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Query: UNIPROT:O14944 (EPR)
 13,097 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The anion-binding properties of lactoferrin (Lf), with Fe3+ or Cu2+ as the associated metal ion, have been investigated by physicochemical and crystallographic techniques. These highlight differences between the two sites and in the anion-binding behavior when different metals are bound. Carbonate, oxalate, and hybrid carbonate-oxalate complexes have been prepared and their characteristic electronic and EPR spectra recorded. Oxalate can displace carbonate from either one or both anion sites of Cu2(CO3)2Lf, depending on the oxalate concentration, but no such displacement occurs for Fe2(CO3)2Lf. Addition of oxalate and the appropriate metal ion to apoLf under carbonate-free conditions gives dioxalate complexes with both Fe3+ and Cu2+, except when traces of EDTA remain associated with the protein, when hybrid complexes M2(CO3)(C2O4)Lf can result. The anion sites in the crystal structures of Fe2(CO3)2Lf, Cu2-(CO3)2Lf, and Cu2(CO3)(C2O4)Lf, refined at 2.2, 2.1, and 2.2 A, respectively, have been compared. In every case, the anion is hydrogen bonded to the N-terminus of helix 5, an associated arginine side chain, and a nearby threonine side chain. The carbonate ion binds in bidentate fashion to the metal, except in the N-lobe site of dicupric lactoferrin, where it is monodentate; the difference arises from slight movement of the metal ion. The hybrid complex shows that the oxalate ion binds preferentially in the C-lobe site, in 1,2-bidentate mode, but with the displacement of several nearby side chains. These observations lead to a generalized model for synergistic anion binding by transferrins.
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PMID:Anion binding by human lactoferrin: results from crystallographic and physicochemical studies. 158 1

We have examined the kinetics and mechanism by which iron can displace copper at the specific metal-binding sites of ovotransferrin. Fe2+ was added to Cu2+-ovotransferrin-CO3(2-) in the presence of NaHCO3 and ambient O2. The reaction has been followed by standard and stopped-flow spectrophotometry, EPR spectroscopy and analysis of chromogen-reactive Fe2+. The reaction is best described as triphasic. An initial jump in absorbance takes place in the first 2 s. In the next minute there is a further increase in absorbance and shift in the spectral maximum from 440 to 446 nm. The third phase is complex. The bulk of the spectrophotometric change, a decrease in absorbance with a shift to a maximum of 453 nm, lasts approx. 3 min. Minor spectral and EPR changes, however, take place over the next several hours. Chromogenic analysis of Fe2+ indicates that approx. 1 min is required to oxidize the Fe2+. EPR spectra reveal the formation of an Fe3+-ovotransferrin complex within the first 20 s; however, this lacks the characteristic doublet of specific Fe3+-ovotransferrin-CO3(2-). The simultaneous presence of specific Cu2+-ovotransferrin-CO3(2-) and Fe3+-ovotransferrin-CO3(2-) signals suggests a period in which the protein specifically binds both metal ions perhaps resulting from a differential reactivity of the two metal-binding sites. The addition of Cu(NO3)2 to Fe3+-ovotransferrin-CO3(2-) resulted in a complex with specific Fe3+ and non-specific Cu2+. The EPR spectrum of this complex and the final product of our displacement reaction were virtually identical. Distinct parallels in reaction of Cu2+-ovotransferrin-CO3(2-) with Fe(NH4)2(SO4)2, Fe(NO3)3 and Fe3+-nitrilotriacetic acid were observed. A reaction sequence involving the binding and oxidation of non-specific Fe2+ followed by Cu2+ displacement by Fe3+ at the specific sites and binding of non-specific Cu2+ is suggested.
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PMID:The displacement of copper by iron at the specific binding sites of ovotransferrin. 254 50

An EPR study of human tooth enamel dried at 400 degrees C is presented. Enamel blocks as well as powdered samples were investigated. The discussion deals mainly with three different spectral components, i.e., a CO3(3-) and two different CO2- signals. Using the anisotropic enamel block spectra, a convincing differentiation between the latter two radicals was possible. The first CO2- signal shows no dependence on the orientation of the enamel blocks, disappears from the spectrum upon heating, and was assigned to a surface radical. The second CO2- component is mainly responsible for the angular variation of the enamel blocks and is assigned to a bulk position. For the CO3(3-) ion, the (pseudo) angular variation of its isolated spectrum is presented and discussed. By means of the results presented in this study, earlier interpretation problems are considerably reduced.
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PMID:An EPR study of intact and powdered human tooth enamel dried at 400 degrees C. 764 84

The anion binding properties of human lactoferrin (Lf), with Fe3+ or Cu2+ as the associated metal ion, highlight differences between the two sites, and in the anion binding behaviour when different metals are bound. Carbonate, oxalate and hybrid carbonate-oxalate complexes have been prepared and their characteristic electronic and EPR spectra recorded. Oxalate can displace carbonate from either one or both anion sites of Cu2(CO3)2Lf, depending on the oxalate concentration, but no such displacement occurs for Fe2(CO3)2Lf although it does for the bovine analogue. Addition of oxalate and the appropriate metal ion to apoLf under carbonate-free conditions gives dioxalate complexes with both Fe3+ and Cu2+. The anion sites as determined from the crystal structures of Fe2(CO3)2Lf, Fe2(C2O4)2Lf, Cu2(CO3)2Lf, and Cu2(CO3)(C2O4)Lf have been compared. Both the carbonate and oxalate ions bind in bidentate fashion to the metal, except that the carbonate ion in the N-lobe site of dicupric lactoferrin is monodentate. The hybrid copper lactoferrin complex shows that the oxalate ion binds preferentially in the C-lobe site in a bidentate mode. A series of complexes containing the synergistic anion O,N-chelates with increasing substitution on the N atom (glycinate, iminodiacetate and nitrilotriacetate) have been prepared with iron bovine lactoferrin for comparison with the O,O-chelate oxalate. Overall these observations lead to a generalised model for synergistic anion binding by transferrins and allow comparisons to be made with nonsynergistic anions such as citrate and succinate.
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PMID:Synergism and substitution in the lactoferrins. 776 44

Rates of radiolytic inactivation of bacteria suspended in N2O-saturated solutions were dramatically increased over normal background levels when the media contained chloride or bicarbonate ions. The bacteria could be protected from this enhanced toxicity by the addition of free radical scavengers (ethanol, ascorbate, hydrogen peroxide, mannitol, glucose, EDTA, picolinic acid), indicating that the lethal reactions were extracellular in origin. Prior irradiation of chloride-containing solutions led to formation of hypochlorous acid, which was identified by detection of ring-chlorinated products when reacted with fluorescein. Prolonged irradiation of other solutions did not lead to accumulation of bactericidal agents; however, irradiation of bicarbonate-containing solutions in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) led to formation of the EPR-detectable DMPO.CO3- adduct. The results are interpreted in terms of formation of secondary radicals, among which the carbonate and chlorine radicals are uniquely toxic to bacteria. From rate comparisons of the solution components, it was concluded that the reactions involving chloride ion are unlikely to be expressed in biological environments, but that the CO3- radical could be an important intermediary oxidant in peroxide-inflicted cellular damage, particularly in spatially confined environments such as the leukocyte phagosome.
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PMID:Bactericidal potency of hydroxyl radical in physiological environments. 814 63

Synthetic A-type carbonated apatite samples were irradiated at room temperature with 60Co gamma rays. Their ESR spectra consist of the lines of CO2- and CO3- radicals of orthorhombic and axial symmetry. The measurements carried out immediately after sample irradiation showed that CO2- species are produced by decomposition of CO3- radicals. Intensity of the CO2- lines in the synthetic and enamel samples increases during the first 400 and 200 h after irradiation, respectively. The dependence of the EPR signal on the dose varies with carbonate content of the sample. The dose response curve for tooth enamel is steeper for the synthetic material.
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PMID:Gamma dose response of synthetic A-type carbonated apatite in comparison with the response of tooth enamel. 1083 11

In order to determine the components which give rise to the EPR spectrum around g = 2 we have applied Maximum Likelihood Common Factor Analysis (MLCFA) on the EPR spectra of enamel sample 1126 which has previously been analysed by continuous wave and pulsed EPR as well as EPR microscopy. MLCFA yielded agreeing results on three sets of X-band spectra and the following components were identified: an orthorhombic component attributed to CO2-, an axial component (CO3(3-)), as well as four isotropic components, three of which could be attributed to SO2-, a tumbling CO2- and a central line of a dimethyl radical. The X-band results were confirmed by analysis of Q-band spectra where three additional isotropic lines were found, however, these three components could not be attributed to known radicals. The orthorhombic component was used to establish dose response curves for the assessment of the past radiation dose, D(E). The results appear to be more reliable than those based on conventional peak-to-peak EPR intensity measurements or simple Gaussian deconvolution methods.
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PMID:EPR spectrum deconvolution and dose assessment of fossil tooth enamel using maximum likelihood common factor analysis. 1083 49

Mono- and dicopper(II) complexes of a series of potentially bridging hexaamine ligands have been prepared and characterized in the solid state by X-ray crystallography. The crystal structures of the following Cu(II) complexes are reported: [Cu(HL3)](ClO4)(3), C11H31Cl3CuN6O12, monoclinic, P2(1)/n, a = 8.294(2) A, b = 18.364(3) A, c = 15.674(3) A, beta = 94.73(2) degrees, Z = 4; ([Cu2(L4)(CO3)](2))(ClO4)(4).4H2O, C40H100Cl4Cu4N12O26, triclinic, P1, a = 9.4888(8) A, b = 13.353(1) A, c = 15.329(1) A, alpha = 111.250(7) degrees, beta = 90.068(8) degrees, gamma = 105.081(8) degrees, Z = 1; [Cu2(L5)(OH2)(2)](ClO4)(4), C13H36Cl4Cu2N6O18, monoclinic, P2(1)/c, a = 7.225(2) A, b = 8.5555(5) A, c = 23.134(8) A, beta = 92.37(1) degrees, Z = 2; [Cu2(L6)(OH2)(2)](ClO4)(4).3H2O, C14H44Cl4Cu2N6O21, monoclinic, P2(1)/a, a = 15.204(5) A, b = 7.6810(7) A, c = 29.370(1) A, beta = 100.42(2) degrees, Z = 4. Solution spectroscopic properties of the bimetallic complexes indicate that significant conformational changes occur upon dissolution, and this has been probed with EPR spectroscopy and molecular mechanics calculations.
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PMID:Diverse solid-state and solution structures within a series of hexaamine dicopper(II) complexes. 1130 Aug 3

The oxidant peroxynitrite/peroxynitrous acid (ONOO-/ONOOH) is generated at sites of inflammation via reaction of O2.- with .NO. Previous studies have shown that these species can oxidize cellular targets, but few data are available on damage to extracellular matrix and its components, despite evidence for matrix modification in a number of pathologies. In the current study we show that reaction of ONOO-/ONOOH with glycosaminoglycans results in extensive polymer fragmentation. Bolus authentic ONOO-/ONOOH modifies hyaluronan, heparin, and chondroitin, dermatan, and heparan sulfates, in a concentration-dependent, but O2-independent, manner. The ONOO-/ONOOH generator 3-(4-morpholinyl)sydnoneimine produces similar time- and concentration-dependent damage. These reactions generate specific polymer fragments via cleavage at disaccharide intervals. Studies at different pH values, and in the presence of bicarbonate, are consistent with ONOOH, rather than the carbonate adduct, CO3.- or ONOO-, being the source of damage. EPR spin trapping experiments have provided evidence for the formation of carbon-centered radicals on glycosaminoglycans and related monosaccharides; the similarity of these spectra to those obtained with authentic HO. is consistent with fragmentation being induced by this oxidant. These data suggest that extracellular matrix fragmentation at sites of inflammation may be due, in part, to the formation and reactions of ONOOH.
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PMID:Degradation of matrix glycosaminoglycans by peroxynitrite/peroxynitrous acid: evidence for a hydroxyl-radical-like mechanism. 1738 8

Glycosaminoglycans (long-chain polysaccharides) are major components of the extracellular matrix, glycocalyx, and synovial fluid. These materials provide strength and elasticity to tissues and play a key role in regulating cell behavior. Modifications to these materials have been linked to multiple human pathologies. Although modification may occur via both enzymatic and nonenzymatic mechanisms, there is considerable evidence for oxidant-mediated matrix damage. Peroxynitrite (ONOO(-)/ONOOH) is a potential mediator of such damage, as elevated levels of this oxidant are likely to be present at sites of inflammation. In this study we demonstrate that hyaluronan and chondroitin sulfate are extensively depolymerized by HO(.) and CO3(.-), but not NO2(.), which may be formed from peroxynitrite. Polymer fragmentation is shown to be dependent on the radical flux, to be O2-independent, and to occur in a site-selective manner as indicated by the detection of disaccharide fragments. EPR spin trapping experiments with polymers, oligomers, and component monosaccharides, including 13C-labeled materials, have provided evidence for the formation of specific carbon-centered sugar-derived radicals. The time course of formation of these radicals is consistent with these species being involved in polymer fragmentation.
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PMID:Glycosaminoglycans are fragmented by hydroxyl, carbonate, and nitrogen dioxide radicals in a site-selective manner: implications for peroxynitrite-mediated damage at sites of inflammation. 1942 78


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