t = 1 micros) reflecting the percentage of fast P680.+ reduction by YZ exhibits a characteristic period four oscillation in wild-type while this feature is strongly damped in the dgd1 mutant. Presumably, the severe DGDG deficiency is causing the thermal down shift of a lipid phase transition that affects the QA.- reoxidation by QB. Most strikingly, the properties of the WOC are modified as a result of reduced DGDG content. Thus, the lipid DGDG appears to be of structural relevance for the WOC.

Arabidopsis↗

PubMed1997

Pulsed EPR measurement of the distance between P680+. and Q(A)-. in photosystem II.

Out-of-phase electron spin echo envelope modulation (ESEEM) spectroscopy was used to determine the distance between the primary donor radical cation P680+. and the quinone acceptor radical anion Q(A)-. in iron-depleted photosystem II in membrane fragments from spinach that are deprived of the water oxidizing complex. Furthermore, a lower limit for the distance between the oxidized tyrosine residue Y(Z) of polypeptide D1 and Q(A)-. could be estimated by a comparison of data gathered from samples where the electron transfer from Y(Z) to P680+. is either intact or blocked by preillumination in the presence of NH2OH.

Benzoquinones↗

PubMed1997

Analysis of the reaction coordinate of photosynthetic water oxidation by kinetic measurements of 355 nm absorption changes at different temperatures in photosystem II preparations suspended in either H2O or D2O.

Flash-induced absorption changes at 355 nm were measured at different temperatures within the range of 2 degrees C </= theta </= 25 degrees C in dark-adapted PS II core complexes from spinach [O2 evolution rate: 1500 +/- 100 micromol of O2 (mg of Chl)-1 h-1] that were dissolved either in H2O- or in D2O-containing buffer. Comparative measurements were performed at 20 degrees C in H2O- or D2O-containing suspensions of PS II membrane fragments [O2 evolution rate: 600 +/- 40 micromol of O2 (mg of Chl)-1 h-1]. The results obtained reveal the following: (a) The activation energies of the individual redox steps in the water oxidizing complex (WOC) are dependent on the redox state Si with EA(S1-->S2) = 14 kJ/mol, EA(S2-->S3) = 35 kJ/mol, and EA(S3-->-->S0 + O2) = 21 kJ/mol for theta > 11 degrees C, 67 kJ/mol for theta < 11 degrees C in PS II core complexes dissolved in H2O; (b) replacement of exchangeable protons by deuterons causes only minor changes (</=15%) of the activation energies; and (c) the rate constants of these reactions in PS II core complexes are characterized by H/D isotope ratios, ki(H)/ki(D), of 1.6, 2.3, and 1.5 for the transitions S1 --> S2, S2 --> S3, and S3 -->--> S0 + O2, respectively. The corresponding values of PS II membrane fragments are 1.3, 1.3, and 1. 4. Based on these results and corresponding EA data reported in the literature for PS II membrane fragments from spinach [Renger, G., & Hanssum, B. (1992) FEBS Lett. 299, 28-32] and PS II particles from the thermophilic cyanobacterium Synechococcus vulcanus Copeland [Koike, H., Hanssum, B., Inoue, Y., & Renger, G. (1987) Biochim. Biophys. Acta 893, 524-533], the reaction coordinate of the redox sequence in the WOC is inferred to be almost invariant to the evolutionary development from cyanobacteria to higher plants. Furthermore, the rather high activation energy of the S2 --> S3 transition provides evidence for a significant structural change coupled with this reaction. Implications for the mechanism of photosynthetic water oxidation are discussed.

Deuterium Oxide↗

PubMed1997

Quenching of chlorophyll a fluorescence in the aggregates of LHCII: steady state fluorescence and picosecond relaxation kinetics.

The protein composition, steady state and time-resolved fluorescence emission spectra were studied in solubilized and aggregated LHCII complexes, that were prepared according to two different isolation protocols: (1) by fractionation of cation-depleted thylakoid membranes using the non-ionic detergent Triton X-100 according to the procedure of Burke et al. [(1978) Arch. Biochem. Biophys. 187, 252-263] or (2) by solubilization with N-beta-dodecyl maltoside (beta-DM) of photosystem II (PSII) membrane fragments in the presence of cations [Irrgang et al. (1988) Eur. J. Biochem. 178, 207-217]. Based on the analysis of the decay-associated emission spectra measured at 10 and 80 K five long-wavelength chlorophyll species were identified in aggregated LHCII complexes. These five forms are characterized by emission maxima at 681.5, 683, 687, 695, or 702 nm. All of these forms were found in both types of LHCII preparations but the relative amounts and temperature dependency of these species were markedly different in the aggregated LHCII complexes isolated by the two procedures. It was found that these differences cannot be simply explained by effects due to using a less mild detergent as beta-DM or by an ionic influence of Ca2+. Biochemical analysis of the protein composition showed that beta-DM type LHCII consists of all the chlorophyll (Chl)binding proteins belonging to the antenna system of PSII except the CP29 type II gene product (CP29). In contrast, the Triton X-100-solubilized LHCII is highly depleted in CP26 (CP 29 type I gene product) and is contaminated by a variety of unidentified polypeptides. It is proposed that the aggregates of LHCII prepared using Triton X-100 acquire specific spectral and kinetic features due to interaction between the bulk of LHCII subunits and minor protein(s).

Calcium↗

PubMed1997

S(-3) state of the water oxidase in photosystem II.

The effect of the reductant hydrazine on the flash-induced oxygen oscillation patterns of spinach thylakoids was used to characterize a new super-reduced redox state of the water oxidase in photosystem II. The formation of a discrete S(-3) state is evident from the shift of the first maximum of oxygen evolution from the 3rd flash through the 5th flash to the 7th flash during a 90 min incubation of dark-adapted thylakoids with 10 mM hydrazine sulfate at pH 6.8 on ice. A distinct period four oscillation with further maxima on the 11th and 15th flashes is still observed at this stage of the incubation. The data analysis within the framework of an extended Kok model reveals that a S(-3) state population of almost 50% can be achieved by this treatment. A prolonged incubation of the S(-3) sample with 10 mM hydrazine (and even 100 mM) does not lead to a further shift of the first maximum toward the 9th flash that could reflect the formation of the S(-5) state. Instead, a slow oxidation of S(-3) to S(-2) takes place by an as yet unidentified electron acceptor. A consistent simulation of all the measured oxygen oscillation patterns of this study could, however, only be achieved by including the formal redox states S(-4) and S(-5) in the fits (S(-4) + S(-5) up to 35%). The implications of these findings for the oxidation states of the manganese in the tetranuclear cluster of the water oxidase are discussed.

Hydrazines↗

PubMed1997

Analysis of pH-induced structural changes of the isolated extrinsic 33 kilodalton protein of photosystem II.

Structural properties of the isolated extrinsic regulatory 33 kDa protein of the water-oxidizing complex were analyzed at different pH values. It was found that (a) titrations of the buffer capacity reveal a characteristic hysteresis effect that is unique for the 33 kDa subunit and is not observed for the other extrinsic proteins, (b) changes of the emission from the fluorescence probe 1,8-ANS are indicative of an increased accessibility of the hydrophobic core of the 33 kDa protein to the dye at lower pH, (c) the near-UV circular dichroism spectrum of the polypeptide is altered owing to a pH decrease from 6.8 to 3.8 and becomes drastically changed at pH 2.8, and (d) the content of secondary structure elements remains virtually constant in the range 3.8 < pH < 6.8, with the following values gathered from far-UV CD spectra: approximately 8% alpha-helix, approximately 33% beta-strand, approximately 15% turns, and approximately 44% random coil. Further acidification down to pH 2.8 gives rise to a decreased alpha-helix and increased beta-strand and random coil content. A theoretical model [Ptitsyn, O., & Finkelstein, A. (1983) Biopolymers 2, 15-22] was used to predict the probability and location of secondary structure elements within the protein sequence. On the basis of these calculations, an extended hydrophobic beta-sheet domain could exist in the center of the protein and an alpha-helix in the C-terminal region. From these data, the 33 kDa protein is inferred to change its tertiary structure in vitro upon acidification of the aqueous environment. Possible implications of these features are discussed.

Anilino Naphthalenesulfonates↗

PubMed1997

Kinetics of S2 and S3 reduction by tyrosine Y(D) and other endogenous donors as a function of temperature in spinach PS II membrane fragments with a reconstituted plastoquinone pool.

The characteristic period four oscillation patterns of oxygen evolution induced by a train of single-turnover flashes were measured as a function of temperature in dark-adapted photosystem II (PS II) membrane fragments that were reconstituted with native plastoquinone-9 (PQ-9) by a recently developed procedure [Kurreck, J., Seeliger, A. G., Reifarth, F., Karge, M., & Renger, G. (1995) Biochemistry 34, 15721-15731]. The following results were obtained: (a) within the range 0-35 degrees C, the probabilities of misses (alpha) and double-hits (beta) and the dark population of redox state S1 exhibit similar dependencies on the temperature; (b) below a characteristic temperature theta(c) these parameters remain virtually independent of temperature, above theta(c) (theta(c) = 20 degrees C for alpha and beta; theta(c) = 30 degrees C for S1) the values of alpha and beta increase whereas S1 decreases; and (c) the dark decay of S2 and S3 via fast and slow kinetics owing to reduction of the water oxidase by Y(D) and other endogenous electron donor(s), respectively, exhibits comparatively strong temperature dependencies with the following activation energies: E(A)(S2(fast)) = 60 +/- 10 kJ/mol, EA(S3(fast)) = 55 +/- 10 kJ/mol, E(A)(S2(slow)) = 80 +/- 5 kJ/mol, and E(A)(S3(slow)) = 75 +/- 5 kJ/mol. These values of PQ-9 reconstituted PS II membrane fragments are very similar to those that were previously reported for thylakoids [Messinger, J., Schröder, W. P., & Renger, G. (1993) Biochemistry 32, 7658-7668]. These findings reveal that the reaction coordinates of feeding electrons by endogenous electron donors into the water oxidizing complex (WOC) that attains the redox states S2 and S3 is virtually invariant to Triton X-100 treatment used in the isolation procedure of PS II membrane fragments from thylakoids. Implications of these findings are discussed.

Cell Membrane↗

PubMed1997

Highly purified D1/D2/cyt b559 preparations from spinach do not contain the non-heme iron center.

57Fe enriched D1/D2/cyt b559 preparations were isolated from spinach grown hydroponically on a 57Fe containing medium. In terms of polypeptide and pigment composition these samples are of high purity and functional integrity of P680. Mössbauer spectra measured in D1/D2/cyt b559 complexes revealed that these preparations are completely deprived of the non-heme iron center. Possible implications of this finding are discussed for the electron transfer from Pheo-. to exogenous electron acceptors.

Cytochrome b Group↗

PubMed1996

A null mutant of Synechococcus sp. PCC7942 deficient in the sulfolipid sulfoquinovosyl diacylglycerol.

The sulfolipid 6-sulfo-alpha-D-quinovosyldiacylglycerol is associated with the thylakoid membranes of many photosynthetic organisms. Previously, genes involved in sulfolipid biosynthesis have been characterized only in the purple bacterium Rhodobacter sphaeroides. Unlike plants and cyanobacteria, photosynthesis in this bacterium is anoxygenic due to the lack of a water splitting photosystem II. To test the function of sulfolipid in an organism with oxygenic photosynthesis, we isolated and inactivated a sulfolipid gene of the cyanobacterium Synechococcus sp. PCC7942. Extensive analysis of the sulfolipid-deficient null mutant revealed subtle changes in photosynthesis related biochemistry of O2. In addition, a slight increase in the variable room temperature chlorophyll fluorescence yield was observed. Regardless of these changes, it seems unlikely that sulfolipid is an essential constituent of a functional competent water oxidase or the core antenna complex of photosystem II. However, reduced growth of the mutant under phosphate-limiting conditions supports the hypothesis that sulfolipid acts as a surrogate for anionic phospholipids under phosphate-limiting growth conditions.

Amino Acid Sequence↗