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1.
Neil V. Blough  Kenneth Sauer 《BBA》1984,767(2):377-381
The ability of salts to inhibit the O2-evolution activity of PS II preparations is shown to parallel closely the Hofmeister series, suggesting that inhibition is related to the solubility of the 16, 24 and 33 kDa proteins in these salt solutions. An examination of the effect of salt inactivation on the low temperature multiline EPR signal indicates that the release of either the 16 and 24 kDa proteins, or additionally the 33 kDa protein blocks or greatly reduces the efficiency of the advancement of the water-splitting complex to the S2-state; under some conditions, this inhibition is reversible.  相似文献   

2.
Exposure of Photosystem II (PS II) membrane particles from spinach to a temperature of 47 °C caused the rapid release of the 18 kDa protein in parallel to inactivation of oxygen evolution. Previously, it has been suggested that the first heat-jump response involves rapid Ca release from the Mn complex of O2-evolution, followed by the slower release of (2 + 2) MnII ions [Pospisil P et al. (2003) Biophys J 84: 1370–1386]. Here, the predicted biphasic MnII release to the bulk was verified by atomic absorption spectroscopy (AAS). Analysis of laser flash-induced delayed fluorescence transients suggests that the loss of the essential Ca ion from the Mn4Ca complex in the dark is due to the loss of the 18 kDa protein. The S2-state multiline EPR signal of the Mn complex was still generated in heat-treated PS II presumably lacking Ca, but retaining four Mn ions.Dedicated to Professor Norio Murata on the occasion of his retirement  相似文献   

3.
A new binding site for anions which inhibit the water oxidizing complex (WOC) of Photosystem II in spinach has been identified. Anions which bind to this site inhibit the flash-induced S2/S0 catalase reaction (2H2O22H2O+O2) of the WOC by displacing hydrogen peroxide. Using a mass spectrometer and gas permeable membrane to detect the 32O2 product, the yield and lifetime of the active state of the flash-induced catalase (to be referred to simply as flash-catalase) reaction were measured after forming the S2 or S0-states by a short flash. The increase in flash-catalase activity with H2O2 concentration exhibits a Km=10–20 mM, and originates from an increase in the lifetime by 20-fold of the active state. The increased lifetime in the presence of peroxide is ascribed to formation of the long-lived S0-state at the expense of the unstable S2-state. The anion inhibition site differs from the chloride site involved in stimulating the photolytic water oxidation reaction (2H2OO2+4e-+4H+). Whereas water oxidation requires Cl- and is inhibited with increasing effectiveness by F-CN-N3 -, the flash-catalase reaction is weakly inhibited by Cl-, and with increasing effectiveness by F-CN-, N3 -. Unlike water oxidation, chloride is unable to suppress or reverse inhibition of the flash-catalase reaction caused by these anions. The inhibitor effectiveness correlates with the pKa of the conjugate acid, suggesting that the protonated species may be the active inhibitor. The reduced activity arises from a shortening of the lifetime of the flash-induced catalase active state by 3–10 fold owing to stronger anion binding in the flash-induced states, S2 and S0, than in the dark S-states, S1 and S-1. To account for the paradoxical result that higher anion concentrations are required to inhibit at lower H2O2 concentrations, where S2 forms initially after the flash, than at higher H2O2 concentrations, where S0 forms initially after the flash, stronger anion binding to the S0-state than to the S2-state is proposed. A kinetic model is given which accounts for these equilibria with anions and H2O2. The rate constant for the formation/release of O2 by reduction of S2 in the WOC is <0.4 s-1.Abbreviations ADRY acceleration of the deactivation reactions of the water splitting enzyme system Y - BTP bis [tris(hydroxymethyl)methylamino]-propane - CCCP carbonylcyanide m-chlorophenylhyrazone - DCBQ 2,5-dichlorobenzoquinone - DMBQ 2,3-dimethylbenzoquinone - WOC water oxidizing complex  相似文献   

4.
The manganese complex (Mn4) which is responsible for water oxidation in photosystem II is EPR detectable in the S2-state, one of the five redox states of the enzyme cycle. The S2-state is observable at 10?K either as an EPR multiline signal (spin S?=?1/2) or as a signal at g?=?4.1 (spin S?=?3/2 or 5/2). It has recently been shown that the state responsible for the multiline signal is converted to that responsible for the g?=?4.1 signal upon the absorption of near-infrared light [Boussac A, Girerd J-J, Rutherford AW (1996) Biochemistry 35?:?6984–6989]. It is shown here that the yield of the spin interconversion may be variable and depends on the photosystem II (PSII) preparations. The EPR multiline signal detected after near-infrared illumination, and which originates from PSII centers not susceptible to the near-infrared light, is shown to be different from that which originates from infrared-susceptible PSII centers. The total S2-multiline signal results from the superposition of the two multiline signals which originate from these two PSII populations. One S2 population gives rise to a "narrow" multiline signal characterized by strong central lines and weak outer lines. The second population gives rise to a "broad" multiline signal in which the intensity of the outer lines, at low and high field, are proportionally larger than those in the narrow multiline signal. The larger the relative amplitude of the outer lines at low and high field, the higher is the proportion of the near-infrared-susceptible PSII centers and the yield of the multiline to g?=?4.1 signal conversion. This inhomogeneity of the EPR multiline signal is briefly discussed in terms of the structural properties of the Mn4 complex.  相似文献   

5.
An abnormal, structurally modified, kinetically stable S2-state has been reported to be induced when Photosystem II was treated with NaCl-EGTA (or EDTA) in the light or with pH in darkness, both are assumed to release functional Ca2+. In order to compare the mechanism of induction of modified S2-state between the two treatments, effects of illumination during or before low pH-treatment on formation of the abnormal S2-state were investigated by means of thermoluminescence measurements and low temperature EPR spectroscopy. Following results have been obtained: Flash illumination during low pH-treatment did not practically induce the abnormal S2-state, whereas preflash illumination given immediately before low pH-treatment efficiently induced the abnormal S2-state, and its amplitude showed a period-four oscillation on varying the preflash number with maxima at the second and sixth flashes. The abnormal S2-state thus induced by preflashes was identical with the modified S2-state that could be induced in dark-low pH-treated Photosystem II by excitation at 0°C after neutralization to pH 6.5. It was inferred that in low pH-treatment, modified S2-state can be formed from both S2- and S3-states, but its yield from the latter is much higher than from the former, consistent with the early results by Boussac et al. obtained for NaCl-EGTA-light or NaCl-citrate-light treatment.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EDTA ethylenediaminetetraactate - EGTA ethylene glycol bis(-aminoethylether)-N,N,N,N-tetraacetic acid - Mes 2-(N-morpholino)ethanesulfonic acid - PS II Photosystem II  相似文献   

6.
《BBA》1987,891(2):129-137
A chlorophyll-protein complex, capable of photochemical water oxidation and consisting of only one extrinsic protein of 33 kDa in addition to six intrinsic proteins of the Photosystem II reaction center, has been isolated from spinach thylakoids by digitonin extraction, performed at pH 6.0, followed by chromatographic separations using DEAE-Toyopearl 650S as described briefly (Tang, X.S. and Satoh, K. (1985) FEBS Lett. 179, 60–64). The protein complex contained approx. 3–4 manganese atoms, 2 mol plastoquinone-9 and 2 mol low-potential forms of cytochrome b-559 heme per mol of the photoactive primary acceptor, QA. The oxygen evolution of the complex was highly stimulated by the presence of CaCl2 and stabilized by glycerol; the typical rate of 400–500 μmol O2 per mg Chl per h was attained with 2,5-dichlorobenzoquinone and potassium ferricyanide as electron acceptors in the presence of 50 mM CaCl2. The protein complex exhibited a dark-stable EPR Signal II; the microwave power saturation profile of the signal was almost identical with that of oxygen-evolving membrane preparations. The multiline EPR signal ascribable to Kok's S2-state was elicited in this protein complex by illumination at 200 K, as in membrane preparations. These results indicate that the basic machinery of photosynthetic water oxidation is preserved in an almost intact state in the isolated chlorophyll-protein complex.  相似文献   

7.
《BBA》1986,851(2):193-201
The role of chloride on the S-state transition in spinach Photosystem II (PS II) particles was investigated by EPR spectroscopy at low temperature and the following results were obtained. (1) After excitation by continuous light at 200 K, chloride-depleted particles did not show the EPR multiline signal associated with the S2 state, but only showed the broad signal at g = 4.1. The S2 multiline signal was completely restored upon chloride repletion. (2) In the absence of chloride the S2 multiline signal was not induced by a single flash excitation at 0°C. However, upon addition of chloride after the flash the signal was developed in darkness. (3) The amplitude of the multiline S2 signal thus developed upon chloride addition after flash illumination did not show oscillations dependent upon flash number. These results indicate that the O2-evolving complex in chloride-depleted PS II membranes is able to store at least one oxidizing equivalent, a modified S2 state, which does not give rise to the multiline signal. Addition of chloride converts this oxidizing equivalent to the normal S2 state which gives rise to the multiline signal. The modified S2 state is more stable than the normal S2 state, showing decay kinetics about 20-times slower than those of the normal S2 state, and the formation of higher S states is blocked.  相似文献   

8.
Brief saturating light flashes were used to probe the mechanism of inactivation of O2 evolution by Tris in chloroplasts. Maximum inactivation with a single flash and an oscillation with period of four on subsequent flashes was observed. Analyses of the oscillations suggested that only the charge-collecting O2-evolving catalyst of photosystem II (S2-state) was a target of inactivation by Tris. This conclusion was supported by the following observations: (a) hydroxylamine preequilibration caused a three-flash delay in the inactivation pattern; (b) the lifetimes of the Tris-inactivable and S2-states were similar; and (c) reagents accelerating S2 deactivation decreased the lifetime of the inactivable state. Inactivation proved to be moderated by F, the precursor of Signal IIs, as shown by a one flash delay with chloroplasts having high abundance of F. Evidence was obtained for cooperativity effects in inactivation and NH3 was shown to be a competitive inhibitor of the Tris-induced inactivation. S2-dependent inactivation was inhibited by glutaraldehyde fixation of chloroplasts, possibly suggesting that inactivation proceeds via conformational changes of the S2-state.  相似文献   

9.
《BBA》1985,810(2):225-234
The functional interaction between the photosynthetic water-oxidizing enzyme system and the substrate analogues hydroxylamine and hydrazine has been analyzed in isolated class II chloroplasts by measuring the effect of these species on the characteristic oscillation pattern of oxygen yield induced by a flash train. The following was found. (1) At concentrations where both substances cause the pronounced two-flash phase shift (Bouges, B. (1971) Biochim. Biophys. Acta 234, 103–112) the dark equilibration is rather slow with half-times of approx. 1 min. (2) The numerical evaluation of the oscillation patterns reveals quantitative differences between hydroxylamine and hydrazine. The interaction with hydroxylamine is complex. It involves one- and two-electron processes as well as fast reaction steps during the flash sequence. The fast reactions take place only with redox states S2 and S3 of the water-oxidizing enzyme. Furthermore, the redox turnover in the presence of hydroxylamine leads to an S1-state that differs markedly in its susceptibility to hydroxylamine from that of S1 in control chloroplasts. (3) Below a threshold concentration which varies for different preparations the hydrazine effect can be quantitatively described by the assumption that after dark equilibration the agent becomes consumed irreversibly via a reaction with two oxidizing redox equivalents produced by PS II. This process is accomplished during the first two flashes. No further interaction occurs during the flash sequence, so that besides the two-flash phase shift the water-oxidizing enzyme system reveals the normal oxygen-evolution pattern. (4) Based on the analysis of the concentration dependence hydrazine is inferred to interact with the catalytic center of the water-oxidizing enzyme system via a cooperative mechanism including two binding sites. The data are discussed in terms of the kinetics of the dark interaction and its possible rate limitation. Mechanistic aspects (ligand-ligand exchange at the functional manganese cluster and transport step) are considered. Furthermore, possible mechanisms for the redox reaction of hydrazine at the catalytic site are briefly discussed.  相似文献   

10.
A method is described for the isolation and purification of active oxygen-evolving photosystem II (PS II) membranes from the green alga Chlamydomonas reinhardtii. The isolation procedure is a modification of methods evolved for spinach (Berthold et al. 1981). The purity and integrity of the PS II preparations have been assesssed on the bases of the polypeptide pattern in SDS-PAGE, the rate of oxygen evolution, the EPR multiline signal of the S2 state, the room temperature chlorophyll a fluorescence yield, the 77 K emission spectra, and the P700 EPR signal at 300 K. These data show that the PS II characteristics are increased by a factor of two in PS II preparations as compared to thylakoid samples, and the PS I concentration is reduced by approximately a factor ten compared to that in thylakoids.Abbreviations BSA bovine serum albumin - Chl chlorophyll - DCBQ 2,6-dichloro-p-benzoquinone - DCMU (diuron) 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DMQ 2,5-dimethyl-p-benzoquinone - EDTA ethylenediamine tetraacetic acid - EPR electron paramagnetic resonance - Hepes N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - MES 2-[N-Morpholino]ethanesulfonic acid - OEE oxygen evolving enhancer - PS II photosystem II - SDS-PAGE sodium dedocyl sulfate polyacrylamide gel electrophoresis  相似文献   

11.
W F Beck  G W Brudvig 《Biochemistry》1987,26(25):8285-8295
The reaction of hydroxylamine with the O2-evolving center of photosystem II (PSII) in the S1 state delays the advance of the H2O-oxidation cycle by two charge separations. In this paper, we compare and contrast the reactions of hydroxylamine and N-methyl-substituted analogues with the electron-donor side of PSII in both O2-evolving and inactivated [tris(hydroxymethyl)aminomethane- (Tris-) washed] spinach PSII membrane preparations. We have employed low-temperature electron paramagnetic resonance (EPR) spectroscopy in order to follow the oxidation state of the Mn complex in the O2-evolving center and to detect radical oxidation products of hydroxylamine. When the reaction of hydroxylamine with the S1 state in O2-evolving membranes is allowed to proceed to completion, the S2-state multiline EPR signal is suppressed until after three charge separations have occurred. Chemical removal of hydroxylamine from treated PSII membrane samples prior to illumination fails to reverse the effects of the dark reaction, which argues against an equilibrium coordination of hydroxylamine to a site in the O2-evolving center. Instead, the results indicate that the Mn complex is reduced by two electrons by hydroxylamine, forming the S-1 state. An additional two-electron reduction of the Mn complex to a labile "S-3" state probably occurs by a similar mechanism, accounting for the release of Mn(II) ions upon prolonged dark incubation of O2-evolving membranes with high concentrations of hydroxylamine. In N,N-dimethylhydroxylamine-treated, Tris-washed PSII membranes, which lack O2 evolution activity owing to loss of the Mn complex, a large yield of dimethyl nitroxide radical is produced immediately upon illumination at temperatures above 0 degrees C. The dimethyl nitroxide radical is not observed upon illumination under similar conditions in O2-evolving PSII membranes, suggesting that one-electron photooxidations of hydroxylamine do not occur in centers that retain a functional Mn complex. We suggest that the flash-induced N2 evolution observed in hydroxylamine-treated spinach thylakoid membrane preparations arises from recombination of hydroxylamine radicals formed in inactivated O2-evolving centers.  相似文献   

12.
EPR spectroscopy is very useful in studies of the oxygen evolving cycle in Photosystem II and EPR signals from the CaMn4 cluster are known in all S states except S4. Many signals are insufficiently understood and the S0, S1, and S3 states have not yet been quantifiable through their EPR signals. Recently, split EPR signals, induced by illumination at liquid helium temperatures, have been reported in the S0, S1, and S3 states. These split signals provide new spectral probes to the S state chemistry. We have studied the flash power dependence of the S state turnover in Photosystem II membranes by monitoring the split S0, split S1, split S3 and S2 state multiline EPR signals. We demonstrate that quantification of the S1, S3 and S0 states, using the split EPR signals, is indeed possible in samples with mixed S state composition. The amplitudes of all three split EPR signals are linearly correlated to the concentration of the respective S state. We also show that the S1 → S2 transition proceeds without misses following a saturating flash at 1 °C, whilst substantial misses occur in the S2 → S3 transition following the second flash.  相似文献   

13.
The YZ decay kinetics in a formal S−1 state, regarded as a reduced state of the oxygen evolving complex, was determined using time-resolved EPR spectroscopy. This S−1 state was generated by biochemical treatment of thylakoid membranes with hydrazine. The steady-state oxygen evolution of the sample was used to optimize the biochemical procedure for performing EPR experiments. A high yield of the S−1 state was generated as judged by the two-flash delay in the first maximum of oxygen evolution in Joliot flash-type experiments. We have shown that the YZ re-reduction rate by the S−1 state is much slower than that of any other S-state transition in hydrazine-treated samples. This slow reduction rate in the S−1 to S0 transition, which is in the order of the S3 to S0 transition rate, suggests that this transition is accompanied by some structural rearrangements. Possible explanations of this unique, slow reduction rate in the S−1 to S0 transition are considered, in light of earlier observations by others on hydrazine/hydroxylamine reduced PS II samples.  相似文献   

14.
《BBA》1987,890(1):6-14
The removal of peripheral membrane proteins of a molecular mass of 17 and 23 kDa by washing of spinach Photosystem-II (PS II) membranes in 1 M salt between pH 4.5 and 6.5 produces a minimal loss of the S1 → S2 reaction, as seen by the multiline EPR signal for the S2 state of the water-oxidizing complex, while reversibly inhibiting O2 evolution. The multiline EPR signal simplifies from a ‘19-line’ spectrum to a ‘16-line’ spectrum, suggestive of partial uncoupling of a cluster of 3 or 4 to yield photo-oxidation of a binuclear Mn site. Alkaline salt washing progressively releases a 33 kDa peripheral protein between pH 6.5 and 9.5, in direct parallel with the loss of O2 evolution and the S2 multiline EPR signal. The 33 kDa protein can be partially removed (20%) at pH 8.0 prior to managanese release. Salt treatment releases four Mn ions between pH 8.0 and 9.5 with the first 2 or 3 Mn ions released cooperatively. A common binding site is thus suggested in agreement with earlier EPR spectroscopic data establishing a tetranuclear Mn site. At least two of these Mn ions bind directly at a site in the PS II complex for which photooxidation by the reaction center is controlled by the 33 kDa protein. The washing of PS II membranes with 1 M CaCl2 to affect the release of the 33 kDa protein, while preserving Mn binding to the membrane (Ono, T.-A. and Inoue, Y. (1983) FEBS Lett. 164, 255–260), is found to leave some 33 kDa protein undissociated in proportion to the extent of O2 evolution and S2 multiline yield. These depleted membranes do not oxidize water or produce the normal S2 state without the binding of the 33 kDa protein. A method for the accurate determination of relative concentrations of the peripheral membrane proteins using gel electrophoresis is presented.  相似文献   

15.
The long-lived, light-induced radical YD of the Tyr161 residue in the D2 protein of Photosystem II (PSII) is known to magnetically interact with the CaMn4 cluster, situated ∼ 30 Å away. In this study we report a transient step-change increase in YD EPR intensity upon the application of a single laser flash to S1 state-synchronised PSII-enriched membranes from spinach. This transient effect was observed at room temperature and high applied microwave power (100 mW) in samples containing PpBQ, as well as those containing DCMU. The subsequent decay lifetimes were found to differ depending on the additive used. We propose that this flash-induced signal increase was caused by enhanced spin relaxation of YD by the OEC in the S2 state, as a consequence of the single laser flash turnover. The post-flash decay reflected S2 → S1 back-turnover, as confirmed by their correlations with independent measurements of S2 multiline EPR signal and flash-induced variable fluorescence decay kinetics under corresponding experimental conditions. This flash-induced effect opens up the possibility to study the kinetic behaviour of S-state transitions at room temperature using YD as a probe.  相似文献   

16.
We have investigated the effects of temperature on the formation and decay of the light-induced multiline EPR signal species associated with photosynthetic oxygen evolution (Dismukes, G.C. and Siderer, Y. (1980) FEBS Lett. 121, 78–80). (1) The decay rate following illumination is temperature dependent: at 295 K the half-time of decay is about 40 s, at 253 K the half-time is approx. 40 min. (2) A single intense flash of light becomes progressively less effective in generating the multiline signal below about 240 K. (3) Continuous illumination is capable of generating the signal down to almost 160 K. (4) Continuous illumination after a preilluminating flash generates less signal above 200 K than at lower temperatures. Our results support the conclusion of Dismukes and Siderer that the S2 state gives rise to this multiline signal; we find that the S1 state can be fully advanced to the S2 state at temperatures as low as 160 K. The S2 state is capable of further advancement at temperatures above about 210 K, but not below that temperature.  相似文献   

17.
W F Beck  G W Brudvig 《Biochemistry》1986,25(21):6479-6486
The binding of several primary amines to the O2-evolving center (OEC) of photosystem II (PSII) has been studied by using low-temperature electron paramagnetic resonance (EPR) spectroscopy of the S2 state. Spinach PSII membranes treated with NH4Cl at pH 7.5 produce a novel S2-state multiline EPR spectrum with a 67.5-G hyperfine line spacing when the S2 state is produced by illumination at 0 degrees C [Beck, W. F., de Paula, J. C., & Brudvig, G. W. (1986) J. Am. Chem. Soc. 108, 4018-4022]. The altered hyperfine line spacing and temperature dependence of the S2-state multiline EPR signal observed in the presence of NH4Cl are direct spectroscopic evidence for coordination of one or more NH3 molecules to the Mn site in the OEC. In contrast, the hyperfine line pattern and temperature dependence of the S2-state multiline EPR spectrum in the presence of tris(hydroxymethyl)aminomethane, 2-amino-2-ethyl-1,3-propanediol, or CH3NH2 at pH 7.5 were the same as those observed in untreated PSII membranes. We conclude that amines other than NH3 do not readily bind to the Mn site in the S2 state because of steric factors. Further, NH3 binds to an additional site on the OEC, not necessarily located on Mn, and alters the stability of the S2-state g = 4.1 EPR signal species. The effects on the intensities of the g = 4.1 and multiline EPR signals as the NH3 concentration was varied indicate that both EPR signals arise from the same paramagnetic site and that binding of NH3 to the OEC affects an equilibrium between two configurations exhibiting the different EPR signals.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

18.
《BBA》1987,890(1):32-38
In PS-II-enriched membranes lacking the three extrinsic water-soluble proteins in the oxygen-evolving system (18, 24 and 33 kDa), but still evolving oxygen to some extent, the formation of the multiline EPR signal originating from the S2-state is dependent on the concentration of Cl. In 200 mM Cl the multiline signal was observed after the first flash and oscillated with the flash number with a period of four. At 20 mM Cl no signal could be observed in this material. These results suggest that the extrinsic proteins are not necessary for multiline signal formation and that complete advancement through the S-states can occur in their absence when sufficient Cl is present.  相似文献   

19.
Flash-induced amperometric signals were measured with a Joliot-type O2 rate electrode in spinach Photosystem II (PS II) membrane fragments exposed to very low concentrations of added hydroxylamine or hydrogen peroxide. In both cases anomalous O2 signals were observed on the first two flashes, and oscillating four-flash patterns were observed on subsequent flashes. The anomalous signals were eliminated in the presence of catalase but not EDTA. The rise times of the O2-release kinetics associated with the anomalous signals were slow (ca. 20 ms with NH2OH and ca. 120 ms with H2O2) compared to the kinetics of O2 release on subsequent flashes and in control membranes (3–6 ms). It is proposed that when the intact PS II O2-evolving complex is perturbed with small concentrations of added reductant, H2O2 can gain access and bind to the complex. Bound H2O2 can then reduce lower S states in some centers leading to anomalous O2 signals on the first two flashes. A model is presented to explain both types of anomalous O2 production. Oxygen observed on the third and subsequent flashes is due to the normal photosynthetic O2-evolution process arising from the S3-state. Anomalous O2 production could be a protective mechanism in PS II centers subjected to stress conditions.Abbreviations DCIP 2,6-dichlorophenolindophenol - EDTA ethylenediaminetetraacetic acid - MES 4-morpholine-ethanesulfonic acid - OEC oxygen-evolving complex - PS II Photosystem II - Yi O2 flash yield on the ith flash - Yss steady-state O2 flash yield level in algae, chloroplasts, or thylakoids after flash-driven S-state oscillations have been damped Formerly, the Solar Energy Research Institute and operated by the Midwest Research Institute for the US Department of Energy under Contract DE-AC-02-83CH10093. Government and MRI retain non-exclusive, royalty-free license to publish or reproduce published articles, or allow others to do so for Government purposes.  相似文献   

20.
A comparative study of X-band EPR and ENDOR of the S2 state of photosystem II membrane fragments and core complexes in the frozen state is presented. The S2 state was generated either by continuous illumination at T=200 K or by a single turn-over light flash at T=273 K yielding entirely the same S2 state EPR signals at 10 K. In membrane fragments and core complex preparations both the multiline and the g=4.1 signals were detected with comparable relative intensity. The absence of the 17 and 23 kDa proteins in the core complex preparation has no effect on the appearance of the EPR signals. 1H-ENDOR experiments performed at two different field positions of the S2 state multiline signal of core complexes permitted the resolution of four hyperfine (hf) splittings. The hf coupling constants obtained are 4.0, 2.3, 1.1 and 0.6 MHz, in good agreement with results that were previously reported (Tang et al. (1993) J Am Chem Soc 115: 2382–2389). The intensities of all four line pairs belonging to these hf couplings are diminished in D2O. A novel model is presented and on the basis of the two largest hfc's distances between the manganese ions and the exchangeable protons are deduced. The interpretation of the ENDOR data indicates that these hf couplings might arise from water which is directly ligated to the manganese of the water oxidizing complex in redox state S2.Abbreviations cw continuous wave - ENDOR electron nuclear double resonance - EPR electron paramagnetic resonance - hf hyperfine - hfc hyperfine coupling - MLS multiline signal - PS II Photosystem II - rf radio frequency - WOC water oxidizing complex  相似文献   

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