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1.
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 (HA Z) 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 p K 1 = 5.8 and p K 2 = 8.0. The pH dependence of the O 2-evolution mediated by PS II membranes is also bellshaped (p K 2 = 7.6). The pH dependence of the process of electron donation from exogenous donors in PS II(–Mn) was studied to determine the location of the alkaline pH sensitive site of the electron transport chain. The data of the study showed that the decrease in the iron cation binding efficiency at pH > 7.0 during blocking was determined by the donor side of the PS II(–Mn). Mössbauer spectroscopy revealed that incubation of PS II(–Mn) membranes in a buffer solution containing 57Fe(II) + 57Fe(III) was accompanied by binding only Fe(III) cations. The pH dependence of the nonspecific Fe(III) cation binding is also described by the same bell-shaped curve with p K 2 = 8.1. The treatment of the PS II(–Mn) membranes with the histidine modifier diethylpyrocarbonate resulted in an increase in the iron binding strength at alkaline pH. It is suggested that blocking efficiency at alkaline pH is determined by competition between OH – and histidine ligand for Fe(III). Because the high-affinity Mn-binding site contains no histidine residue, this fact can be regarded as evidence that histidine is located at another (other than high-affinity) Fe(III) binding site. In other words, this means that the blockage of the high-affinity Mn-binding site is determined by at least two iron cations. We assume that inactivation of oxygen-evolving complex and inhibition of photoactivation in the alkaline pH region are also determined by competition between OH – and a histidine residue involved in coordination of manganese cation outside the high-affinity site. 相似文献
2.
The role of carboxylic residues at the high-affinity, Mn-binding site in the ligation of iron cations blocking the site [Biochemistry 41 (2000) 5854] was studied, using a method developed to extract the iron cations blocking the site. We found that specifically bound Fe(III) cations can be extracted with citrate buffer at pH 3.0. Furthermore, citrate can also prevent the photooxidation of Fe(II) cations by Y Z. Participation of a COOH group(s) in the ligation of Fe(III) at the high-affinity site was investigated using 1-ethyl-3-[(3-dimethylamino)propyl] carbodiimide (EDC), a chemical modifier of carboxylic amino acid residues. Modification of the COOH groups inhibits the light-induced oxidation of exogenous Mn(II) cations by Mn-depleted photosystem II (PSII[−Mn]) membranes. The rate of Mn(II) oxidation saturates at ≥10 μM in PSII(−Mn) membranes and ≥500 μM in EDC-treated PSII (−Mn) samples. Intact PSII(−Mn) membranes have only one site for Mn(II) oxidation via Y Z (dissociation constant, Kd = 0.64 μM), while EDC-treated PSII(−Mn) samples have two sites ( Kd = 1.52 and 22 μM; the latter is the low-affinity site). When PSII(−Mn) membranes were incubated with Fe(II) before modifier treatment (to block the high-affinity site) and the blocking iron cations were extracted with citrate (pH 3.0) after modification, the membranes contained only one site ( Kd = 2.3 μM) for exogenous Mn(II) oxidation by Y Z radical. In this case, the rate of electron donation via Y Z saturated at a Mn(II) concentration ≥15 μM. These results indicate that the carboxylic residue participating in Mn(II) coordination and the binding of oxidized manganese cations at the HA Z site is protected from the action of the modifier by the iron cations blocking the HA Z site. We concluded that the carboxylic residue (D1 Asp-170) participating in the coordination of the manganese cation at the HA Z site (Mn4 in the tetranuclear manganese cluster [Science 303 (2004) 1831]) is also involved in the ligation of the Fe cation(s) blocking the high-affinity Mn-binding site. 相似文献
3.
After a complete removal of Mn from pea subchloroplast photosystem-II (PS II) preparations the electron phototransfer and oxygen evolution are restored upon addition of Mn 2+ and Ca 2+. Pre-illumination of the sample in the absence of Mn 2+ leads to photoinhibition (PI) — irreversible loss of the capability of PS II to be reactivated by Mn 2+. The effect of PI is considerably decreased in the presence of Mn 2+ (4 Mn atoms per reaction center of PS II) and it is increased in the presence of ferricyanide or p-benzoquinone revealing the oxidative nature of the photoeffect. PI results in suppression of oxygen evolution, variable fluorescence, photoreduction of 2,6-dichlorophenol indophenol from either water or diphenylcarbazide. However, photooxidation of chlorophyll P 680, the primary electron donor of PS II as well as dark and photoinduced EPR signal II (ascribed to secondary electron donors D
1 and Z) are preserved. PI is accompanied by photooxidation of 2–3 carotenoid molecules per PS II reaction center (RC) that is accelerated in the presence of ferricyanide and is inhibited upon addition of Mn 2+ or diuron. The conclusion is made that PI in the absence of Mn leads to irreversible oxidative inactivation of electron transfer from water to RC of PS II which remains photochemically active. A loss of functional interaction of RC with the electron transport chain as a common feature for different types of PS II photoinhibition is discussed.Abbreviations A
photoinduced absorbance changes
- DPC
diphenylcarbazide
- DPIP
2,6-dichlorophenol indophenol
-
F
o
constant fluorescence of chlorophyll
- F
photoinduced changes of Chl fluorescence yield
- Mn
manganese
- P 680
the primary electron donor in PS II
- PI
photoinhibition
- PS II
photosystem II
-
Q
the primary (quinone) electron acceptor in PS II
- RC
reaction center 相似文献
4.
Ferrous iron cations Fe(II) can effectively bind to the donor side of the manganese-depleted photosystem II (PSII(-Mn)) and in this way block electron transfer from diphenylcarbazide (DPC) to the major donor for P680, Y Z. The present study was focused on the characteristic features of this process. The oxidation and subsequent binding of Fe(II) cations to PSII(-Mn) may proceed in the absence of an artificial electron acceptor, and therefore we investigated the role of O 2 as a putative endogenous acceptor. Oxygen was shown to participate in the blockade of Y Z by Fe cations, apparently as a structural element of Fe cluster formed at the donor side of PSII(-Mn). The kinetic study of blocking Y Z by Fe(II) as dependent on light intensity demonstrated that the quantum efficiency of Fe cations binding to the donor side of PSII(-Mn) considerably exceeded that of Mn cations. We also compared the possibilities of extracting the native Mn cluster and reconstructed Fe cations from PSII and an alternative electron transport from DPC to P680 + under the conditions of the Y Z blockade by Fe cations. Neither an alternative donor for P680, Y D , nor cytochrome b
559 participated in the latter process. As a whole, our evidence shows that many features of binding Fe cation to the donor side of PSII(-Mn) are in common with photoassembling the Mn cluster.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 12–20.Original Russian Text Copyright © 2005 by Lovyagina, Davletshina, Kultysheva, Timofeev, Ivanov, Semin. 相似文献
5.
The diphenylcarbazide(DPC)/Mn2+ assay [Hsu, B.-D., Lee, J.-Y., & Pan, R.-L. (1987) Biochim. Biophys. Acta 890, 89-96] was used to assess the amount of the high-affinity Mn-binding site in manganese-depleted photosystem II (PS II) membrane fragments from spinach and Scenedesmus obliquus. The assay mechanism at high DPC concentration was shown to involve noncompetitive inhibition of only half of the control level of DPC donation to PS II by micromolar concentrations of Mn at pH 6.5 (i.e., one of two DPC donation sites is inhibited). At low DPC concentration both DPC and Mn2+ donate to PS II additively. Treatment with the carboxyl amino acid modifier 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) inhibited half of the high-affinity Mn-binding site in spinach and Scenedesmus WT PS II membranes and all of the available site in Scenedesmus LF-1 mutant PS II membranes. A similar EDC concentration dependence was observed in all cases. Addition of 2 mM MnCl2 to the 10 mM EDC modification buffer provided complete protection for the Mn-binding site from modification. This protection was specific for Mn2+; six other divalent cations were ineffective. We conclude that EDC modifies that half of the high-affinity Mn-binding site that is insensitive to the histidine modifier diethyl pyrocarbonate (DEPC) [Seibert, M., Tamura, N., & Inoue, Y. (1989) Biochim. Biophys. Acta 974, 185-191] and directly affects ligands that bind Mn. The effects of EDC and DEPC that influence the high-affinity site are mutually exclusive and are specific to the lumenal side of the PS II membrane. Removal of the two more loosely bound of the four functional Mn from PS II membranes uncovers that part of the high-affinity site associated with carboxyl but not histidyl residues. We suggest that carboxyl residues on reaction center proteins are associated with half of the high-affinity Mn-binding site in PS II and are involved along with histidine residues in binding Mn functional in the O2-evolving process. 相似文献
6.
The role of carboxylic residues at the high-affinity, Mn-binding site in the ligation of iron cations blocking the site [Biochemistry 41 (2000) 5854] was studied, using a method developed to extract the iron cations blocking the site. We found that specifically bound Fe(III) cations can be extracted with citrate buffer at pH 3.0. Furthermore, citrate can also prevent the photooxidation of Fe(II) cations by YZ. Participation of a COOH group(s) in the ligation of Fe(III) at the high-affinity site was investigated using 1-ethyl-3-[(3-dimethylamino)propyl] carbodiimide (EDC), a chemical modifier of carboxylic amino acid residues. Modification of the COOH groups inhibits the light-induced oxidation of exogenous Mn(II) cations by Mn-depleted photosystem II (PSII[-Mn]) membranes. The rate of Mn(II) oxidation saturates at > or = 10 microM in PSII(-Mn) membranes and > or = 500 microM in EDC-treated PSII (-Mn) samples. Intact PSII(-Mn) membranes have only one site for Mn(II) oxidation via YZ (dissociation constant, Kd = 0.64 microM), while EDC-treated PSII(-Mn) samples have two sites (Kd = 1.52 and 22 microM; the latter is the low-affinity site). When PSII(-Mn) membranes were incubated with Fe(II) before modifier treatment (to block the high-affinity site) and the blocking iron cations were extracted with citrate (pH 3.0) after modification, the membranes contained only one site (Kd = 2.3 microM) for exogenous Mn(II) oxidation by Y(Z)() radical. In this case, the rate of electron donation via YZ saturated at a Mn(II) concentration > or = 15 microM. These results indicate that the carboxylic residue participating in Mn(II) coordination and the binding of oxidized manganese cations at the HAZ site is protected from the action of the modifier by the iron cations blocking the HAZ site. We concluded that the carboxylic residue (D1 Asp-170) participating in the coordination of the manganese cation at the HAZ site (Mn4 in the tetranuclear manganese cluster [Science 303 (2004) 1831]) is also involved in the ligation of the Fe cation(s) blocking the high-affinity Mn-binding site. 相似文献
7.
Formation of thermoluminescence signals is characteristics of energy- and charge storage in Photosystem II. In isolated D1/D2/cytochrome b-559 Photosystem II reaction centre preparation four thermoluminescence components were found. These appear at -180 (Z band), between -80 and -50 (Z v band), at -30 and at +35°C. The Z band arises from pigment molecules but not correlated with photosynthetic activity. The Z v and -30°C bands arise from the recombination of charge pairs stabilized in the Photosystem II reaction centre complex. The +35°C band probably corresponds to the artefact glow peak resulting from a pigment-protein-detergent interaction in subchloroplast preparations (Rózsa Zs, Droppa M and Horváth G (1989) Biochim Biophys Acta 973, 350–353).Abbreviations Chl
chlorophyll
- Cyt
cytochrome
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- D1
psbA gene product
- D2
psbD gene product
- P680
primary electron donor of PS II
- Pheo
pheophytin
- PS II
Photosystem II
- Q A
primary quinone acceptor of PS II
- Q B
secondary quinone acceptor of PS II
- RC
reaction centre of PS II
- TL
thermoluminescence 相似文献
8.
It is shown that restoration of photoinduced electron flow with added Mn 2+ (measured by photoreduction of DCPIP and photoinduced change of chlorophyll fluorescence yield) in Mn-depleted Photosystem II (PS II) membrane fragments isolated from spinach chloroplasts, is considerably increased by exogenous histidine (His). The stimulating effect of His is not observed if other electron donors (NH 2OH or diphenylcarbazide) are used instead of Mn 2+. His added alone does not induce electron transfer in Mn-depleted PS II preparations. Investigation of pH dependence of the stimulating effect of 2 mM His shows that the effect is observed only at pH > 5.0, it gives a 50% activation around pH 6.0 and saturates at pH 7.0–7.5. Nearly 200 μM His is required for a 50 effect at pH 7.0. It is suggested that the added His can be involved in stimulation of electron transfer on the donor side of PS II through direct interaction of Mn 2+ with deprotonated form(s) of His resulting in formation of Mn–His complexes capable of efficient electron donation to PS II (though it is not excluded that His serves as a base that takes part in proton exchange coupled with redox reactions on the donor side of PS II or as an electron donor to the oxidized Mn). 相似文献
9.
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. in Journal of Bioenergetics and Biomembranes 48:227, 2016; Semin et al. in Journal of Photochemistry and Photobiology B 178:192, 2018). In the current study, we examined the effect of Ca2+ cations on the interaction of Fe(II) ions with Mn-depleted [PSII(-Mn)] and Ca-depleted [PSII(-Ca)] photosystem II membranes. We found that Ca2+ cations (about 50 mM) inhibit the light-dependent oxidation of Fe(II) (5 µM) by about 25% in PSII(-Mn) membranes, whereas inhibition of the blocking process is greater at about 40%. Blocking of the HA site by Fe cations also decreases the rate of charge recombination between QA? and YZ?+ from t1/2?=?30 ms to 46 ms. However, Ca2+ does not affect the rate during the blocking process. An Fe(II) cation (20 µM) replaces 1Mn cation in the Mn4CaO5 catalytic cluster of PSII(-Ca) membranes at pH 5.7 but 2 Mn cations at pH 6.5. In the presence of Ca2+ (10 mM) during the substitution process, Fe(II) is not able to extract Mn at pH 5.7 and extracts only 1Mn at pH 6.5 (instead of two without Ca2+). Measurements of fluorescence induction kinetics support these observations. Inhibition of Mn substitution with Fe(II) cations in the OEC only occurs with Ca2+ and Sr2+ cations, which are also able to restore oxygen evolution in PSII(-Ca) samples. Nonactive cations like La3+, Ni2+, Cd2+, and Mg2+ have no influence on the replacement of Mn with Fe. These results show that the location and/or ligand composition of one Mn cation in the Mn4CaO5 cluster is strongly affected by calcium depletion or rebinding and that bound calcium affects the redox potential of the extractable Mn4 cation in the OEC, making it resistant to reduction. 相似文献
10.
Divalent salt-washing of O 2-evolving PS II particles caused total liberation of 33-, 24- and 16-kDa proteins, but the resulting PS II particles retained almost all amounts of Mn present in initial particles. The retained Mn was EPR-silent when the particles were kept in high concentrations of divalent salt. By divalent salt-washing, the activity of diphenylcarbazide (DPC) photooxidation was not affected at all, neither suppressed nor enhanced, while O 2 evolution was totally inactivated. These results indicate that Mn can be kept associated with PS II particles even after liberation of the 33-kDa protein, and suggest that the 33-kDa protein is probably not responsible for binding Mn onto membranes, but is possibly responsible for maintaining the function of Mn atoms in the O 2-evolving center. 相似文献
11.
The effect of desiccation and rehydration on the function of Photosystem II has been studied in the desiccation tolerant lichen Cladonia convoluta by thermoluminescence. We have shown that in functional fully hydrated thalli thermoluminescence signals can be observed from the recombination of the S 2(3)Q B
– (B band), S 2Q A
– (Q band), Tyr-D +Q A
– (C band) and Tyr-Z +(His +)Q A
– (A band) charge stabilization states. These thermoluminescence signals are completely absent in desiccated thalli, but rapidly reappear on rehydration. Flash-induced oscillation in the amplitude of the thermoluminescence band from the S 2(3)Q B
– recombination shows the usual pattern with maxima after 2 and 6 flashes when rehydration takes place in light. However, after rehydration in complete darkness, there is no thermoluminescence emission after the 1 st flash, and the maxima of the subsequent oscillation are shifted to the 3rd and 7th flashes. It is concluded that desiccation of Cladonia convoluta converts PS II into a nonfunctional state. This state is characterized by the lack of stable charge separation and recombination, as well as by a one-electron reduction of the water-oxidizing complex. Restoration of PS II function during rehydration can proceed both in the light and in darkness. After rehydration in the dark, the first charge separation act is utilized in restoring the usual oxidation state of the water-oxidizing comples.Abbreviations Chl
chlorophyll
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DT
desiccation tolerant
- PS II
Photosystem II
- TL
thermoluminescence
- P 680
reaction center Chl of PS II
- Q A and Q B
puinone electron acceptors of PS II
- S 0,...,S 4
the redox states of the water-oxidizing complex
- Tyr-Z and Tyr-D
redox-active tyrosine electron donors of PS II 相似文献
12.
The donation of electrons by Mn(II) and Fe(II) to Y(Z*) through the high-affinity (HA(Z)) site in Mn-depleted photosystem II (PSII) membranes has been studied by flash-probe fluorescence yield measurements. Mn(II) and Fe(II) donate electrons to Y(Z*) with about the same efficiency, saturating this reaction at the same concentration (ca. 5 microM). However, following a short incubation of the membranes with 5 microM Fe(II), but not with Mn(II) in room light, added Mn(II) or Fe(II) can no longer be photooxidized by Y(Z)(*). This blocking effect is caused by specifically bound, photooxidized Fe [> or =Fe(III)] and is accompanied by a delay in the fluorescence yield decay kinetics attributed to the slowing down of the charge recombination rate between Q(a-) and Y(Z*). Exogenously added Fe(III), on the other hand, does not donate electrons to Y(Z*), does not block the donation of electrons by added Mn(II) and Fe(II), and does not change the kinetics of the decay of the fluorescence yield. These results demonstrate that the light-dependent oxidation of Fe(II) by Y(Z*) creates an Fe species that binds at the HA(Z) site and causes the blocking effect. The pH dependence of Mn(II) electron donation to Y(Z*) via the HA(Z) site and of the Fe-blocking effect is different. These results, together with sequence homologies between the C-terminal ends of the D1 and D2 polypeptides of the PSII reaction center and several diiron-oxo enzymes, suggest the involvement of two or perhaps more (to an upper limit of four to five) bound iron cations per reaction center of PSII in the blocking effect. Similarities in the interaction of Fe(II) and Mn(II) with the HA(Z) Mn site of PSII during the initial steps of the photoactivation process are discussed. The Fe-blocking effect was also used to investigate the relationship between the HA(Z) Mn site and the HA sites on PSII for diphenylcarbazide (DPC) and NH2OH oxidation. Blocking of the HA(Z) site with specifically bound Fe leads to the total inhibition of electron donation to Y(Z*) by DPC. Since DPC and Mn(II) donation to PSII is noncompetitive [Preston, C., and Seibert, M. (1991) Biochemistry 30, 9615-9624], the Fe bound to the HA(Z) site can also block the DPC donation site. On the other hand, electron donation by NH2OH to PSII still occurs in Fe-blocked membranes. Since hydroxylamine does not reduce the Fe [> or =Fe(III)] specifically bound to the HA(Z) site, NH2OH must donate to Y(Z*) through its own site or directly to P680+. 相似文献
13.
The O 2-evolution deficient mutant (LF-1) of Scenedesmus obliquus inserts an unprocessed D1 protein into the thylakoid membrane and binds less than half the wild type (WT) level of Mn. LF-1 photosystem II (PS II) membrane fragments lack that part of the high-affinity Mn 2+-binding site found in WT membranes which may be associated with histidine residues on the D1 protein (Seibert et al. 1989 Biochim Biophys Acta 974: 185–191). Hsu et al. (1987 Biochim Biophys Acta 890: 89–96) purport that the high-affinity site (characterized by competitive inhibition of DPC-supported DCIP photoreduction by M concentrations of Mn 2+) in Mn-extracted PS II membranes is also the binding site for Mn functional in O 2 evolution. Proteases (papain, subtilisin, and carboxypeptidase A) can be used to regenerate the high-affinity Mn 2+-binding site in LF-1 PS II membranes but not in thylakoids. Experiments with the histidine modifier, DEPC, suggest that the regenerated high-affinity Mn 2+-binding sites produced by either subtilisin or carboxypeptidase A treatments were the same sites observed in WT membranes. However, none of the protease treatments produced LF-1 PS II membranes that could be photoactivated. Reassessment of the processing studies of Taylor et al. (1988 FEBS Lett 237: 229–233) lead us to believe that their procedure also does not result in substantial photoactivation of LF-1 PS II membranes. We conclude that (1) the unprocessed carboxyl end of the D1 protein in LF-1 is located on the lumenal side of the PS II membrane, (2) the unprocessed fragment physically obstructs or perturbs that part of the high-affinity Mn 2+-binding site undetectable in LF-1, and (3) the D1 protein must be processed at the time of insertion into the membrane for normal O 2-evolution function to result.Abbreviations Chl
chlorophyll
- DCBQ
2,6-dichloro-1,4-benzoquinone
- DCIP
2,6-dichlorophenol indophenol
- DEPC
diethylpryocarbonate
- DPC
1,5-diphenylcarbazide
- HEPES
4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid
- LDS-PAGE
lithium dodecylsulfate polyacrylamide gel electrophoresis
- LF-1
a low-fluorescent mutant of Scenedesmus obliquus
- MES
4-morpholineethanesulfonic acid
- PS II
photosystem II
- PMSF
phenylmethylsulfonyl fluoride
- RC
photosystem II reaction center
- Tris
tris(hydroxymethyl)aminomethane
- WT
wild type
Operated by the Midwest Research Institute for the U.S. Department of Energy under contract DE-AC-02-83CH10093. 相似文献
14.
Electron donation to Photosystem II (PS II) by diphenylcarbazide (DPC) is interrupted by the presence of endogenous Mn in PS II particles. Removal of this Mn by Tris treatment greatly stimulates the electron transport with DPC as donor. Binding of low concentration of exogenous Mn(II) to Tris-treated PS II particles inhibits DPC photooxidation competitively with DPC. This phenomenon was used to locate a highly specific Mn(II) binding site on the oxidizing side of Photosystem II with dissociation constant about 0.15 μM. The binding of Mn(II) is electrostatic in nature. Its affinity depends not only on the ionic strength, but also on the anion species of the salt in the medium. The effectiveness in decreasing the affinity follows the order F − > SO 2−4 > CH 3COO − > CI − > Br − > NO 3−. This observation is interpreted as follows: smaller ions, like F −, CH 3COO −, and larger ions, like SO 2−4, have inhibitory effects on Mn(II) binding, whereas ions with optimal size, like Cl −, Br − and NO 3−, can stabilize the binding, resembling the anion requirement for reactivation of Cl −-depleted chloroplasts. We suggest that the binding site for Mn(II) we observed is the site for the endogenous Mn in the O 2-evolving complex of PS II. This site remains after Tris treatment, which removes all the endogenous Mn as well as the three extrinsic proteins, indicating that it is on the intrinsic component(s) of PS II reaction centers. Furthermore, the Cl − requirement for O 2 evolution may be attributed, at least partly to its stabilizing effect on Mn binding. 相似文献
15.
The toxicity of heavy metals on photosystem 2 photochemistry, was investigated by monitoring Hill activity, fluorescence, and thermoluminescence properties of photosystem 2 (PS 2) in pea ( Pisum sativum L. cv. Bombay) chloroplasts. In Co 2+-, Ni 2+- or Zn 2+-treated chloroplasts 2,6-dichlorophenolindophenol-Hill activity was markedly inhibited. Addition of hydroxylamine which donates electrons close to PS 2 reaction center did not restore the PS 2 activity. Co 2+-, Ni 2+ or Zn 2+ also inhibited PS 2 activity supported by hydroxylamine in tris (hydroxymethyl)aminomethane (Tris)-inactivated chloroplasts. These observations were confirmed by fluorescence transient measurements. This implies that the metal ions inhibit either the reaction center or the components of PS 2 acceptor side. Flash-induced thermoluminescence studies revealed that the S 2Q ?A charge recombination was insensitive to metal ion addition. The S 2Q ?B charge recombination, however, was inhibited with increase in the level of Co 2+, Ni 2+ or Zn 2+. The observed sensitivity of S 2?B charge recombination in comparison to the stability of S 2Q ?A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. Q B. We suggest that Co 2+, Ni 2+ or Zn 2+ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify Q B site, leading to the loss of PS 2 activity. 相似文献
16.
Photoinhibition was analyzed in O 2-evolving and in Tris-treated PS II membrane fragments by measuring flash-induced absorption changes at 830 nm reflecting the transient P680 + formation and oxygen evolution. Irradiation by visible light affects the PS II electron transfer at two different sites: a) photoinhibition of site I eliminates the capability to perform a stable charge separation between P680 + and Q A
- within the reaction center (RC) and b) photoinhibition of site II blocks the electron transfer from Y Z to P680 +. The quantum yield of site I photoinhibition (2–3×10 -7 inhibited RC/quantum) is independent of the functional integrity of the water oxidizing system. In contrast, the quantum yield of photoinhibition at site II depends strongly on the oxygen evolution capacity. In O 2-evolving samples, the quantum yield of site II photoinhibition is about 10 -7 inhibited RC/quantum. After selective elimination of the O 2-evolving capacity by Tris-treatment, the quantum yield of photoinhibition at site II depends on the light intensity. At low intensity (<3 W/m 2), the quantum yield is 10 -4 inhibited RC/quantum (about 1000 times higher than in oxygen evolving samples). Based on these results it is inferred that the dominating deleterious effect of photoinhibition cannot be ascribed to an unique target site or a single mechanism because it depends on different experimental conditions (e.g., light intensity) and the functional status of the PS II complex.Abbreviations A 830
absorption change at 830 nm
- P680
primary electron donor of PS II
- PS II
photosystem II
- Mes
2(N-morpholino)ethansulfonic acid
- Q A, Q B
primary and secondary acceptors of PS II
- DCIP
2,6-dichlorophenolindophenol
- DPC
1,5-diphenylcarbohydrazide
- FWHM
fullwidth at half maximum
- Ph- p-BQ
phenyl- p-benzoquinone
- PFR
photon fluence rate
- Pheo
pheophytin
- RC
reaction center 相似文献
17.
The functional properties of a purified homogeneous spinach PS II-core complex with high oxygen evolution capacity (Haag et al. 1990a) were investigated in detail by measuring thermoluminescence and oscillation patterns of flash induced oxygen evolution and fluorescence quantum yield changes. The following results were obtained: - Depending on the illumination conditions the PS II-core complexes exhibit several thermoluminescence bands corresponding to the A band, Q band and Zv band in PS II membrane fragments. The lifetime of the Q band (Tmax=10°C) was determined to be 8s at T=10°C. No B band corresponding to S2QB ? or S3QB ? recombination could be detected.
- The flash induced transient fluorescence quantum yield changes exhibit a multiphasi relaxation kinetics shich reflect the reoxidation of Q A ? . In control samples without exogenous acceptors this process is markedly slower than in PS II membrane fragments. The reaction becomes significantly retarded by addition of 10 μM DCMU. After dark incubation in the presence of K3[Fe(CN)6
- Excitation of dark-adapted samples with a train of short saturating flashes gives rise to a typical pattern dominated by a high O2 yield due to the third flash and a highly damped period four oscillation. The decay of redox states S2 and S3 are dominated by short life times of 4.3 s and 1.5 s, respectively, at 20°C.
The results of the present study reveal that in purified homogeneous PS II-core complexes with high oxygen evolution isolated from higher plants by β-dodecylmaltoside solubilization the thermodynamic properties and the kinetic parameters of the redox groups leading to electron transfer from water to Q A are well preserved. The most obvious phenomenon is a severe modification of the Q B binding site. The implications of this finding are discussed. 相似文献
18.
Transport of electrons in spinach photosystem II (PSII) whose oxygen-evolving complex (OEC) contains heterogeneous metal clusters 2Mn2Fe and 3Mn1Fe was studied by measuring the fluorescence induction kinetics (FIK). PSII(2Mn,2Fe) and PSII(3Mn,1Fe) preparations were produced using Cadepleted PSII membranes (PSII(–Ca)). It was found that FIK in PSII(2Mn,2Fe) membranes is similar in form to FIK in PSII(–Ca) samples, but the fluorescence yield is lower in PSII(2Mn,2Fe). The results demonstrate that, just as in PSII(–Ca) preparations, there is electron transfer from the metal cluster in the OEC to the primary plastoquinone electron acceptor QA. They also show that partial substitution of Mn cations with Fe has no effect on the electron transport on the acceptor side of PSII. Thus, these data demonstrate the possibility of water oxidation either by the heterogeneous metal cluster or just by the manganese dimer. We established that FIK in PSII(3Mn,1Fe) preparations are similar in form to FIK in PSII(2Mn,2Fe) membranes but PSII(3Mn,1Fe) is characterized by a slightly higher maximal fluorescence yield, Fmax. The electron transfer rate in PSII(3Mn,1Fe) preparations significantly (by a factor of two) increases in the presence of Ca 2+, whereas Ca 2+ has hardly any effect on the electron transport in PSII(2Mn,2Fe) membranes. In Mndepleted PSII membranes, FIK reaches its maximum (the so-called peak K), after which the fluorescence yield starts to decrease as the result of two factors: the oxidation of reduced primary plastoquinone Q A ? and the absence of electron influx from the donor side of PSII. The replacement of Mn cations by Fe in PSII(?Mn) preparations leads to fluorescence saturation and disappearance of the K peak. This is possibly due to the deceleration of the charge recombination process that takes place between reduced primary electron acceptor Q A ? and oxidized tyrosine Y Z +. which is an electron carrier between the OEC and the primary electron donor P680. 相似文献
19.
Photosystem II membranes were isolated from chloroplasts of pokeweed ( Phytolacca americana) and rendered deficient in Ca 2+, an inorganic cofactor of photosynthetic water oxidation. The thermoluminescence properties of such membranes were found to depend on the Ca 2+-depleting method used. This feature was analyzed with respect to the thermoluminescence emission that accompanied the recombination reaction between the reduced acceptor Q A
– and the oxidant of the S 2 state. It was determined that the differences observed among various preparations of Ca 2+-depleted membranes were attributable to the presence or absence of the extrinsic 23 kDa polypeptide on the membranes. The binding of this polypeptide to Ca 2+-depleted membranes devoid of the 17 and 23 kDa extrinsic polypeptides caused the thermoluminescence to be emitted at a higher temperature due to a further stabilization of an already abnormally stable S 2 state. Addition of the chelators EDTA or EGTA and of citrate brought about a similar response. The conditions required for the upshift of the emission temperature of thermoluminescence strongly resembled those identified by Boussac et al. (FEBS Lett. 277 (1990) 69–74) as responsible for modifying the EPR multiline signal from the S 2 state of Ca 2+-depleted PS II membranes. Consistent with the authors' interpretation of the reason for this modification, we conclude that the elevated emission temperature of the thermoluminescence emission reflects an abnormal ligand environment of the Mn-center in PS II that may be created by a direct ligation of the added agents to Mn. Evidence is also presented that the return to a normal S 2 after an addition of Ca 2+ occurs via yet another condition of S 2 which, in terms of its thermoluminescence properties, resembles that of Ca 2+-depleted membranes before addition of modifying agents, but is not identical to it. 相似文献
20.
The influence of UV-B irradiation on photosynthetic oxygen evolution by isolated spinach thylakoids has been investigated using thermoluminescence measurements. The thermoluminescence bands arising from the S 2Q B
- (B band) and S 2Q A
– (Q band) charge recombination disappeared with increasing UV-B irradiation time. In contrast, the C band at 50°C, arising from the recombination of Q A
- with an accessory donor of Photosystem II, was transiently enhanced by the UV-B irradiation. The efficiency of DCMU to block Q A to Q B electron transfer decreased after irradiation as detected by the incomplete suppression of the B band by DCMU. The flash-induced oscillatory pattern of the B band was modified in the UV-B irradiated samples, indicating a decrease in the number of centers with reduced Q B. Based on the results of this study, UV-B irradiation is suggested to damage both the donor and acceptor sides of Photosystem II. The damage of the water-oxidizing complex does not affect a specific S-state transition. Instead, charge stabilization is enhanced on an accessory donor. The acceptor-side modifications decrease the affinity of DCMU binding. This effect is assumed to reflect a structural change in the Q B/DCMU binding site. The preferential loss of dark stable Q B
- may be related to the same structural change or could be caused by the specific destruction of reduced quinones by the UV-B light.Abbreviations Chl
chlorophyll
- DCMU
3-(3,4,-dichlorophenyl)-1,1-dimethylurea
- PS II
Photosystem II
- Q A
first quinone electron acceptor of PS II
- Q B
second quinone electron acceptor of PS II
- Tyr-D
accessory electron donor of PS II
- S 0-S 4
charge storage states of the water-oxidizing complex 相似文献
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