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1.
The present work deals with the biosorption performance of raw and chemically modified biomass of the brown seaweed Lobophora variegata for removal of Cd(II) and Pb(II) from aqueous solution. The biosorption capacity was significantly altered by pH of the solution
delineating that the higher the pH, the higher the Cd(II) and Pb(II) removal. Kinetic and isotherm experiments were carried
out at the optimal pH 5.0. The metal removal rates were conspicuously rapid wherein 90% of the total sorption occurred within
90 min. Biomass treated with CaCl2 demonstrated the highest potential for the sorption of the metal ions with the maximum uptake capacities i.e. 1.71 and 1.79 mmol g−1 for Cd(II) and Pb(II), respectively. Kinetic data were satisfactorily manifested by a pseudo-second order chemical sorption
process. The process mechanism consisting of both surface adsorption and pore diffusion was found to be complex. The sorption
data have been analyzed and fitted to sorption isotherm of the Freundlich, Langmuir, and Redlich–Peterson models. The regression
coefficient for both Langmuir and Redlich–Peterson isotherms were higher than those secured for Freundlich isotherm implying
that the biosorption system is possibly monolayer coverage of the L. variegata surface by the cadmium and lead ions. FT-IR studies revealed that Cd(II) and Pb(II) binding to L. variegata occurred primarily through biomass carboxyl groups accompanied by momentous interactions of the biomass amino and amide groups.
In this study, we have observed that L. variegata had maximum biosorption capacity for Cd(II) and Pb(II) reported so far for any marine algae.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
Speciation studies of Co(II), Ni(II) and Cu(II) complexes of L-valine in acetonitrile–water mixtures
《Chemical Speciation and Bioavailability》2013,25(4):258-264
AbstractChemical speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-valine in 0.0-60.0% v/v acetonitrile-water mixtures was studied pH-metrically at an ionic strength of 0.16 mol L-1 at 303.0 K. The existence of different binary complexes was established from the modelling studies, using the computer program MINIQUAD75. The appropriateness of the model was ascertained by studying the effect of errors in concentrations of the reagents. The trend in variation of stability constants with change in the permittivity of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution diagrams and the plausible equilibria for the formation of the species are also presented. 相似文献
3.
N-Salicyloyl-N-p-hydroxythiobenzohydrazide (H2STPH) and N-benzoyl-N-thiobenzohydrazide (H2BTBH) and their Co(II), Ni(II), Cu(II) and Zn(II) complexes were prepared and characterized by physicochemical studies. IR and NMR spectral studies imply dibasic tetradentate behaviour of the ligands bonding through `thiolato' sulfur, enolic oxygen and the two hydrazinic nitrogens in a polymeric fashion. The electronic spectra indicate [Ni(STPH)(H2O)2], [Co(STPH)(H2O)2] to be distorted octahedral while [Cu(BTBH)] has a square-planar geometry. In vitro antitumor results of the ligand and the complexes on P-815 (murine mastocytoma) and L-929 (murine fibroblast) indicate that these compounds show significant inhibition of 3H-thymidine and 3H-uridine incorporation in DNA and RNA, respectively, in these tumor cells at dose levels of 1, 2.5 and 5 g cm–3. Antitumor studies suggest that [Cu(BTBH)] has significant dose dependent inhibitory effect on DNA synthesis. In vivo administration of [Cu(BTBH)] and [Ni(STPH)(H2O)2] resulted into prolongation of life span of Dalton's Lymphoma (DL) bearing mice. 相似文献
4.
Yong Peng Chengshan Wang Howard H. Xu Feimeng Zhou 《Journal of inorganic biochemistry》2010,104(4):365-675
Parkinson’s disease (PD) is hallmarked by the abnormal intracellular inclusions (Lewy bodies or LBs) in dopaminergic cells. Amyloidogenic protein α-synuclein (α-syn) and iron (including both Fe(III) and Fe(II)) are both found to be present in LBs. The interaction between iron and α-syn might have important biological relevance to PD etiology. Previously, a moderate binding affinity between α-syn and Fe(II) (5.8 × 103 M−1) has been measured, but studies on the binding between α-syn and Fe(III) have not been reported. In this work, electrospray mass spectrometry (ES-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were used to study the binding between α-syn and Fe(II) and the redox property of the resultant α-syn-Fe(II) complex. The complex is of a 1:1 stoichiometry and can be readily oxidized electrochemically and chemically (by O2) to the putative α-syn-Fe(III) complex, with H2O2 as a co-product. The reduction potential was estimated to be 0.025 V vs. Ag/AgCl, which represents a shift by −0.550 V vs. the standard reduction potential of the free Fe(III)/Fe(II) couple. Such a shift allows a binding constant between α-syn and Fe(III), 1.2 × 1013 M−1, to be deduced. Despite the relatively high binding affinity, α-syn-Fe(III) generated from the oxidation of α-syn-Fe(II) still dissociates due to the stronger tendency of Fe(III) to hydrolyze to Fe(OH)3 and/or ferrihydrite gel. The roles of α-syn and its interaction with Fe(III) and/or Fe(II) are discussed in the context of oxidative stress, metal-catalyzed α-syn aggregation, and iron transfer processes. 相似文献
5.
Boll M Fuchs G Meier C Trautwein A Lowe DJ 《The Journal of biological chemistry》2000,275(41):31857-31868
Benzoyl-CoA reductase catalyzes the two-electron transfer from a reduced ferredoxin to the aromatic ring of benzoyl-CoA; this reaction is coupled to stoichiometrical ATP hydrolysis. A very low reduction potential (less than -1 V) is required for the first electron transfer to the aromatic ring. In this work the nature of the redox centers of purified benzoyl-CoA reductase from Thauera aromatica was studied by EPR and M?ssbauer spectroscopy. The results obtained indicated the presence of three [4Fe-4S] clusters. Redox titration studies revealed that the reduction potentials of all three clusters were below -500 mV. The previously reported S = 7/2 state of the enzyme during benzoyl-CoA-independent ATPase activity (Boll, M., Albracht, S. J. P., and Fuchs, G. (1997) Eur. J. Biochem. 244, 840-851) was confirmed by M?ssbauer spectroscopy. Inactivation by oxygen was associated with the irreversible conversion of part of the [4Fe-4S] clusters to [3Fe-4S] clusters. Acetylene stimulated the benzoyl-CoA-independent ATPase activity and induced novel EPR signals with g(av) >2. The presence of simple cubane clusters in benzoyl-CoA reductase as the sole redox-active metal centers demonstrates novel aspects of [4Fe-4S] clusters since they adopt the role of elemental sodium or lithium which are used as electron donors in the analogous chemical Birch reduction of aromatic rings. 相似文献
6.
Nathaniel J. Cosper Christina M. V. Stålhandske Ruth E. Saari Robert P. Hausinger R. A. Scott 《Journal of biological inorganic chemistry》1999,4(1):122-129
The first step in the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by Ralstonia eutropha JMP134 is catalyzed by the α-ketoglutarate (α-KG)-dependent dioxygenase TfdA. Previously, EPR and ESEEM studies on inactive
Cu(II)-substituted TfdA suggested a mixture of nitrogen/oxygen coordination with two imidazole-like ligands. Differences between
the spectra for Cu TfdA and α-KG- and 2,4-D-treated samples were interpreted as a rearrangement of the g–tensor principal axis system. Herein, we report the use of X-ray absorption spectroscopy (XAS) to further characterize the
metal coordination environment of Cu TfdA as well as that in the active, wild-type Fe(II) enzyme. The EXAFS data are interpreted
in terms of four N/O ligands (two imidazole-like) in the Cu TfdA sample and six N/O ligands (one or two imidazole-like) in
the Fe TfdA sample. Addition of α-KG results in no significant structural change in coordination for Cu or Fe TfdA. However,
addition of 2,4-D results in a decrease in the number of imidazole ligands in both Cu and Fe TfdA. Since this change is seen
both in the Fe and Cu EXAFS, loss of one histidine ligand upon 2,4-D addition best describes the phenomenon. These XAS data
clearly demonstrate that changes occur in the atomic environment of the metallocenter upon substrate binding.
Received: 3 July 1998 / Accepted: 13 October 1998 相似文献
7.
T A Kent M H Emptage H Merkle M C Kennedy H Beinert E Münck 《The Journal of biological chemistry》1985,260(11):6871-6881
Active beef heart aconitase contains a [4Fe-4S] cluster. One iron of the cluster, Fea, is labile and can be removed easily by oxidation in air to yield the [3Fe-4S]1+ cluster of inactive aconitase. We have previously shown that substrate binds to Fea. We have continued our M?ssbauer studies by further investigating the active and inactive forms of the enzyme. When active aconitase, [4Fe-4S]2+, is mixed with substrate, two species (substrates or intermediates bound to Fea) labeled S1 and S2 are obtained. With the nitroanalogs of citrate and isocitrate, thought to be transition state analogs, and fluorocitrate, species S2, but not S1, is observed, suggesting that S2 represents a carbanion transition state complex. We have prepared M?ssbauer samples by rapid mix/rapid freeze techniques. Using either citrate, isocitrate or cis-aconitate, the natural substrates, we have been able to detect at 0 degree C reaction intermediates in the 5-35 ms time range and, studying enzyme substrate interactions at subzero temperatures in a water/methanol/ethylene glycol solvent, we have observed new species when substrates were added at -60 degrees C. Details of these experiments are given, although in neither case can unique interpretations be offered at this time. We have also investigated reduced active aconitase ([4Fe-4S]1+; EPR at g = 1.94) in the presence of substrate with material selectively enriched with 57Fe in either Fea or the other three cluster sites. The spectra were analyzed with a spin Hamiltonian, and the results are discussed and interpreted in terms of three inequivalent Fe sites in the cluster. Finally, we have studied enzyme containing the reduced [3Fe-4S]0 cluster. There is no indication that citrate binds to the 3Fe cluster, and since no significant activity was observed, we conclude that aconitase containing a 3Fe cluster is not active in either oxidation state. 相似文献
8.
《Inorganica chimica acta》1987,131(1):95-99
The platinum(II) complexes of the formula [Pt(DCHEDA)X2], where DCHEDA is N,N′-dicyclohexylethylenediamine and X− is CL−, Br−, I−, 0.5C2O42− (oxalate), 0.5C3H2O42− (malonate), 0.5C9H4O62− (4-carboxyphthalate), 0.5S2O32− or 0.5SO42−, have been synthesized and characterized by UVVis, IR, and 1H NMR spectral techniques. All the above complexes are non-electrolytes in DMF/H2O, except the sulphate complex which becomes a 1:1 electrolyte after incubation for 24 h at 28 °C. The halide complexes were also studied by X-ray photoelectron spectroscopy and these data suggest that there is π-bonding from platinum to halide in these complexes. The oxalate, malonate and sulphate bind in their complexes as bidentate ligands to platinum through two oxygen atoms whereas the thiosulphate in its complex binds as a bidentate ligand to platinum through one oxygen atom and one sulphur atom. 相似文献
9.
EPR and M?ssbauer studies of protocatechuate 4,5-dioxygenase. Characterization of a new Fe2+ environment 总被引:4,自引:0,他引:4
D M Arciero J D Lipscomb B H Huynh T A Kent E Münck 《The Journal of biological chemistry》1983,258(24):14981-14991
Protocatechuate 4,5-dioxygenase from Pseudomonas testosteroni has been purified to homogeneity and crystallized. The iron containing, extradiol dioxygenase is shown to be composed of two subunit types (alpha, Mr = 17,700 and beta, Mr = 33,800) in a 1:1 ratio; such a composition has not been observed for other extradiol dioxygenases. The 4.2 K M?ssbauer spectrum of native protocatechuate 4,5-dioxygenase prepared from cells grown in 57Fe-enriched media consists of a doublet with quadrupole splitting, delta EQ = 2.22 mm/s, and isomer shift delta Fe = 1.28 mm/s, demonstrating a high spin Fe2+ site. These parameters, and the temperature dependence of delta EQ, are unique among enzymes but are strikingly similar to those reported for the reaction center of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26, suggesting very similar ligand environments. The Fe2+ of protocatechuate 4,5-dioxygenase can be oxidized, for instance by H2O2, to yield high spin Fe3+ with EPR g values around g = 6 (and g = 4.3). In the oxidized state, protocatechuate 4,5-dioxygenase is inactive; the iron, however, can be rereduced by ascorbate to yield active enzyme. Our data suggest that protocatechuate binds to Fe2+; the spectra indicate that the ligand binding is heterogenous. The M?ssbauer spectra observed here are fundamentally different from those reported earlier (Zabinski, R., Münck, E., Champion, P., and Wood, J. M. (1972) Biochemistry 11, 3212-3219). The spectra of the earlier (reconstituted) preparations, which had substantially lower specific activities, probably reflect adventitiously bound Fe3+. We discuss here how adventitiously bound iron can be identified and removed. The Fe2+ which is present in native protocatechuate 4,5-dioxygenase and its complexes with substrates and inhibitors reacts quantitatively with nitric oxide to produce a species with electronic spin S = 3/2. The EPR and M?ssbauer spectra of these complexes compare favorably with EDTA . Fe(II) . NO. We have studied the latter complex extensively and have analyzed the M?ssbauer spectra with an S = 3/2 spin Hamiltonian. EPR spectra show that protocatechuate 4,5-dioxygenase-NO complexes with substrates or inhibitors are heterogeneous and consist of several well defined subspecies. The data show that NO, and presumably also O2, has access to the active site Fe2+ in the enzyme-substrate complex. The use of EPR-detectable NO complexes as a rapid and sensitive tool for the study of the EPR silent active site iron of extradiol dioxygenases is discussed. 相似文献
10.
The equimolar reaction of a β-diketiminate lithium salt LLi(OEt2) [L = HC(CMeNAr)2; Ar = 2,6-iPr2C6H3] with either GeBr2 or SnBr2 in diethyl ether affords the synthetically useful monomeric β-diketiminate-element halides LGeBr (1) and LSnBr (2), respectively. Both are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction analysis. 相似文献
11.
Ch. Nageswara Rao Bogi Srinu V. Gowri Kumari 《Chemical Speciation and Bioavailability》2016,28(1-4):66-71
Chemical speciation of binary complexes of Pb(II) and Cd(II) ions with maleic acid have been studied pH metrically in the concentration range of 0–50% v/v ethylene glycol (EG)–water mixtures maintaining an ionic strength of 0.16 molL?1 at 303 K. Alkalimetric titrations were carried out in different relative concentrations of metal and maleic acid. Stability constants of various models of binary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected are ML2, ML3, and ML2H for Pb(II) and Cd(II). The chemical speciation, metal bioavailability, and transportation are explained based on the distribution diagrams. 相似文献
12.
Kumaraswamy R Kuenen JG Kleerebezem R van Loosdrecht MC Muyzer G 《Applied microbiology and biotechnology》2006,73(4):922-931
BioDeNOx is a combined physicochemical and biological process for the removal of nitrogen oxides (NOx) from flue gas. In the present study, two anaerobic bioreactors performing BioDeNOx were run consecutively (RUN-1 and RUN-2) at a dilution rate of 0.01 h−1 with Fe(II)EDTA.NO2− and Fe(III)EDTA− as electron acceptors and ethanol as electron donor. The measured protein concentration of the reactor biomass of both runs was 120 mg/l. Different molecular methods were used to determine the identity and abundance of the bacterial populations in both bioreactors. Bacillus azotoformans strain KT-1 was recognized as a key player in Fe(II)EDTA.NO2− reduction. PCR-denaturing gradient gel electrophoresis analysis of the reactor biomass showed a greater diversity in RUN-2 than in RUN-1. Enrichments of Fe(II)EDTA.NO2− and Fe(III)EDTA− reducers and activity assays were conducted using the biomass from RUN-2 as an inoculum. The results on substrate turnover, overall microbial diversity, and enrichments and finally activity assays confirmed that ethanol was used as electron donor for Fe(II)EDTA.NO2− reduction. In addition, the Fe(III)EDTA− reduction rate of the microbial community proved to be feasible enough to run the bioreactors, ruling out the chemical reduction of Fe(III)EDTA− with sulfide as was proposed by other researchers. 相似文献
13.
Andreas W. E. Dilg Francesco Capozzi Matthias Mentler Olga Iakovleva Claudio Luchinat Ivano Bertini Fritz G. Parak 《Journal of biological inorganic chemistry》2001,6(3):232-246
M?ssbauer, 57Fe ENDOR, CW and pulsed EPR experiments were performed on the reduced and the oxidized high-potential iron proteins (HiPIPs) of the wild type (WT) and the C77S mutant from Chromatium vinosum. The EPR spectra of the oxidized WT and mutant show three species respectively having nearly the same g-values but strongly changed spectral contributions. Relaxation times were estimated for oxidized WT and mutant at T = 5 K with pulsed EPR. A-tensor components of both iron pairs were obtained by 57Fe ENDOR, proving a similar magnetic structure for the WT and the mutant. Electronic relaxation has to be taken into account at T = 5 K in native and mutated oxidized HiPIPs to achieve agreement between M?ssbauer and 57Fe ENDOR spectroscopies. The M?ssbauer spectroscopy shows that the oxidized cluster contains a pure ferric and a mixed-valence iron pair coupled antiparallel. While all cluster irons from reduced C. vinosum WT are indistinguishable in the M?ssbauer spectrum, the reduced C77S mutant shows a non-equivalence between the serine-bound and the three cysteine-ligated iron ions. The M?ssbauer parameters confirm a loss of the covalent character of the iron bond when S is replaced by O and indicate a shift of the cluster's electron cloud towards the serine. M?ssbauer spectra of the oxidized mutant can be simulated with two models: model I introduces a single electronic isomer with the serine always ligated to a ferric iron. Model II assumes two equally populated electronic isomers with the serine ligated to a ferric iron and a mixed-valence iron, respectively. The latter model is in better agreement with EPR and NMR. 相似文献
14.
Yun Li Nana Wang Dong Lin Xiaohui Liu Yong Yang 《Journal of biomolecular structure & dynamics》2020,38(17):4977-4996
AbstractTwo new nickel (II) triphenylphosphine complexes derived from tridentate aroylhydrazone ligands [H2L1 = 2-hydroxy-3-methoxybenzylidene)benzohydrazone and H2L2 = N′-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone] and triphenylphosphine were prepared and their molecular structures were determined by single crystal X-ray diffraction analysis. Both nickel(II) complexes showed slightly distorted square planar geometry with one tridentate aroylhydrazone ligand coordinated through ONO donor atoms and one triphenylphosphine ligand coordinated to the nickel center through the phosphorus atom. DNA interaction studies indicated that both complexes possessed higher affinity to herring sperm DNA (HS-DNA) than the corresponding free aroylhydrazone ligand. Molecular docking investigations showed that both complexes could bind to DNA through intercalation of the phenyl rings between adjacent base pairs in the double helix. Meanwhile, bovine serum albumin (BSA) binding studies revealed the complexes could effectively interact with BSA and change the secondary structure of BSA. Further pharmacological evaluations of the synthesized complexes by in vitro antioxidant assays demonstrated high antioxidant activity against NO· and O2˙? radicals. The anticancer activity of each complex was assessed through in vitro cytotoxicity assays (CCK-8 kit) toward A549 and MCF-7 cancer cell and normal L-02 cell lines. Significantly, the Ni(II) complex derived from H2L1 ligand was found to be more effective cytotoxic toward MCF-7cancerous cell with the IC50 value equaled 9.7?μM, which showed potent cytotoxic activity over standard drug cisplatin. Abbreviations A549 human lung carcinoma cell BSA bovine serum albumin CCK-8 Cell Counting Kit-8 DFT density functional theory DNA deoxyribonucleic acid DPPH˙ 2,2-diphenyl-1-picrylhydrazyl H2L1 2-hydroxy-3-methoxybenzylidene)benzohydrazone N′-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone H2L2 N′-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone HOMO highest occupied molecular orbital IC50 the 50% activity L-02 human normal liver cell LOMO lowest unoccupied molecular orbital (LUMO) MCF-7 human breast carcinoma cell NO˙ nitric oxide O2˙? superoxide anion SOD superoxide dismutase Communicated by Ramaswamy H. Sarma 相似文献
15.
Agnieszka Krogul Jakub Cedrowski Katarzyna Wiktorska Wojciech P. Oziminski Jadwiga Skupińska Grzegorz Litwinienko 《Bioorganic & medicinal chemistry letters》2013,23(9):2765-2768
Due to the similarity between Pd and Pt, the complexes of palladium(II) can be considered as potential anticancer agents. Activity of six PdCl2(X2Py)2 complexes (Py = pyridine, and X = CH3 or Cl) was measured by MTT test using MCF7, CCRF-SB, PC3 and human B-lymphoblastoid cell lines. We found that the effect of PdCl2(XnPy)2 was cell-specific and time-dependent. Obtained results were discussed and compared with the activation parameters calculated for the hydrolysis of PdCl2(XnPy)2, indicating a correlation between viability of MCF7 and CCRF-SB cells and rates of hydrolysis of the Pd(II) complexes. 相似文献
16.
A new ligand N-Nicotinoyl-N-o-hydroxythiobenzhydrazide (H2Notbh) forms complexes [Mn(Notbh)(H2O)], [M(Notbh)] [M=Ni(II) Cu(II) and Zn(II)] which were characterized by various physico-chemical techniques. All the metal complexes were observed to inhibit the growth of tumor in vitro, whereas, ligand did not. In vivo administration of these complexes resulted in prolongation of survival of tumor bearing mice. Tumor bearing mice administered with metal complexes showed reversal of tumor growth associated induction of apoptosis in lymphocytes. The paper discusses the possible mechanisms and therapeutic implication of the H2Notbh and its metal complexes in tumor regression and tumor growth associated immunosuppression. 相似文献
17.
Werner J. Geldenhuys Nicholas Novotny Sarel F. Malan Cornelis J. Van der Schyf 《Bioorganic & medicinal chemistry letters》2013,23(6):1707-1711
Pentacycloundecylamine (PCU) derived compounds have been shown to be promising lead structures for the development of novel drug candidates aimed at a variety of neurodegenerative and psychiatric diseases. Here we show for the first time a 3D quantitative structure–activity relationship (3D-QSAR) for a series of aza-PCU-derived compounds with activity at the sigma-1 (σ1) receptor. A comparative molecular field analysis (CoMFA) model was developed with a partial least squares cross validated (q2) regression value of 0.6, and a non-cross validated r2 of 0.9. The CoMFA model was effective at predicting the sigma-1 activities of a test set with an r2 >0.7. We also describe here the docking of the PCU-derived compounds into a homology model of the sigma-1 (σ1) receptor, which was developed to gain insight into binding of these cage compounds to the receptor. Based on docking studies we evaluated in a [3H]pentazocine binding assay an oxa-PCU, NGP1-01 (IC50 = 1.78 μM) and its phenethyl derivative (IC50 = 1.54 μM). Results from these studies can be used to develop new compounds with specific affinity for the sigma-1(σ1) receptor. 相似文献
18.
The stepwise 57Fe(II)-thiolate cluster formation in rabbit liver metallothionein-2 (MT) has been followed at pH 8.5 using M?ssbauer spectroscopy. The zero-field spectra recorded at 4.2 K exhibit at all stages of filling one virtually identical single quadrupole splitting delta EQ and isomer shift delta as found for reduced rubredoxin (Rdred) or the model compound [Fe(II)(SPh)4]2-, thus indicating an Fe(II)-tetrathiolate coordination. A similar conclusion was reached also in previous electronic absorption studies [M. Good and M. Vasák (1986) Biochemistry 25,8353--8356]. The M?ssbauer spectra obtained in the presence of a magnetic field were analyzed on the basis of a spin-Hamiltonian formalism resulting in M?ssbauer parameters similar to those for Rdred and the inorganic model compound [Fe(II)(SPh)4]2-. The identity of the M?ssbauer parameters of partially and fully metal-occupied MT suggests that a comparable distortion of the metal binding sites must exist. Simulation of the spectra revealed that the Fe(II) ions in the partially metal-occupied 57Fe(II)4-MT form appear to be magnetically isolated, whereas in the fully metal-saturated 57Fe(II)7-MT form a ratio of 3:4 of paramagnetic to diamagnetic subspectra was obtained. The latter result suggests the existence of three isolated metal binding sites and a metal-thiolate cluster containing four metal ions. In the light of structure determinations of MT containing Zn(II) and/or Cd(II) [W. Braun et al. (1986) J. Mol. Biol. 187, 125-129, and W. F. Furrey et al. (1986) Science (Wash. DC) 231, 704-710], which revealed two metal-thiolate clusters containing three and four metal ions, respectively, and involving all 20 cysteine residues in metal binding, the appearance of M?ssbauer parameters characteristic of three isolated Fe(II) sites in 57Fe(II)7-MT is peculiar and deserves further studies. It is concluded, moreover, that the four-metal cluster is diamagnetic with the four Fe(II) ions being antiferromagnetically coupled. The appearance of magnetic coupling above four Fe(II) equivalents bound to apoMT indicates that the cluster formation occurs in a two-step process. 相似文献
19.
A. W. E. Dilg Giovanna Mincione Klaus Achterhold Olga Iakovleva Matthias Mentler Claudio Luchinat Ivano Bertini F. G. Parak 《Journal of biological inorganic chemistry》1999,4(6):727-741
4 S4]3 + and the reduced [Fe4S4]2 + clusters in the high-potential iron protein I from Ectothiorhodospira halophila were measured in a temperature range from 5 K to 240 K. EPR measurements and 57Fe electron-nuclear double resonance (ENDOR) experiments were carried out with the oxidized protein. In the oxidized state
the cluster has a net spin S = 1/2 and is paramagnetic. As common in [Fe4S4]3 + clusters, the M?ssbauer spectrum was simulated with two species contributing equally to the absorption area: two Fe3 + atoms couple to the “ferric-ferric” pair, and one Fe2 + and one Fe3 + atom give the “ferric-ferrous pair”. For the simulation of the M?ssbauer spectrum, g-values were taken from EPR measurements. A-tensor components were determined by 57Fe ENDOR experiments that turned out to be a necessary source of estimating parameters independently. In order to obtain a
detailed agreement of M?ssbauer and ENDOR data, electronic relaxation has to be taken into account. Relaxing the symmetry
condition in a way that the electric field gradient tensor does not coincide with g- and A-tensors yielded an even better agreement of experimental and theoretical M?ssbauer spectra. Spin-spin and spin-lattice relaxation
times were estimated by pulsed EPR; the former turned out to be the dominating mechanism at T = 5 K. Relaxation times measured by pulsed EPR and obtained from the M?ssbauer fit were compared and yield nearly identical
values. The reduced cluster has one additional electron and has a diamagnetic (S = 0) ground state. All the four irons are indistinguishable in the M?ssbauer spectrum, indicating a mixed-valence state of
Fe2.5 + for each.
Received: 15 February 1999 / Accepted: 31 August 1999 相似文献
20.
The coordination cage of the metal center in Fe(II)-bleomycin has been proposed to consist of the secondary amines in β-aminoalanine, the pyrimidinylpropionamide and imidazole rings, and the amide nitrogen in β-hydroxyhistidine as equatorial ligands, and the primary amine in β-aminoalanine and either the carbamoyl group in mannose or a solvent molecule occupying the axial sites. With the aim of supporting or not supporting coordination of a water molecule to the metal center in Fe(II)-bleomycin, the solution structure of Fe(II)-azide-bleomycin has been derived from NMR data. The structural changes that occur in Fe(II)-bleomycin upon azide binding have been monitored by comparing the experimental results with those obtained from the calculated structures for both bleomycin adducts. The results of this investigation strongly support a model of Fe(II)-bleomycin with six endogenous ligands as the most likely structure held in solution by this metallobleomycin in the absence of DNA. 相似文献