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1.
The roles of Ca 2+ and Cl − on the photosynthetic O 2 yield under flash illumination have been examined in EDTA-washed preparations of the cyanobacterium Anacystis nidulans. Especially the effect of Cl − deficiency on the O 2 yield and on the S-state distribution was analyzed. As the results show, omission of both Ca 2+ and Cl − (Mn 2+ present) almost totally inhibited O 2 evolution. When Ca 2+ was replaced by Na +, a substantial reduction of the O 2 yield was observed, but only a minor change in the S-state distribution occurred. However, when Cl − was displaced by NO −3, which is equivalent to Cl − deficiency of the water-splitting complex, a substantial reduction of the O 2 yield and in addition a significant change in the S-state distribution was observed. The comparison of deactivation kinetics in NO −3 containing samples with those in control samples indicated that Cl − deficiency allowed accumulation of oxidizing equivalents up to the S 3 state but modified the final step of O 2 evolution. Moreover, those centers which advanced to the S 3 state in the absence of Cl − deactivated in a special way which involved a faster deactivation of S 2 and an increased formation of S −1. 相似文献
2.
1. Rate constants for reduction of paraquat ion (1,1′-dimethyl-4,4′-bipyridy-lium, PQ 2+) to paraquat radical (PQ +·) by e−aq and CO 2−· have been measured by pulse radiolysis. Reduction by e−aq is diffusion controlled ( k = 8.4·10 10 M −1·s −1) and reduction by CO 2−· is also very fast k = 1.5·10 10 M −1·s −1). 2. The reaction of paraquat radical with oxygen has been analysed to give rate constants of 7.7·108 M−1·s−1 and 6.5·108 M−1·s−1 for the reactions of paraquat radical with O2 and O2−·, respectively. The similarity in these rate constants is in marked contrast to the difference in redox potentials of O2 and O2−· (− 0.59 V and + 1.12 V, respectively). 3. These rate constants, together with that for the self-reaction of O2−·, have been used to calculate the steady-state concentration of O2−· under conditions thought to apply at the site of reduction of paraquat in the plant cell. On the basis of these calculations the decay of O2−· appears to be governed almost entirely by its self-reaction, and the concentration 5 μm away from the thylakoid is still 90% of that at the thylakoid itself. Thus, O2−· persists long enough to diffuse as far as the chloroplast envelope and tonoplast, which are the first structures to be damaged by paraquat treatment. O2−· is therefore sufficiently long-lived to be a candidate for the phytotoxic product formed by paraquat in plants. 相似文献
3.
The kinetics of the reaction of hydrated electron (e −aq) and carboxyl anion radical (CO 2) with Pseudomonas aeruginosa ferricytochrome c-551 were studied by pulse radiolysis. The rate of reaction of e −aq with the negatively charged ferricytochrome c-551 (17 nM −1 · s −1) is significantly slower than the larger positively charged horse heart ferricytochrome c (70 nM − · s −). This difference cannot be explained solely by electrostatic effects on the diffusion-controlled reactions. After the initial encounter of e −aq with the protein, ferricytochrome c-551 is less effective in transferring an electron to the heme which may be due to the negative charge on the protein. The charge on ferricytochrome c-551 is estimated to be −5 at pH 7 from the effect of ionic strength on the reaction rate. A slower relaxation (2 · 10 4 s −1) observed after fast e −aq reduction is attributed to a small conformational change. The rate of reaction of CO 2 with ferricytochrome c-551 (0.7 nM −1 · s −) is, after electrostatic correction, the same as ferricytochrome c, indicating that the steric requirements for reaction are similar. This reaction probably takes place through the exposed heme edge. 相似文献
4.
The phospholipid mediator AGEPC (acetyl glyceryl ether phosphorylcholine) was examined for its effects on guinea pig peritoneal macrophages. At a concentration of 10 −9 -10 −6 M, AGEPC evoked release of prostaglandin E (PGE) and thromboxane B 2 (TXB 2) from albumin-elicited macrophages. It also triggerd generation of O −2 by Corynebacterium parvum-induced cells. Moreover, it caused augmented spreading of macrophages. The calmodulin antagonis W-7 attenuated AGEPC-mediated O −2 production and cell spreading whereas prostanoid synthesis was enhanced. These novel actions of AGEPC on the major cellular component of the inflammatory process attest to its role as a potent mediator of immunoinflammatory responses. 相似文献
5.
1. Single reduced methyl viologen (MV .+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ max 600 nm; MV .+, = 1.3 · 10 4 M −1 · cm −1; oxidised form of methyl viologen (MV 2+), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques. 2. A convenient electrochemical preparation of large amounts of MV.+ has been developed. 3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity. 4. The reaction of MV.+ with O2 produced H2O2 (k > 5 · 106 M−1 · s−1, pH 7.5, 25 °C). H2O2 subsequently reacted with excess MV.+ (k = 2.3 · 103 M−1 · s−1, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations. 5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H2O2 (or radicals derived from H2O2) induced damage of plant cell membrane. 相似文献
6.
In whole cells of Rhodospirillum rubrum the light-induced absorbance difference spectrum of the reduction of the first quinone electron acceptor Q 1 was determined in order to relate the emission yield ф and the magnetic field-induced emission increase Δф to the redox state of Q 1. It was found that Δф/ф 2 is a linear function of the number of reaction centers, in which Q 1 is reduced, independent of the fraction of reaction centers in the oxidized state. The emission yield is a hyperbolic function of the fraction of reaction centers closed, either by reduction of the acceptor Q 1 or by oxidation of the primary electron donor P. Apparently, in whole cells of R. rubrum a matrix model for energy transfer between various photosynthetic units can be applied. A model is presented, which is a generalization of theoretical considerations reported before (Duysens, L.N.M. (1978) in Chlorophyll Organization and Energy Transfer in Photosynthesis, Ciba Found. Symp. 61 (New Series), pp. 323–340, Elsevier/North-Holland, Amsterdam) and which is in excellent agreement with the experiments. From simultaneous measurements of Δф and ф the redox state of the reaction center can relatively easily be determined. So far, this is the only method for simultaneously measuring the fractions P + and Q −1 in intact cells under steady-state conditions. 相似文献
7.
O2- generation in mitochondrial electron transport systems, especially the NADPH-coenzyme Q10 oxidoreductase system, was examined using a model system, NADPH-coenzyme Q1-NADPH-dependent cytochrome P-450 reductase. One electron reduction of coenzyme Q1 produces coenzyme Q1-. and O2- during enzyme-catalyzed reduction and O2+ coenzyme Q1-. are in equilibrium with O2- + coenzyme Q1 in the presence of enough O2. The coenzyme Q1-. produced can be completely eliminated by superoxide dismutase, identical to bound coenzyme Q10 radical produced in a succinate/fumarate couple-KCN-submitochondrial system in the presence of O2. Superoxide dismutase promotes electron transfer from reduced enzyme to coenzyme Q1 by the rapid dismutation of O2- generated, thereby preventing the reduction of coenzyme Q1 by O2-. The enzymatic reduction of coenzyme Q1 to coenzyme Q1H2 via coenzyme Q1-. is smoothly achieved under anaerobic conditions. The rate of coenzyme Q1H2 autoxidation is extremely slow, i.e., second-order constant for [O2][coenzyme Q1H2] = 1.5 M-1.s-1 at 258 microM O2, pH 7.5 and 25 degrees C. 相似文献
8.
Estimation of the ammonia production of the shrimp C. crangon in two littoral ecosystems (oligotrophic sand and eutrophic mud) was determined in winter and summer conditions from laboratory observations in experimental microcosms. The ammonia excretion rate of C. crangon was not influenced by either the sediment type or the ammonia concentration of the overlying water; on the other hand, the mean excretion rate and the response to initial handling stress increased markedly as shrimp were deprived of soft substratum. The daily ammonia production of C. crangon was 16 μmol NH3 · g −1 wet wt · day −1 in winter and 40 μmol in summer. A gross production of 12 μmol NH3 · m−2 · day −1 and 300–700 μmol μ m−2 · day−1, respectively, could be expected in the two ecosystems studied. This would account for 5% (winter) and 2–4% (summer) of the total NH+4 flux at the sediment-water interface. The contribution of the excretion of all macrofauna to the NH+4 flux from the sediment is discussed. 相似文献
9.
The kinetics of the displacement reactions of the bromide ligands of trans-[FeBr 2(depe) 2] (depe = Et 2PCH 2CH 2PEt 2) by the organonitrile NCCH 2C 6H 4OMe-4, in tetrahydrofuran (either in the absence or in the presence of added Br −), to give the corresponding mono- and dinitrile complexes trans-[FeBr(NCCH 2C 6H 4OMe-4)(depe) 2] + and trans-[Fe(NCCH 2C 6H 4OMe-4) 2(depe) 2] 2+, have been investigated by stopped-flow spectrophotometry. The substitution reaction occurs by a mechanism involving rate-limiting dissociation of bromo ligands to form the unsaturated intermediates [FeBr(depe) 2] + ( k1 = 1.52 ± 0.02 s −1) and [Fe(NCR)(depe) 2] 2+ ( k3 = 0.063 ± 0.008 s −1) which add the nitrile ligand to form those nitrile complexes. The competition between the nitrile and Br − for such metal centres has also been investigated and a stronger inhibiting effect of added Br − is observed for the substitution of the second bromo ligand relative to the first one. The kinetic data are rationalized in terms of π-electronic effects of these unsaturated metal centres and of the bromide and nitrile ligands. 相似文献
10.
1. Incubated chicken eggs (D14 to D21) were placed separately in transparent acrylic glass chambers which were immersed in a 37.5°C water bath for 3 h. The chambers were then moved for 3 h to another water bath controlled at 34.5°C. Oxygen consumption and temperature of the allantoic fluid ( Taf) were measured at 5-min intervals for the whole experiment using an oxygen analyzer and CrNi–Ni-thermocouples, respectively. Heat production (HP) was calculated, using an assumed RQ of 0.72. 2. At 37.5°C the relationship between HP and embryonic age follows a sigmoid curve. Between D18 (HP 7.25 J g−1 h; 2.01 W kg−1) and D19 (HP 7.21 J g−1 h−1; 2.00 W kg−1) this function had a plateau phase with a duration of about 24 h. 3. During the cooling process, HP decreased continuously and the relationship between Ta and HP could be described by an exponential function. From the results, it was possible to calculate the relationships between Taf, as a measure of body core temperature, and Q10; the lower the Taf the higher the Q10. 4. Because the actual measured HP is the result of the negative effect of Q10 on HP and the stimulating influence of the CNS-generated HP, a Q10 of more than 2.0 demonstrates the absence of endothermy. Chicken embryos aged between 14 and 21 d have a Q10 of less than 2.0 at body temperatures (Taf) between 34 and 30°C. It is postulated that in chicken embryos of this age endothermic reactions may occur. 5. The Q10-method is suitable for investigating the prenatal development of endothermic reactions in avian embryos. 相似文献
11.
1. 1. The superoxide anion radical (O2−) reacts with ferricytochrome c to form ferrocytochrome c. No intermediate complexes are observable. No reaction could be detected between O2− and ferrocytochrome c. 2. 2. At 20 °C the rate constant for the reaction at pH 4.7 to 6.7 is 1.4 · 106 M−1 · s−1 and as the pH increases above 6.7 the rate constant steadily decreases. The dependence on pH is the same for tuna heart and horse heart cytochrome c. No reaction could be demonstrated between O2− and the form of cytochrome c which exists above pH ≈ 9.2. The dependence of the rate constant on pH can be explained if cytochrome c has pKs of 7.45 and 9.2, and O2− reacts with the form present below pH 7.45 with k = 1.4 · 106 M−1 · s−1, the form above pH 7.45 with k = 3.0 · 105 M−1 · s−1, and the form present above pH 9.2 with k = 0. 3. 3. The reaction has an activation energy of 20 kJ mol−1 and an enthalpy of activation at 25 °C of 18 kJ mol−1 both above and below pH 7.45. It is suggested that O2− may reduce cytochrome c through a track composed of aromatic amino acids, and that little protein rearrangement is required for the formation of the activated complex. 4. 4. No reduction of ferricytochrome c by HO2 radicals could be demonstrated at pH 1.2–6.2 but at pH 5.3, HO2 radicals oxidize ferrocytochrome c with a rate constant of about 5 · 105–5 · 106 M−1 · s−1
. 相似文献
12.
Reaction center particles isolated from carotenoidless mutant Rhodopseudomonas spheroides were studied with the aim of determining the pigment composition and the molar extinction coefficients. Two independent sets of measurements using a variety of methods show that a sample with A800 nm = 1.00 contains 20.8 ± 0.8 μM tetrapyrrole and that the ratio of bacteriochlorophyll to bacteriopheophytin is 2:1. Measurements were made of the absorption changes attending the oxidation of cytochrome c coupled to reduction of the photooxidized primary electron donor in reaction centers, using laser flash excitation. The ratio of the absorption change at 865 nm (due to the bleaching of P870) to that at 550 nm (oxidation of cytochrome) was found to be 5.77. These results, combined with other data, yield a pigment composition of 4 bacteriochlorophyll and 2 bacteriopheophytin molecules in a reaction center. Based on this choice, extinction coefficients are determined for the 802- and 865-nm bands: 802 nm = 288 (± 14) mM−1 · cm−1 and 865 nm = 128 (± 6) mM−1 · cm−1. For reversible bleaching of the 865-nm band, Δred - ox865nm = 112 (± 6) mM−1 · cm−1 (referred to the molarity of reaction centers). Earlier reported values of photochemical quantum efficiency are recomputed, and the revised values are shown to be compatible with those obtained from measurements of fluorescence transients. 相似文献
13.
Oxygenation of [Cu II(fla)(idpa)]ClO 4 (fla=flavonolate; IDPA=3,3′-iminobis( N, N-dimethylpropylamine)) in dimethylformamide gives [Cu II(idpa)( O-bs)]ClO 4 ( O-bs= O-benzoylsalicylate) and CO. The oxygenolysis of [Cu II(fla)(idpa)]ClO 4 in DMF was followed by electronic spectroscopy and the rate law −d[{Cu II(fla)(idpa)}ClO 4]/d t= kobs[{Cu II(fla)(idpa)}ClO 4][O 2] was obtained. The rate constant, activation enthalpy and entropy at 373 K are kobs=6.13±0.16×10 −3 M −1 s −1, Δ H‡=64±5 kJ mol −1, Δ S‡=−120±13 J mol −1 K −1, respectively. The reaction fits a Hammett linear free energy relationship and a higher electron density on copper gives faster oxygenation rates. The complex [Cu II(fla)(idpa)]ClO 4 has also been found to be a selective catalyst for the oxygenation of flavonol to the corresponding O-benzoylsalicylic acid and CO. The kinetics of the oxygenolysis in DMF was followed by electronic spectroscopy and the following rate law was obtained: −d[flaH]/d t= kobs[{Cu II(fla)(idpa)}ClO 4][O 2]. The rate constant, activation enthalpy and entropy at 403 K are kobs=4.22±0.15×10 −2 M −1 s −1, Δ H‡=71±6 kJ mol −1, Δ S‡=−97±15 J mol −1 K −1, respectively. 相似文献
14.
1. 1. Cyanide inhibits the catalytic activity of cytochrome aa3 in both polarographic and spectrophotometric assay systems with an apparent velocity constant of 4·103 M−1·s−1 and a Ki that varies from 0.1 to 1.0 μM at 22 °C, pH 7·3. 2. 2. When cyanide is added to the ascorbate-cytochrome c-cytochromeaa3−O2 system a biphasic reduction of cytochrome c occurs corresponding to an initial Ki of 0.8 μM and a final Ki of about 0.1 μM for the cytochrome aa3−cyanide reaction. 3. 3. The inhibited species (a2+a33+HCN) is formed when a2+a33+ reacts with HCN, when a2+a32+HCN reacts with oxygen, or when a3+a33+HCN (cyano-cytochrome aa3) is reduced. Cyanide dissociates from a2+a33+HCN at a rate of 2·10−3 s−1 at 22 °C, pH 7.3. 4. 4. The results are interpreted in terms of a scheme in which one mole of cyanide binds more tightly and more rapidly to a2+a33+ than to a3+a33+.
Abbreviations: TMPD, N,N,N′,N′-tetramethyl-p-phenylenediamine 相似文献
15.
New mixed metal complexes SrCu 2(O 2CR) 3(bdmap) 3 (R = CF 3 (1a), CH 3 (1b)) and a new dinuclear bismuth complex Bi 2(O 2CCH 3) 4(bdmap) 2(H 2O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF 2 and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi 2O 3 at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2 J = 34.0(8) cm −1. Crystal data for 1a: C 27H 51N 6O 9F 9Cu 2Sr/THF, monoclinic space group P2 1/ m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) Å 3, Z = 2; for 1b: C 27H 60N 6O 9Cu 2Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) Å 3, Z = 8; for 2: C 22H 48O 11N 4Bi 2, monoclinic space group P2 1/ c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) Å 3, Z = 4. 相似文献
16.
Treatment of enucleated, granule-free neutrophil cytoplasts with the protein kinase C activator phorbol 12 O-myristate-13-acetate (PMA) causes an increased - 32P-incorporation into a variety of polypeptides. Permeabilization of PMA-stimulated, 32P-labeled cytoplasts by 0.01% digitonin fully releases the majority of these phosphorylated proteins. A statistically significant correlation is found between the extent of PMA-induced activation of generation of Superoxide anion (O −2) and the phosphorylation of a cytosolic polypeptide with an apparent Mr, of 46000, whose - 32P-labeling is also enhanced by the treatment of cytoplasts with 1-oleyl-2-acetylglycerol, the Ca 2+ ionophore ionomycin or latex beads. Furthermore, treatment of cytoplasts with the protein kinase C inhibitor trifluoperazine markedly inhibits the 32P-labeling of proteins in the 40000 Mr range, including the 46 kDa polypeptide, and almost totally abolishes the activation of O −2 production by PMA. 相似文献
17.
Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H 2O 2 induces production of O 2− by activating NADPH oxidase. However, the mechanisms whereby H 2O 2 induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H 2O 2 on O 2− levels on porcine aortic endothelial cells (PAEC). Treatment with 60 μmol/L H 2O 2 markedly increased intracellular O 2− levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O 2− levels and attenuated cytotoxicity resulting from treatment with H 2O 2. L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O 2− levels in PAEC treated with H 2O 2, suggesting that both NOS and NADPH oxidase contribute to H 2O 2-induced O 2− in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O 2− levels in PAEC treated with H 2O 2 to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H 2O 2 produces oxidative stress in endothelial cells by increasing intracellular O 2− levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H 2O 2 and oxidant-generating enzymes that may contribute to endothelial dysfunction. 相似文献
18.
The aqueous chemistry of vanadium with physiologically relevant ligands constitutes a subject of burgeoning research, extending from bacterial metalloenzymic functions to human-health physiology. Vanadium, in the form of VCl 3 and V 2O 5, reacted expediently with citric acid, in a 1:2 molar ratio in water at pH4, and, in the presence of various cations, afforded crystalline materials bearing the general formula (Cat) 2[V 2O 4(C 6H 6O 7) 2]· nH 2O (A) (Cat +=Na +, NH 4 +, n=2; Me 4N +, K +, n=4). Exploration of the reactivity of A toward H 2O 2 yielded the peroxo-containing complexes (Cat) 2[V 2O 2(O 2) 2(C 6H 6O 7) 2]·2H 2O (B) (Cat +=K +, NH 4 +). Both classes of compounds were characterized analytically and spectroscopically. The X-ray structures of complexes A and B emphasize the exceptional stability of the dimeric rhombic unit V V 2O 2, which is retained upon H 2O 2 reaction, and the preserved mode of coordination of the citrate ligand as a doubly deprotonated moiety. In these complexes, typical six and eight coordination numbers were observed for the Na + and K + counter-ions, respectively. The variety of synthetic approaches leading to A, along with the stepwise and direct assembly and isolation of peroxo-compounds (B), denotes the significance of reaction pathways and intermediates in vanadium(III–V)–citrate synthetic chemistry. Hence, a systematic investigation of reactivity modes in aqueous vanadium–citrate systems emerges as a crucial tool for the establishment of chemical interconnectivity among low MW complex species, potentially participating in the intricate biodistribution of that metal ion in biological fluids. 相似文献
19.
Purified NADPH cytochrome c reductase catalyzes the oxidation of NADPH in the presence of Fe 3+, ADP and EDTA. EDTA in this system appears to elevate the redox potential of ferric ion and of its iron complex thereby facilitating the transfer of one electron from NADPH to tri-valent iron (more rapidly than superoxide is formed) through a flavin moiety in the reductase, but it diminishes the concentration of free iron to be required for phospholipid peroxidation. The reduction of Fe3+ by the xanthine-xanthine oxidase system is different from that manifested by the NADPH-NADPH cytochrome c reductase system in the manner in which the former is carried out in the main by Ostaggered2staggered− · generated by the substrate - O2 - enzyme interaction. Reduced iron, which is free in the solution, plays an important role for the initiation and propagation of the phospholipid peroxidation, monitored by malondialdehyde assay and light emission. In the xanthine-induced lipoxygenation system, the ·OH radical, probably produced from hydrogen peroxide by the action of Fe2+, is not involved in the initiation of the peroxidative cleavage of phospholipid in microsomal lipoprotein. 相似文献
20.
The ester cleavage of R- and S-isomers N-CBZ-leucine p-nitrophenyl ester intermolecularly catalyzed by R- (a) and S-stereoisomers (b) of the Pd(II) metallacycle [Pd(C 6H 4C *HMeNMe 2)Cl(py)] (3) follows the rate expression kobs = ko + kcat [3], where the rate constants kcat equal 25.8 ± 0.4 and 7.6 ± 0.5 dm 3 mol −1 s −1 for the S- and R-ester, respectively, in the case of 3a, but are 5.7 ± 0.6 and 26.7 ± 0.5 dm 3 mol −1 s −1 for the S- and R-ester, respectively, in the case of 3b (pH 6.23 and 25°C). Thus, the best catalysis occurs when the asymmetric carbons of the leucine ester and Pd(II) complex are R and S, or S and R configured, respectively. Molecular modeling suggests that the stereoselection results from the spatial interaction between the CH 2CHMe 2 radical of the ester and the -methyl group of 3. A hydrophobic/stacking contact between the leaving 4-nitrophenolate and the coordinated pyridine also seems to play a role. Less efficient intramolecular enantioselection was observed for the hydrolysis of N-t-BOC- S-metthionine p-nitrophenyl ester with R- and S-enantiomers of [Pd(C 6H 4C*HMeNMe 2)Cl] coordinated to sulfur. 相似文献
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