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1.
Eukaryotic H ferritins move iron through protein cages to form biologically required, iron mineral concentrates. The biominerals are synthesized during protein-based Fe2+/O2 oxidoreduction and formation of [Fe3+O]n multimers within the protein cage, en route to the cavity, at sites distributed over ∼50 Å. Recent NMR and Co2+-protein x-ray diffraction (XRD) studies identified the entire iron path and new metal-protein interactions: (i) lines of metal ions in 8 Fe2+ ion entry channels with three-way metal distribution points at channel exits and (ii) interior Fe3+O nucleation channels. To obtain functional information on the newly identified metal-protein interactions, we analyzed effects of amino acid substitution on formation of the earliest catalytic intermediate (diferric peroxo-A650 nm) and on mineral growth (Fe3+O-A350 nm), in A26S, V42G, D127A, E130A, and T149C. The results show that all of the residues influenced catalysis significantly (p < 0.01), with effects on four functions: (i) Fe2+ access/selectivity to the active sites (Glu130), (ii) distribution of Fe2+ to each of the three active sites near each ion channel (Asp127), (iii) product (diferric oxo) release into the Fe3+O nucleation channels (Ala26), and (iv) [Fe3+O]n transit through subunits (Val42, Thr149). Synthesis of ferritin biominerals depends on residues along the entire length of H subunits from Fe2+ substrate entry at 3-fold cage axes at one subunit end through active sites and nucleation channels, at the other subunit end, inside the cage at 4-fold cage axes. Ferritin subunit-subunit geometry contributes to mineral order and explains the physiological impact of ferritin H and L subunits. 相似文献
2.
Tosha T Behera RK Ng HL Bhattasali O Alber T Theil EC 《The Journal of biological chemistry》2012,287(16):13016-13025
Ferritin protein nanocages, self-assembled from four-α-helix bundle subunits, use Fe2+ and oxygen to synthesize encapsulated, ferric oxide minerals. Ferritin minerals are iron concentrates stored for cell growth. Ferritins are also antioxidants, scavenging Fenton chemistry reactants. Channels for iron entry and exit consist of helical hairpin segments surrounding the 3-fold symmetry axes of the ferritin nanocages. We now report structural differences caused by amino acid substitutions in the Fe2+ ion entry and exit channels and at the cytoplasmic pores, from high resolution (1.3–1.8 Å) protein crystal structures of the eukaryotic model ferritin, frog M. Mutations that eliminate conserved ionic or hydrophobic interactions between Arg-72 and Asp-122 and between Leu-110 and Leu-134 increase flexibility in the ion channels, cytoplasmic pores, and/or the N-terminal extensions of the helix bundles. Decreased ion binding in the channels and changes in ordered water are also observed. Protein structural changes coincide with increased Fe2+ exit from dissolved, ferric minerals inside ferritin protein cages; Fe2+ exit from ferritin cages depends on a complex, surface-limited process to reduce and dissolve the ferric mineral. High concentrations of bovine serum albumin or lysozyme (protein crowders) to mimic the cytoplasm restored Fe2+ exit in the variants to wild type. The data suggest that fluctuations in pore structure control gating. The newly identified role of the ferritin subunit N-terminal extensions in gating Fe2+ exit from the cytoplasmic pores strengthens the structural and functional analogies between ferritin ion channels in the water-soluble protein assembly and membrane protein ion channels gated by cytoplasmic N-terminal peptides. 相似文献
3.
New Vistas on the Recruiting of Ferrous Iron and Dioxygen by Ferritins: A Case Study of the Escherichia coli 24‐mer Ferritin by All‐Atom Molecular Dynamics in Aqueous Medium
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Francesco Pietra 《化学与生物多样性》2018,15(8)
It is shown here that Fe2+ and O2 ligands are displaced from the ferroxidase center of the C1 four‐helix bundle of E. coli 24‐mer ferritin under molecular dynamics (MD) aided by a randomly oriented external force applied to the ligand. Under these conditions, ligand egress toward the external aqueous medium occurs preferentially from the same four‐helix bundle, in the case of O2, or other bundle, in the case of Fe2. Viewing ligand egress from the protein as the microscopic reverse of ligand influx into the protein under unbiased MD, these findings challenge current views that preferential gates for recruitment of Fe2+ are 3‐fold channels with human ferritin, or the short path from the ferroxidase center to H93 with bacterial ferritins. 相似文献
4.
Brandon N. Hudder Jessica Garber Morales Audria Stubna Eckard Münck Michael P. Hendrich Paul A. Lindahl 《Journal of biological inorganic chemistry》2007,12(7):1029-1053
Mitochondria from respiring cells were isolated under anaerobic conditions. Microscopic images were largely devoid of contaminants, and samples consumed O2 in an NADH-dependent manner. Protein and metal concentrations of packed mitochondria were determined, as was the percentage of external void volume. Samples were similarly packed into electron paramagnetic resonance tubes, either in the as-isolated state or after exposure to various reagents. Analyses revealed two signals originating from species that could be removed by chelation, including rhombic Fe3+ (g = 4.3) and aqueous Mn2+ ions (g = 2.00 with Mn-based hyperfine). Three S = 5/2 signals from Fe3+ hemes were observed, probably arising from cytochrome c peroxidase and the a3:Cub site of cytochrome c oxidase. Three Fe/S-based signals were observed, with averaged g values of 1.94, 1.90 and 2.01. These probably arise, respectively, from the [Fe2S2]+ cluster of succinate dehydrogenase, the [Fe2S2]+ cluster of the Rieske protein of cytochrome bc 1, and the [Fe3S4]+ cluster of aconitase, homoaconitase or succinate dehydrogenase. Also observed was a low-intensity isotropic g = 2.00 signal arising from organic-based radicals, and a broad signal with g ave = 2.02. Mössbauer spectra of intact mitochondria were dominated by signals from Fe4S4 clusters (60–85% of Fe). The major feature in as-isolated samples, and in samples treated with ethylenebis(oxyethylenenitrilo)tetraacetic acid, dithionite or O2, was a quadrupole doublet with ΔE Q = 1.15 mm/s and δ = 0.45 mm/s, assigned to [Fe4S4]2+ clusters. Substantial high-spin non-heme Fe2+ (up to 20%) and Fe3+ (up to 15%) species were observed. The distribution of Fe was qualitatively similar to that suggested by the mitochondrial proteome. 相似文献
5.
6.
Richard D. Harcourt 《Journal of biological inorganic chemistry》2014,19(1):113-123
For the Fe–O2(S = 0) linkages of oxyhemes, valence bond (VB) structures are re-presented for the McClure [FeII(S = 1) + O2(S = 1)], Pauling–Coryell [FeII(S = 0) + O2*(S = 0)], and Weiss [FeIII(S = ½) + O2 ?(S = ½)] models of bonding. The VB structures for the McClure and Weiss models are of the increased-valence type, with more electrons participating in bonding than occur in their component Lewis structures. The Fe–O bond number and O–O bond order for the McClure structure are correlated with measured Fe–O and O–O bond lengths for oxymyoglobin. Back-bonding from O 2 ? to FeIII of the Weiss structure gives a restricted form of the McClure structure. The McClure and Weiss increased-valence structures are used to provide VB formulations of mechanisms for the oxyhemoglobin + NO reaction. The products of these two formulations are Hb+ and NO3 ? (where Hb is hemoglobin) and Hb+ and OONO?, respectively. Because Hb+ and NO3 ? are the observed products, they provide an experimental procedure for distinguishing the McClure and Weiss models. It is also shown that the same type of agreement between McClure-type theory and experiment occurs for oxycoboglobin + NO, cytochrome P450 monooxygenases, and related hydrogen atom transfer reactions. In the appendices, the results of density functional theory and multireference molecular orbital calculations for oxyhemes are related to one formulation of the increased-valence wavefunction for the McClure model, and theory is presented for the calculation of approximate weights for the Lewis structures that are components of the McClure increased-valence structure. 相似文献
7.
Chih-Yu Huang Yu-Ting Chen Lisa Wen Dey-Chyi Sheu Chi-Tsai Lin 《Molecular biology reports》2014,41(1):155-164
Peroxiredoxins (Prxs) play important roles in antioxidant defense and redox signaling pathways. A Prx isozyme cDNA (TcPrx2, 745 bp, EF552425) was cloned from Taiwanofungus camphorata and its recombinant protein was overexpressed. The purified protein was shown to exist predominantly as a dimer by sodium dodecyl sulfate-polyacrylamide gel electrolysis in the absence of a reducing agent. The protein in its dimeric form showed no detectable Prx activity. However, the protein showed increased Prx activity with increasing dithiothreitol concentration which correlates with dissociation of the dimer into monomer. The TcPrx2 contains two Cys residues. The Cys60 located in the conserved active site is the putative active peroxidatic Cys. The role of Cys31 was investigated by site-directed mutagenesis. The C31S mutant (C31 → S31) exists predominantly as a monomer with noticeable Prx activity. The Prx activity of the mutant was higher than that of the corresponding wild-type protein by nearly twofold at 12 μg/mL. The substrate preference of the mutant was H2O2 > cumene peroxide > t-butyl peroxide. The Michaelis constant (K M) value for H2O2 of the mutant was 0.11 mM. The mutant enzyme was active under a broad pH range from 6 to 10. The results suggest a role of Cys31 in dimerization of the TcPrx2, a role which, at least in part, may be involved in determining the activity of Prx. The C31 residue does not function as a resolving Cys and therefore the TcPrx2 must follow the reaction mechanism of 1-Cys Prx. This TcPrx2 represents a new isoform of Prx family. 相似文献
8.
The scope of this study is to achieve carrier-bound immobilization of catalase onto magnetic particles (Fe3O4 and Fe2O3NiO2 · H2O) to specify the optimum conditions of immobilization. Removal of H2O2 and the properties of immobilized sets were also investigated. To that end, adsorption and then cross-linking methods onto magnetic particles were performed. The optimum immobilization conditions were found for catalase: immobilization time (15 min for Fe3O4; 10 min for Fe2O3NiO2 · H2O), the initial enzyme concentration (1 mg/mL), amount of magnetic particles (25 mg), and glutaraldehyde concentration (3%). The activity reaction conditions (optimum temperature, optimum pH, pH stability, thermal stability, operational stability, and reusability) were characterized. Also kinetic parameters were calculated by Lineweaver–Burk plots. The optimum pH values were found to be 7.0, 7.0, and 8.0 for free enzyme, Fe3O4-immobilized catalases, and Fe2O3NiO2 · H2O-immobilized catalases, respectively. All immobilized catalase systems displayed the optimum temperature between 25 and 35°C. Reusability studies showed that Fe3O4-immobilized catalase can be used 11 times with 50% loss in original activity, while Fe2O3NiO2 · H2O-immobilized catalase lost 67% of activity after the same number of uses. Furthermore, immobilized catalase systems exhibited improved thermal and pH stability. The results transparently indicate that it is possible to have binding between enzyme and magnetic nanoparticles. 相似文献
9.
Chi-Won CHOI Jikhyon HAN Dong-Hwan SEO Jae-Kwan RYU Seock-Yeon HWANG Sook Jae SEO Chi-Young YUN 《Entomological Research》2004,34(1):47-54
Agrius convolvuli haemolymph ferritin was purified by KBr density gradient ultracentrifugation and anion exchange column chromatography. The 670 kDa ferritin was composed of two subunits of 26 kDa and 31 kDa. It was also shown that the protein had an isoelectric point (pI) of pH 7.4. The N‐terminal amino acid sequences of the two subunits were NH2‐DNXYQDVSLDXSQAXNXL (26 kDa subunit) and NH2‐TQXHVNPVNIQRDXVTMHXS (31 kDa subunit). The sequential analysis showed that they had high similarity to lepidopteran ferritin subunits, S‐ and G‐type, respectively. Using electron microscope, it was observed that the protein had a core whose size was about 7 nm. In the amino acid composition of the protein, Glu (13.22%), Asp (10.43%), Pro (9.69%), Leu (9.63%), Ala (9.55%) and Gly (8.49%) were in relatively high contents while Tyr (1.21%), His (2.58%) and Arg (3.10 %) were in low. It was shown that the amount of ferritin in A. convolvuli haemolymph was increased by injection of eight different heavy metal ions, FeCl3, HgCl2, CuSO4, ZnSO4, MnCl2, MgCl2, CrCl3 and CdCl2. Among the ions, Fe3+, Hg2+, Zn4+, Mn2+ and Cd.2+ significantly induced the amount of the protein. 相似文献
10.
Barindra Sana Eric Johnson Pierre Le Magueres Angela Criswell Duilio Cascio Sierin Lim 《The Journal of biological chemistry》2013,288(45):32663-32672
Archaeoglobus fulgidus ferritin (AfFtn) is the only tetracosameric ferritin known to form a tetrahedral cage, a structure that remains unique in structural biology. As a result of the tetrahedral (2-3) symmetry, four openings (∼45 Å in diameter) are formed in the cage. This open tetrahedral assembly contradicts the paradigm of a typical ferritin cage: a closed assembly having octahedral (4-3-2) symmetry. To investigate the molecular mechanism affecting this atypical assembly, amino acid residues Lys-150 and Arg-151 were replaced by alanine. The data presented here shed light on the role that these residues play in shaping the unique structural features and biophysical properties of the AfFtn. The x-ray crystal structure of the K150A/R151A mutant, solved at 2.1 Å resolution, indicates that replacement of these key residues flips a “symmetry switch.” The engineered molecule no longer assembles with tetrahedral symmetry but forms a typical closed octahedral ferritin cage. Small angle x-ray scattering reveals that the overall shape and size of AfFtn and AfFtn-AA in solution are consistent with those observed in their respective crystal structures. Iron binding and release kinetics of the AfFtn and AfFtn-AA were investigated to assess the contribution of cage openings to the kinetics of iron oxidation, mineralization, or reductive iron release. Identical iron binding kinetics for AfFtn and AfFtn-AA suggest that Fe2+ ions do not utilize the triangular pores for access to the catalytic site. In contrast, relatively slow reductive iron release was observed for the closed AfFtn-AA, demonstrating involvement of the large pores in the pathway for iron release. 相似文献
11.
Many pathogenic bacteria are able to survive attack by the host's immune system because of antioxidant systems that mitigate the effects of reactive oxygen species. Dps is a hollow 12-subunit protein nanocage that prevents oxidative damage by oxidizing and sequestering intracellular Fe2+; the resulting Fe3+ forms an iron oxyhydroxide nanoparticle in the cage interior. Charged sites on the protein nanocage create an electrostatic gradient that guides ions through well-defined pores that connect the cage interior with the surrounding solution and toward nucleation sites on the cage interior. In this study, we use all-atom molecular dynamics to simulate the motion of simple cations into the dodecameric cage formed by the Dps protein from Listeria monocytogenes. Ion trajectories are analyzed by using a novel, to our knowledge, genetic algorithm to determine the temporal sequence of ion-protein interactions. Ions enter Dps through well-defined pores at the ferritinlike C3 axes, with negatively-charged residues on the outside of the cage forming a fairly well-defined entrance pathway. This method of trajectory analysis may be broadly applicable in situations where the spatial localization of ions or other small molecules is electrostatically driven by a biomolecule. 相似文献
12.
Debora L. Makino Steven B. Larson Alexander McPherson 《Journal of structural biology》2013,181(1):37-52
The structure of Panicum Mosaic Virus (PMV) was determined by X-ray diffraction analysis to 2.9 Å resolution. The crystals were of pseudo symmetry F23; the true crystallographic unit cell was of space group P21 with a = 411.7 Å, b = 403.9 Å and c = 412.5 Å, with β = 89.7°. The asymmetric unit was two entire T = 3 virus particles, or 360 protein subunits. The structure was solved by conventional molecular replacement from two distant homologues, Cocksfoot Mottle Virus (CfMV) and Tobacco Necrosis Virus (TNV), of ~20% sequence identity followed by phase extension. The model was initially refined with exact icosahedral constraints and then with icosahedral restraints. The virus has Ca++ ions octahedrally coordinated by six aspartic acid residues on quasi threefold axes, which is completely different than for either CfMV or TNV. Amino terminal residues 1–53, 1–49 and 1–21 of the A, B and C subunits, respectively, and the four C-terminal residues (239–242) are not visible in electron density maps. The additional ordered residues of the C chain form a prominent “arm” that intertwines with symmetry equivalent “arms” at icosahedral threefold axes, as was seen in both CfMV and TNV. A 17 nucleotide hairpin segment of genomic RNA is icosahedrally ordered and bound at 60 equivalent sites at quasi twofold A–B subunit interfaces at the interior surface of the capsid. This segment of RNA may serve as a conformational switch for coat protein subunits, as has been proposed for similar RNA segments in other viruses. 相似文献
13.
Gelavizh Barzegar Reza Darvishi Cheshmeh Soltani Mehdi Ahmadi Reza Saeedi Mehrnoosh Abtahi 《Soil & Sediment Contamination》2017,26(5):538-557
In the current study, Fe3O4 NPs were synthesized and used as catalysts in a sono-Fenton-like process for remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil. The effects of operational variables were studied using central composite design (CCD) optimization approach. Results indicated that the effects of H2O2 concentration, Fe3O4 NPs dosage, ultrasonic power and pH were significant for pyrene removal as a contaminant model. In optimum experimental conditions, including H2O2 concentration of 78 mM, Fe3O4 NPs dosage of 18 mM, ultrasonic power of 313 W and pH value of 3.46, the observed pyrene removal was obtained 98.37%, which was verified through the additional experimental tests (99.33%). Pseudo first-order kinetic model was well fitted with the experimental data of pyrene removal with significant coefficient of correlation (R2: 0.9672). Accordingly, an unwashed real soil sample containing diffident PAHs (pyrene, flurene, acenaphthylene, phenenthrene, chrysene, etc) was subjected to sono-Fenton-like process based on optimized conditions. The obtained findings revealed that the removal (%) ranged between 37.7% and 85.19% for different PAHs. 相似文献
14.
Stefan Mebs Ramona Kositzki Jifu Duan Leonie Kertess Moritz Senger Florian Wittkamp Ulf-Peter Apfel Thomas Happe Sven T. Stripp Martin Winkler Michael Haumann 《BBA》2018,1859(1):28-41
[FeFe]-hydrogenases are superior hydrogen conversion catalysts. They bind a cofactor (H-cluster) comprising a four-iron and a diiron unit with three carbon monoxide (CO) and two cyanide (CN?) ligands. Hydrogen (H2) and oxygen (O2) binding at the H-cluster was studied in the C169A variant of [FeFe]-hydrogenase HYDA1, in comparison to the active oxidized (Hox) and CO-inhibited (Hox-CO) species in wildtype enzyme. 57Fe labeling of the diiron site was achieved by in vitro maturation with a synthetic cofactor analogue. Site-selective X-ray absorption, emission, and nuclear inelastic/forward scattering methods and infrared spectroscopy were combined with quantum chemical calculations to determine the molecular and electronic structure and vibrational dynamics of detected cofactor species. Hox reveals an apical vacancy at Fed in a [4Fe4S-2Fe]3 ? complex with the net spin on Fed whereas Hox-CO shows an apical CN? at Fed in a [4Fe4S-2Fe(CO)]3 ? complex with net spin sharing among Fep and Fed (proximal or distal iron ions in [2Fe]). At ambient O2 pressure, a novel H-cluster species (Hox-O2) accumulated in C169A, assigned to a [4Fe4S-2Fe(O2)]3 ? complex with an apical superoxide (O2?) carrying the net spin bound at Fed. H2 exposure populated the two-electron reduced Hhyd species in C169A, assigned as a [(H)4Fe4S-2Fe(H)]3 ? complex with the net spin on the reduced cubane, an apical hydride at Fed, and a proton at a cysteine ligand. Hox-O2 and Hhyd are stabilized by impaired O2– protonation or proton release after H2 cleavage due to interruption of the proton path towards and out of the active site. 相似文献
15.
The effectiveness of the metal oxide nanoparticles viz. CuO and Fe2O3 as antibacterial agents against multidrug resistant biofilm forming bacteria was evaluated. CuO nanoparticles were also experimented for antibiofilm and time kill assay. The CuO displayed maximum antibacterial activity with zone of inhibition of (22 ± 1) mm against methicillin resistant Staphylococcus aureus (MRSA) followed by Escherichia coli (18 ± 1) mm. The Fe2O3 showed the zone of inhibition against MRSA of (14 ± 1) mm followed by E. coli (12 ± 1) mm. CuO proved to be more toxic than Fe2O3 nanoparticles showing significantly high antibacterial activity and found to possess dose dependent antibiofilm properties. 相似文献
16.
Toshiko Miyake Maurizio Bruschi Ugo Cosentino Carole Baffert Vincent Fourmond Christophe Léger Giorgio Moro Luca De Gioia Claudio Greco 《Journal of biological inorganic chemistry》2013,18(6):693-700
[FeFe] hydrogenases are H2-evolving enzymes that feature a diiron cluster in their active site (the [2Fe]H cluster). One of the iron atoms has a vacant coordination site that directly interacts with H2, thus favoring its splitting in cooperation with the secondary amine group of a neighboring, flexible azadithiolate ligand. The vacant site is also the primary target of the inhibitor O2. The [2Fe]H cluster can span various redox states. The active-ready form (Hox) attains the FeIIFeI state. States more oxidized than Hox were shown to be inactive and/or resistant to O2. In this work, we used density functional theory to evaluate whether azadithiolate-to-iron coordination is involved in oxidative inhibition and protection against O2, a hypothesis supported by recent results on biomimetic compounds. Our study shows that Fe–N(azadithiolate) bond formation is favored for an FeIIFeII active-site model which disregards explicit treatment of the surrounding protein matrix, in line with the case of the corresponding FeIIFeII synthetic system. However, the study of density functional theory models with explicit inclusion of the amino acid environment around the [2Fe]H cluster indicates that the protein matrix prevents the formation of such a bond. Our results suggest that mechanisms other than the binding of the azadithiolate nitrogen protect the active site from oxygen in the so-called H ox inact state. 相似文献
17.
Effects of cyclic AMP on the kinetics of serum protein synthesis in cultured mouse hepatoma cells 总被引:1,自引:0,他引:1
The mouse hepatoma cell line, Hepa, was cultured in the presence of either 1 mM N6, O2′-dibutyryl cyclic AMP (Bt2cAMP), 0.5 mM 3-isobutyl-1-methylxanthine, or 1 μg/ml cholera toxin. The synthesis and secretion of albumin, α-fetoprotein, and transferrin were elevated above controls by 24 h reaching two- to fourfold stimulations within 72 h. These effects were reversible and were specific for the serum proteins. The stimulation of serum protein synthesis was accompanied by a decrease in the rate of cell proliferation. Protein synthetic parameters were analyzed in Hepa cells 72 h after exposure to N6,O2′-dibutyryl cyclic AMP. The cellular rate of albumin synthesis was increased fourfold and the relative rate of albumin synthesis was increased approximately threefold. N6,O2′-Dibutyryl cyclic AMP did not affect the size distribution of either total Hepa polyribosomes or of albumin-synthesizing polyribosomes. The elongation rate on total mRNA and on albumin mRNA was decreased by approximately 40%. These results indicate that the rate of initiation of total Hepa mRNA and of albumin mRNA also decreased by 40%. The nonspecific nature of the N6,O2′-dibutyryl cyclic AMP effect on Hepa protein synthetic parameters must be due to an alteration in the level of a common substrate, perhaps ATP. The specific threefold increase in the relative rate of albumin synthesis with no alteration in polyribosome sizes requires a threefold increase in the relative amount of functional albumin mRNA in Hepa cells. This prediction was confirmed by cell-free translation of Hepa polyribosomes. 相似文献
18.
S. Hena N. Fatihah S. Tabassum J. Lalung S. Y. Jing 《Journal of applied phycology》2016,28(3):1597-1609
A magnetophoretic harvesting agent, a polypyrrole/Fe3O4 magnetic nanocomposite, is proposed as a cost and energy efficient alternative to recover biomass of the microalgae Botryococcus braunii, Chlorella protothecoides, and Chlorella vulgaris from their culture media. The maximal recovery efficiency reached almost 99 % for B. braunii, 92.4 % for C. protothecoides, and 90.8 % for C. vulgaris. The maximum adsorption capacity (Q 0) of the magnetic nanocomposite for B. braunii (63.49 mg dry biomass mg?1 PPy/Fe3O4) was higher than that for C. protothecoides (43.91 mg dry biomass mg?1 PPy/Fe3O4) and C. vulgaris (39.98 mg dry biomass mg?1 PPy/Fe3O4). The highest harvesting efficiency for all the studied microalgae were at pH 10.0, and measurement of zeta-potential confirmed that the flocculation was induced by charge neutralization. This study showed that polypyrrole/Fe3O4 can be a promising flocculant due to its high efficacy, low dose requirements, short settling time, its integrity with cells, and with great potential for saving energy because of its recyclability. 相似文献
19.
Construction of a ferritin reactor: an efficient means for trapping various heavy metal ions in flowing seawater 总被引:2,自引:0,他引:2
An apparatus consisting of two pumps, a mixer, a ferritin reactor, and a spectrophotometer was constructed to study the ability to trap various heavy metal ions (M2+) and the dynamics of a reconstituted ferritin reactor in flowing seawater. Reconstituted pig spleen ferritin (PSFr) is assembled from apo-protein shell to form a reconstituted iron core. The main components of the PSFr are its core, which contains an Fe2+:Pi stoichiometry of 6.0±0.5, reconstituted from pig spleen apoferritin (apo PSF), Fe2+, inorganic phosphate (Pi), and O2 (0.6 atm). The Fe3+—Pi clusters within the PSFr core exhibit resistance to salt ranging from 1% to 6% NaCl. The ferritin reactor consists of PSFr and an oscillating bag. Using the reactor, M2+ ions such as Cd2+, Zn2+, Co2+, and Mn2+ are directly trapped by the ferritin. We found a 1:2±0.2 stoichiometry of the trapped M2+ to the released iron as measured by chemical analysis or atomic absorption spectrometry; nontransient elements such as Na+, K+, Ca2+, etc., were scarcely trapped by the reactor. This study provides basic conditions for establishing a ferritin reactor and a convenient means for monitoring the pollution of heavy metal ions in seawater. 相似文献
20.
Donald M. Kurtz Jr. 《Journal of biological inorganic chemistry》1997,2(2):159-167
Diiron-oxo proteins currently represent one of the most rapidly developing areas of bioinorganic chemistry. All of these
proteins contain a four-helix bundle protein fold surrounding a (μ-carboxylato)diiron core, and most, if not all, of the diiron(II)
sites appear to react with O2 as part of their functional processes. Despite these common characteristics, an emerging functional diversity is one of the
most striking aspects of this class of proteins. X-ray crystal structures of diiron(II) sites are now available for four of
these proteins: hemerythrin (Hr), the hydroxylase protein of methane monooxygenase (MMOH), the R2 protein of Escherichia coli ribonucleotide reductase (RNR-R2), and a plant acyl-carrier protein Δ9-desaturase. The structure of the diiron(II) site in Hr, the sole O2 carrier in the group, is clearly distinct from the other three, whose function is oxygen activation. The Hr diiron site is
more histidine rich, and the oxygen-activating diiron sites contain a pair of (D/E)X30–37EX2H ligand sequence motifs, which is clearly not found in Hr. The Hr diiron site apparently permits only terminal O2 coordination to a single iron, whereas the oxygen-activating diiron(II) centers present open or labile coordination sites
on both irons of the center, and show a much greater coordinative flexibility upon oxidation to the diiron(III) state. Intermediates
at the formal FeIIIFeIII and FeIVFeIV oxidation levels for MMOH and formal FeIIIFeIV oxidation level for RNR-R2 have been identified during reactions of the diiron(II) sites with O2. An [Fe2(μ-O)2]4+, 3+ "diamond core" structure has been proposed for the latter two oxidation levels. The intermediate at the FeIIIFeIV oxidation level in RNR-R2 is kinetically competent to generate a stable, functionally essential tyrosyl radical. The FeIVFeIV oxidation level is presumed to effect hydroxylation of hydrocarbons in MMOH, but the mechanism of this hydroxylation, particularly
the involvement of discrete radicals, is currently controversial. The biological function of diiron sites in three members
of this class, rubrerythrin, ferritin and bacterioferritin, remains enigmatic.
Received: 31 July 1996 / Accepted: 4 October 1996 相似文献