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1.
Bassam M. Nakhle Tracie L. Vestal Matthew J. Saderholm Bruce W. Erickson 《Letters in Peptide Science》1999,6(1):33-43
This paper describes the engineering of braced tripod proteins for use as molecular frameworks. Specifically, a 30-residue tripod-shaped protein with three proline-II helical legs braced by an iron(II)tris(bipyridine) complex was modularly designed, chemically synthesized, and biophysically characterized. Three copies of a 10-residue leg peptide were covalently linked through sulfide bonds to an N-terminal apex (1,3,5-tris(methylene)benzene) and by amide bonds to the brace (FeII(Mbc)3: Mbc is 4-methyl-2,2-bipyridine-4-carbonyl). The leg peptide (H-Cys-Pro5-Pra(Mbc)-Pro3-NH2: Pra is cis-4-amino-l-proline) was assembled by the solid-phase method using Boc-Pra(Mbc)-OH, which was synthesized in 75% overall yield by coupling Mbc-OH to the 4-amino group of Boc-Pra-OCH3 and saponifying the methyl ester group.The iron(II)-braced tripod was assembled by S-alkylation of three copies of the leg peptide with 1,3,5-tris(bromomethyl)benzene followed by ligation of Fe2+ to the resulting unbraced tripod. The CD spectrum of the iron(II)-braced tripod showed a positive MLCT band at 570 nm and a negative –* band at 312 nm, so its FeII(Mbc)3 brace was predominantly in the configuration. In a mostly acetonitrile solution at 25 °C, the leg peptide and the unbraced tripod isomerized from the proline-II helical form into the proline-I helical form but the iron(II)-braced tripod remained in the proline-II helical form. 相似文献
2.
G. Park F. H. Lu N. Ye M. W. Brechbiel S. V. Torti F. M. Torti R. P. Planalp 《Journal of biological inorganic chemistry》1998,3(5):449-457
The interaction of Fe(II) and Fe(III) with the novel Fe(II) chelator N,N′N″-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane (referred to as tachpyr) gives rise to six-coordinate, low-spin, cationic complexes of Fe(II).
Tachpyr also displays a cytotoxicity toward cultured bladder cancer cells that is believed to involve coordination of intracellular
iron. The anaerobic reaction of tachpyr with Fe(II) salts affords the Fe(II)-tachpyr2+ complex, but in presence of oxygen, oxidative dehydrogenation of one or two of the aminomethylene group(s) of the ligand
occurs, with formal loss of H2: R—N(H)—C(H)2—(2-py) → R—N=C(H)—(2-py)+H2. The resulting mono- and diimino Fe(II) complexes (denoted as [Fe(tachpyr-H2)]2+ and [Fe(tachpyr-2H2)]2+) are an inseparable mixture, but they may be fully oxidized by H2O2 to the known tris(imino) complex Fe(II)[cis,cis-1,3,5-tris(pyridine-2-carboxaldimino)cyclohexane]2+ (or [Fe(tachpyr-3H2)]2+). Cyclic voltammetry of the imino complex mixture reveals an irreversible anodic wave at +0.78 V vs. NHE. Tachpyr acts as
a reducing agent toward Fe(IIII) salts, affording the same two Fe(II) imino complexes as products. Tachpyr also reductively
removes Fe(III) from an Fe(III)(ATP)3 complex (which is a putative form of intracellular iron), producing the two Fe(II) imino complexes. Novel N-alkylated derivatives of tachpyr have been synthesized. N-Alkylation has two effects on tachpyr: lowering metal affinity through increased steric hindrance, and preventing Fe(III)
reduction because oxidative dehydrogenation of nitrogen is blocked. The N-methyl tachpyr derivative binds Fe(II) only weakly as a high-spin complex, and no complexation or reduction of Fe(III) is
observed. Corresponding to their inability to bind iron, the N-alkylated chelators are nontoxic to cultured bladder cancer cells. A tach-based chelator with three N-propyleneamino arms is also synthesized. Studies of the chemical and biochemical properties of this chelator further support
a relationship between intracellular iron chelation, iron reduction, and cytotoxicity.
Received: 23 March 1998 / Accepted: 1 June 1998 相似文献
3.
Slate Cheryl A. Binstead Robert A. Meyer Thomas J. Erickson Bruce W. 《International journal of peptide research and therapeutics》1999,6(1):61-69
Summary The kinetics of isomerization of the helical forms of three oligoprolines was determined by far-ultraviolet CD spectropolarimetry
and kinetic analysis by singular value decomposition. ZRA (Pro3-X-Pro2-Y-Pro2-Z-Pro3) and ZRA2 (Pro7-X-Pro2-Y-Pro2-Z-Pro7) bear large redox-active substituents on proline residues X, Y, and Z, but P9 (Pro9) does not. All three peptides formed a stable proline-II helix in water. In acetonitrile, both ZRA2 and P9 were converted
into a proline-I helical form but ZRA remained predominantly in the proline-II helical form. Evidently, in order to undergo
substantial proline II→I isomerization, an oligoproline chain containing large substituents needs to have a segment of consecutive
unsubstituted proline residues that is sufficiently long to form a stable proline helix. Biexponential kinetics (A→B, k1=∼3.3×10−4s−1; B→C, k2=∼0.8×10−4s−1) were observed for the proline II→I isomerization of ZRA2 and P9 in acetonitrile and for the proline I→II isomerization of
ZRA2 in water, which provides evidence for the growth and decay of a major kinetic intermediate. 相似文献
4.
Suzanne Ferrere 《Inorganica chimica acta》2002,329(1):79-92
Ultrafast electron transfer in the dye sensitized solar cell (DSSC) has made it possible to use iron(II) polypyridyl complexes as photosensitizers [J. Am. Chem. Soc. 120 (1998) 843]. Although ruthenium(II) polypyridyl complexes comprise an extensively studied and widely utilized photochemical system, comparatively little is known about the photoproperties of their iron analogues. The syntheses and solution properties of the complexes [FeII(L)2(CN)2] and [FeIIL3] for a series of L, where L is a 2,2′-bipyridine derivative, are presented here. We compare the solvatochromism of [FeII(4,4′-dicarboxylic acid-2,2′-bipyridine)2(CN)2] to [FeII(4,4′-dimethyl-2,2′-bipyridine)2(CN)2] and discuss general trends in the electrochemistry and absorption properties within the series. The solvatochromism of these complexes is discussed in terms of their use in a dye sensitized TiO2 solar cell. 相似文献
5.
Wen-Je Lu Hui-Min Wang Jeu-Ming P. Yuann Ming-Hon Hou 《Journal of inorganic biochemistry》2009,103(12):1626-1633
Chromomycin (Chro) forms a 2:1 drug/metal complex through the chelation with Fe(II), Co(II), or Cu(II) ion. The effects of spermine on the interaction of Fe(II), Co(II), and Cu(II) complexes of dimeric Chro with DNA were studied. Circular dichroism (CD) measurements revealed that spermine strongly competed for the Fe(II) and Cu(II) cations in dimeric Chro-DNA complexes, and disrupted the structures of these complexes. However, the DNA-CoII(Chro)2 complex showed extreme resistance to spermine-mediated competition for the Co(II) cation. According to surface plasmon resonance (SPR) experiments, a 6 mM concentration of spermine completely abolished the DNA-binding activity of FeII(Chro)2 and CuII(Chro)2 and interfered with the associative binding of CoII(Chro)2 complexes to DNA duplexes, but only slightly affected dissociation. In DNA integrity assays, lower concentrations of spermine (1 and 2 mM) promoted DNA strand cleavage by CuII(Chro)2, whereas various concentrations of spermine protected plasmid DNA from damage caused by either CoII(Chro)2 or FeII(Chro)2. Additionally, DNA condensation was observed in the reactions of DNA, spermine, and FeII(Chro)2. Despite the fact that CuII(Chro)2 and FeII(Chro)2 demonstrated lower DNA-binding activity than CoII(Chro)2 in the absence of spermine, while CuII(Chro)2 and FeII(Chro)2 exhibited greater cytoxicity against HepG2 cells than CoII(Chro)2, possibly due to competition of spermine for Fe(II) or Cu(II) in the dimeric Chro complex in the nucleus of the cancer cells. Our results should have significant relevance to future developments in metalloantibiotics for cancer therapy. 相似文献
6.
Magnetite as a precursor for green rust through the hydrogenotrophic activity of the iron‐reducing bacteria Shewanella putrefaciens
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Magnetite (FeIIFeIII2O4) is often considered as a stable end product of the bioreduction of FeIII minerals (e.g., ferrihydrite, lepidocrocite, hematite) or of the biological oxidation of FeII compounds (e.g., siderite), with green rust (GR) as a mixed FeII‐FeIII hydroxide intermediate. Until now, the biotic transformation of magnetite to GR has not been evidenced. In this study, we investigated the capability of an iron‐reducing bacterium, Shewanella putrefaciens, to reduce magnetite at circumneutral pH in the presence of dihydrogen as sole inorganic electron donor. During incubation, GR and/or siderite (FeIICO3) formation occurred as secondary iron minerals, resulting from the precipitation of FeII species produced via the bacterial reduction of FeIII species present in magnetite. Taking into account the exact nature of the secondary iron minerals and the electron donor source is necessary to understand the exergonic character of the biotic transformation of magnetite to GR, which had been considered to date as thermodynamically unfavorable at circumneutral pH. This finding reinforces the hypothesis that GR would be the cornerstone of the microbial transformations of iron‐bearing minerals in the anoxic biogeochemical cycle of iron and opens up new possibilities for the interpretation of the evolution of Earth's history and for the understanding of biocorrosion processes in the field of applied science. 相似文献
7.
Udai P. Singh Raj K. Singh Yashuhiro Isogai Yoshitsugu Shiro 《International journal of peptide research and therapeutics》2006,12(4):379-385
The de novo peptide with 63-residues (MHB) has been synthesized biochemically and used for the binding of manganese (II) ions. In designed peptide, the leucine of the peptide dA1 (prototype) was replaced by His27 and Asp41 for binding the manganese (II) ions. The different chromatography studies and mass determination showed that new peptide folds into a monomeric, highly helical with a active site structure similar to the native Mn–SOD in an aqueous solution. Electron paramagnetic resonance (EPR) study suggested that the peptide binds single manganese (II) ion per molecule loosely with K
D value of about 36 μM. The circular dichroism (CD) studies demonstrated that the helical contents of the peptide did not change significantly even after binding the metal ions. The SOD activity study of the Mn–peptide complex showed that the IC50 values is 8.08 μM. 相似文献
8.
Summary Copper(II) complexes CuL1L2 with the ligand pairs 3-phosphoglycerate (PG)/ethylenediamine (en), phosphoserine (PS)/ethylenediamine, phosphoserine/malonate (mal) are shown to be effective in inducing the release of both iron atoms from di-ferric transferrin (Fe2Tf; human serum transferrin) at pH 7.3 in 1 M NaCl at 25°C. Half-times of the reaction with Cu(PG)(en)– were less than 1 min at 0.02 M concentration. The iron(III) products are polynuclear hydroxo complexes. There is weaker interaction with Cu(PS)
2
4–
and virtually none with Cu(serine)(en) nor Cu(PS)(2,2-bipyridyl)–, revealing crucial effects of the combined ligand sphere including the phosphomonoester group. The results suggest that the release of iron from Fe2Tf, or from either monoferric transferrins, occurred due to the breakdown of the stability of iron binding in conjunction with the expulsion of the synergistic anion carbonate (or oxalate). The active copper(II) complexes are postulated to be models of membrane components that could liberate iron from transferrin succeeding its uptake at the receptor sites of cells.Abbreviations PG
phosphoglycerate
- PS
phosphoserine
- en
ethylenediamine
- Fe2Tf
diferric transferrin
- FecTf and FeNTf
transferrin with iron bound to the lobe containing the C- or N-terminus, respectively
- apoTf
apotransferrin
- K-3
all-cis-1,3,5-tris(trimethylammonio)-2,4,6-cyclo-hexanetriol
- NTA
nitrilotriacetic acid; bipy, 2,2-bipyridine; mal, malonate 相似文献
9.
Distinct chemical species of iron were investigated by Mössbauer spectroscopy during iron uptake into cucumber roots grown in unbuffered nutrient solution with or without 57Fe-citrate. Mössbauer spectra of iron deficient roots supplied with 10–500 μM 57Fe-citrate for 30–180 min and 24 h and iron-sufficient ones, were recorded. The roots were analysed for Fe concentration and Fe reductase activity. The Mössbauer parameters in the case of iron-sufficient roots revealed high-spin iron(III) components suggesting the presence of FeIII-carboxylate complexes, hydrous ferric oxides and sulfate–hydroxide containing species. No FeII was detected in these roots. However, iron-deficient roots supplied with 0.5 mM 57FeIII-citrate for 30 min contained significant amount of FeII in a hexaaqua complex form. This is a direct evidence for the Strategy I iron uptake mechanism. Correlation was found between the decrease in Fe reductase activity and the ratio of FeII–FeIII components as the time of iron supply was increased. The data may refer to a higher iron reduction rate as compared to its uptake/reoxidation in the cytoplasm in accordance with the increased reduction rate in iron deficient Strategy I plants. 相似文献
10.
Leiter E Emri T Gyémánt G Nagy I Pócsi I Winkelmann G Pócsi I 《Folia microbiologica》2001,46(2):127-132
Late-exponential-phasePenicillium chrysogenum mycelia grown in a complex medium possessed an intracellular iron concentration of 650 μmol/L (2.2±0.6 μmol per g mycelial
dry mass). This iron reserve was sufficient to ensure growth and antibiotic production after transferring mycelia into a defined
low-iron minimal medium. Although the addition of Fe3+ to the Fe-limited cultures increased significantly the intracellular iron levels the surplus iron did not influence the production
of penicillin V. Supplements of purified majorP. chrysogenum siderophores (coprogen and ferrichrome) into the fermentation media did not affect the β-lactam production and intracellular
iron level. Neither 150 nor 300 μmol/L extracellular Fe3+ concentrations disturbed the glutathione metabolism of the fungus, and increased the oxidative stress caused by 700 mmol/L
H2O2. Nevertheless, when iron was applied in the FeII oxidation state the oxidative cell injuries caused by the peroxide were significantly enhanced. 相似文献
11.
Achim Sokolowski Heiko Leutbecher Thomas Weyhermüller Robert Schnepf Eberhard Bothe Eckhard Bill Peter Hildebrandt K. Wieghardt 《Journal of biological inorganic chemistry》1997,2(4):444-453
The reaction of the macrocycles 1,4,7-tris (3,5-di-tert-butyl-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L1H3, or 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L2H3, with Cu(ClO4)2·6H2O in methanol (in the presence of Et3N) affords the green complexes [CuII(L1H)] (1), [CuII(L2H)]·CH3OH (2) and (in the presence of HClO4) [CuII(L1H2)](ClO4) (3) and [CuII(L2H2)] (ClO4) (4). The CuII ions in these complexes are five-coordinate (square-base pyramidal), and each contains a dangling, uncoordinated pendent
arm (phenol). Complexes 1 and 2 contain two equatorially coordinated phenolato ligands, whereas in 3 and 4 one of these is protonated, affording a coordinated phenol. Electrochemically, these complexes can be oxidized by one electron,
generating the phenoxyl-copper(II) species [CuII(L1H)]+ ·, [Cu(L2H)]+ ·, [CuII(L1H2)]2+ ·, and [CuII(L2H2)]2+ ·, all of which are EPR-silent. These species are excellent models for the active form of the enzyme galactose oxidase (GO).
Their spectroscopic features (UV-VIS, resonance Raman) are very similar to those reported for GO and unambiguously show that
the complexes are phenoxyl-copper(II) rather than phenolato-copper(III) species.
Received: 10 February 1997 / Accepted: 7 April 1997 相似文献
12.
Previous studies have demonstrated that 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone (NIH) and several other aroylhydrazone
chelators possess anti-neoplastic activity due to their ability to bind intracellular iron. In this study we have examined
the structure and properties of NIH and its FeIII complex in order to obtain further insight into its anti-tumour activity. Two tridentate NIH ligands deprotonate upon coordination
to FeIII in a meridional fashion to form a distorted octahedral, high-spin complex. Solution electrochemistry of [Fe(NIH–H)2]+ shows that the trivalent oxidation state is dominant over a wide potential range and that the FeII analogue is not a stable form of this complex. The fact that [Fe(NIH–H)2]+ cannot cycle between the FeII and FeIII states suggests that the production of toxic free-radical species, e.g. OH
.
or O2
.
–, is not part of this ligand's cytotoxic action. This suggestion is supported by cell culture experiments demonstrating that
the addition of FeIII to NIH prevents its anti-proliferative effect. The chemistry of this chelator and its FeIII complex are discussed in the context of understanding its anti-tumour activity.
Received: 12 November 1998 / Accepted: 9 February 1999 相似文献
13.
Transferrin (Tf) is a kind of non-heme β-globulin with two iron ions (Fe3+)-binding sites. To prove Tf’s physiological functions, Fe3+-proteins, serum iron contents, and total iron-binding capabilities were tested for Tfs of crucian carps (Carassius auratus) and sliver carps (Hypophthalmichthys molitrix). The above results demonstrated that sliver carps shared 1/3 Tf alleles with crucian carps; Tf of crucian carps had stronger
Fe3+-binding ability and transportation ability in plasma than that of sliver carps. In addition, the results of oxygen consumption
experiments indicated that crucian carps had the higher oxygen utility rate than sliver carps. For acute hypoxia exposure
assay, normoxic gas mixture, hypoxic gas mixture A, and hypoxic gas mixture B were used to induce oxygen-regulated gene expression
of crucian carps in acute hypoxia. The results of quantitative real-time PCR revealed that mRNA levels of Tf gene, Tfr gene
and ATPase gene were down-regulated in acute hypoxia but mRNA level of LDHa gene was up-regulated in acute hypoxia. The results
of crucian carp Tf-cDNA sequence analysis showed that cDNA regions of two Fe3+-binding sites were T747–T1026 and T1737–A1884 based on the principle of bioinformatics. The sequence conservation of two Fe3+-binding sites was higher than that of the other five regions, which were confirmed according to the subregion model of Tf-cDNA
sequence. 相似文献
14.
15.
Xavier FR Peralta RA Bortoluzzi AJ Drago V Castellano EE Haase W Tomkowicz Z Neves A 《Journal of inorganic biochemistry》2011,105(12):1740-1752
In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [FeIIICdII(L)(μ-OAc)2]ClO4·0.5H2O (1) complex containing the unsymmetrical ligand H2L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe2IIIHg2II(L)2(OH)2](ClO4)2·2CH3OH (2) and [FeIIIHgII(L)(μ-CO3)FeIIIHgII(L)](ClO4)2·H2O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [FeIII2HgII2(L)2(OH)2](ClO4)2·2CH3OH (2) can be converted to (3) by the fixation of atmospheric CO2 since the crystal structure of the tetranuclear organometallic complex [FeIIIHgII(L)(μ-CO3)FeIIIHgII(L)](ClO4)2·H2O (3) with an unprecedented {FeIII(μ-Ophenoxo)2(μ-CO3)FeIII} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a FeIII-bound hydroxo group on the CO2 molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the FeIII centers in 3 are antiferromagnetically coupled (J = − 7.2 cm− 1) and that the FeIII-OR-FeIII angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with kH/kD isotope effects, the kinetic studies suggest a mechanism in which a terminal FeIII-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long FeIII…HgII distance could be responsible for the lower catalytic effectiveness of 2. 相似文献
16.
An oxalate-bridged binuclear iron(III) complex, [(acac)2Fe(μ-ox)Fe(acac)2], (acac−=acetylacetonate anion and ox2−=oxalate anion) was prepared. The complex crystallized as two types of crystals under different conditions: one had 1,2-dichloroethane as a solvent molecule of crystallization 2, the other did not 1. Both compounds have been characterized by X-ray crystallography, infrared spectroscopy, and thermogravimetric analysis. Compound 1 has also been characterized by UV-Vis and 1H NMR spectroscopies, mass spectrometry, and electrochemistry. In both crystals, each iron(III) is coordinated in an octahedral arrangement by the oxygen atoms of an oxalate-bridging ligand and four oxygen atoms belonging to peripheral acac ligands in an octahedral arrangement. The intermetallic distance of Fe?Fe is 5.4368(9) Å in 1 and 5.438(2) Å in 2. Two iron(III) ions in each crystal are bridged by the oxalate and both lie in the oxalate-plane. The results of thermal analyses imply that the thermal stability of 2 is lower than that of 1. Cyclic voltammograms of 1 in acetonitrile and dichloromethane at low temperature showed two consecutive, quasi-Nernstian, one-electron reduction steps corresponding to the reduction of FeIII-FeIII to FeIII-FeII followed by the reduction of FeIII-FeII to FeII-FeII. The electrochemical comproportionation constants (Kc) of the equilibrium (FeIII-FeIII) + (FeII-FeII) ? 2(FeIII-FeII) are 108.9 in acetonitrile medium and 108.5 in dichloromethane, respectively. The considerably large Kc values indicate that the main factor contributing to the stabilization of the FeIII-FeII mixed-valence state is electronic delocalization through the oxalate-bridge. 相似文献
17.
The thermostabilities of Fe2+ ligation in rubredoxins (Rds) from the hyperthermophile Pyrococcus furiosus (Pf) and the mesophiles Clostridium pasteurianum (Cp) and Desulfovibrio vulgaris (Dv) were compared. Residue 44 forms an NH...S(Cys) hydrogen bond to one of the cysteine ligands to the [Fe(SCys)4] site, and substitutions at this location affect the redox properties of the [Fe(SCys)4] site. Both Pf Rd and Dv Rd have an alanine residue at position 44, whereas Cp Fd has a valine residue. Wild-type proteins were examined along with V44A and A44V exchange mutants of Cp and Pf Rds, respectively, in order to assess the effects of the residue at position 44 on the stability of the [Fe(SCys)4] site. Stability of iron ligation was measured by temperature-ramp and fixed-temperature time course experiments, monitoring iron release in both the absence and presence of more thiophilic metals (Zn2+, Cd2+) and over a range of pH values. The thermostability of the polypeptide fold was concomitantly measured by fluorescence, circular dichroism, and 1H NMR spectroscopies. The A44V mutation strongly lowered the stability of the [FeII(SCys)4] site in Pf Rd, whereas the converse V44A mutation of Cp Rd significantly raised the stability of the [FeII(SCys)4] site, but not to the levels measured for wild-type Dv Rd. The region around residue 44 is thus a significant contributor to stability of iron coordination in reduced Rds. This region, however, made only a minor contribution to the thermostability of the protein folding, which was found to be higher for hyperthermophilic versus mesophilic Rds, and largely independent of the residue at position 44. These results, together with our previous studies, show that localized charge density, solvent accessibility, and iron site/backbone interactions control the thermostability of the [Fe(SCys)4] site. The iron site thermostability does make a minor contribution to the overall Rd thermostability. From a mechanistic standpoint, we also found that attack of displacing ions (H+, Cd2+) on the Cys42 sulfur ligand at the [Fe(SCys)4] site occurs through the V8 side and not the V44 side of the iron site.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00775-004-0525-4Abbreviations BPS bathophenanthroline sulfonate, sodium salt - Cp Rd (Pf Rd, Dv Rd) recombinant rubredoxin from Clostridium pasteurianum (Pyrococcus furiosus, Desulfovibrio vulgaris) - HEPES hydroxyethylpiperazineethanesulfonic acid - MES morpholinoethanesulfonic acid - Tris tris(hydroxymethyl)aminomethane - wt wild-type - ZnRd recombinant rubredoxin containing a [Zn(SCys)4] site 相似文献
18.
Joo-Yeon Han Astrid Gräslund Lars Thelander A. G. Sykes 《Journal of biological inorganic chemistry》1997,2(3):287-294
Four reductions of the R2 subunit of mouse ribonucleotide reductase have been studied and found to exhibit different behaviour
from that of Escherichia coli R2. An important difference is that there is no stable met-R2 (Fe2
II I) form of mouse R2. With hydroxyurea, hydrazine and hydroxylamine uniphasic kinetics are observed for the combined reduction
of radical Tyr ˙ and Fe2
II I components to tyrosine and Fe2
II respectively. The rate constants, determined at 370 nm (emphasising FeIII decay) and 417 nm (emphasising Tyr ˙ decay), differ by factors of 2–3, allowing some mechanistic features to be defined. The studies with hydrazine are particularly
important. In the case of E. coli R2, a first phase corresponding to two-equivalent reduction of the met-R2 component has been observed [18]. It is likely
that the four times slower second phase reaction of active E. coli R2 also corresponds to the Fe2
II I → Fe2
II change and is followed by fast intramolecular Fe2
II reduction of the higher potential Tyr ˙. The latter changes are believed to hold also for (active) mouse R2. The FeIIFeIII semi forms have been detected at low levels by EPR for mouse R2 (9%) and E. coli (∼5%) in previous studies. Further substrate reduction of FeIIFeIII occurs at a comparable rate to account for the transient behaviour of FeIIFeIII. For mouse R2 the combined FeIII decay processes (which we are unable to separate) give smaller uniphasic rate constants at 370 nm than at 417 nm. A fitted-base-line
(FBL) treatment of absorbance changes at 417 nm targets more closely the Tyr ˙ decay as a means of monitoring the rate-determining step. The FBL method gives rate constants k (M–1 s–1) at 25 °C and pH 7.5 for hydroxyurea (1.46), hydrazine (0.163) and hydroxylamine (4.4). Surprisingly, phenylhydrazine, with
a less strong reduction potential (0.25 V), gives a substantially faster reduction of the Tyr ˙ as the only redox step (rate constant 27 M–1 s–1). In this case a slower second phase at 370 nm is independent of reductant and corresponds to rate-controlling release of
FeIII. Overall the results indicate a more reactive redox centre for mouse R2 and help develop further an understanding of factors
affecting the reactivity of R2.
Received: 11 October 1996 / Accepted: 11 February 1997 相似文献
19.
Sano Y Onoda A Sakurai R Kitagishi H Hayashi T 《Journal of inorganic biochemistry》2011,105(5):702-708
Metallothioneins (MTs) are small cysteine-rich proteins which exhibit high affinities for various metal ions and play roles in storage of essential metals and detoxification of toxic metals. Studies on the redox properties of MTs have been quite limited. Recently, we focused on the α-domain of MT (MTα) as a protein matrix and incorporated a tetranuclear metal cluster as a reductant. UV-visible, CD and MS data indicate the formation of the stable tetranuclear metal-cysteine cluster in the MTα matrix with FeII4-MTα and CoII4-MTα species existing in water. Furthermore, the FeII4-MTα species was found to promote the reduction of met-myoglobin and azobenzene derivatives under mild conditions. Particularly, the stoichiometric reduction of methyl red with FeII4-MTα (1:1) was found to proceed with a conversion of 98% over a period of 6 h at 25 °C. This indicates that all of the four Fe(II) cores contribute to the reduction. In this paper, we describe the preparation and reactivity of the tetranuclear iron cluster in the protein matrix. 相似文献
20.
Eyal Zobel Eylon Yavin Hugo E. Gottlieb Meirav Segal Bilha Fischer 《Journal of biological inorganic chemistry》2010,15(4):601-620
We report on a rather unknown feature of oligonucleotides, namely, their potent antioxidant activity. Previously, we showed
that nucleotides are potent antioxidants in FeII/CuI/II–H2O2 systems. Here, we explored the potential of 2′-deoxyoligonucleotides as inhibitors of the FeII/CuI/II-induced ·OH formation from H2O2. The oligonucleotides [d(A)5,7,20; d(T)20; (2′-OMe-A)5] proved to be highly potent antioxidants with IC50 values of 5–17 or 48–85 μM in inhibiting FeII/CuI- or CuII-induced H2O2 decomposition, respectively, thus representing a 40–215-fold increase in potency as compared with Trolox, a standard antioxidant.
The antioxidant activity is only weakly dependent on the oligonucleotides’ length or base identity. We analyzed by matrix-assisted
laser desorption/ionization time of flight mass spectrometry and 1H-NMR spectroscopy the composition of the d(A)5 solution exposed to the aforementioned oxidative conditions for 4 min or 24 h. We concluded that the primary (rapid) inhibition
mechanism by oligonucleotides is metal ion chelation and the secondary (slow) mechanism is radical scavenging. We characterized
the CuI–d(A)5 and CuII–d(A)7 complexes by 1H-NMR and 31P-NMR or frozen-solution ESR spectroscopy, respectively. CuI is probably coordinated to d(A)5 via N1 and N7 of two adenine residues and possibly also via two phosphate/bridging water molecules. The ESR data suggest
CuII chelation through two nitrogen atoms of the adenine bases and two oxygen atoms (phosphates or water molecules). We conclude
that oligonucleotides at micromolar concentrations prevent FeII/CuI/II-induced oxidative damage, primarily through metal ion chelation. Furthermore, we propose the use of a short, metabolically
stable oligonucleotide, (2′-OMe-A)5, as a highly potent and relatively long lived (t
1/2 ~ 20 h) antioxidant. 相似文献