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At least 109 records · Page 6Linked to original sources
PubMed1993

Activation of UICC crocidolite: the effect of conversion of some ferric ions to ferrous ions.

Asbestos fibers catalyze the generation of oxygen-centered radicals in the presence of oxygen or hydrogen peroxide. The amount of iron in asbestos fibers, its oxidation state, and its availability to specific chelating agents determine their ability to catalyze the aforementioned reactions. In the present study, the activation of UICC crocidolite was achieved by converting some of the ferric ions into ferrous ions. The activation process did not interfere with the size distribution, surface area, or crystal structure of these fibers. Although oxygen-centered radicals generated and lipid peroxidation produced by asbestos fibers are reported to play an important role in their toxicity, factors such as size, surface area, and durability are considered to be crucial determinants of fiber toxicity and carcinogenicity. The employment of the activated crocidolite in animal experiments to help further elucidate the importance of oxygen free radicals and lipid peroxidation in fiber-induced diseases is therefore proposed.

Asbestos↗
PubMed1995

Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materials.

Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mössbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mössbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mössbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.

Aluminum Silicates↗
PubMed1995

The mobile ferrous iron pool in Escherichia coli is bound to a phosphorylated sugar derivative.

Based on in vivo Mössbauer spectroscopy it has previously been demonstrated that the intracellular iron pool of Escherichia coli, grown in iron deficient media supplemented with siderophores as the sole iron source, is dominated by a single Fe2+ and a single Fe3+ species. We have isolated the ferrous ion species and have purified it employing native column PAGE, chromatography and ultrafiltration. The purified compound displays an Mapp of 2.2 kDa and an extremely low isoelectric point (pI) of 1.05. It is shown that this ferrous ion binding compound is neither a protein nor a nucleotide, rather it is composed mainly of phosphorylated sugar derivatives. This compound binds approximately 40% of the cytoplasmic iron. Therefore it is proposed that this oligomeric ferrous carbohydrate phosphate represents the long sought after mobile, low molecular mass iron pool.

Carbohydrate Metabolism↗
PubMed1996

The interaction of Fe(III), adriamycin and daunomycin with nucleotides and DNA and their effects on cell growth of fibroblasts (NIH-3T3).

The interactions of the iron complexes of the anthracycline antitumour drugs daunomycin (DN) and adriamycin (ADM) with the mononucleotide AMP, herring sperm DNA, plasmic pBR322 and immortalized 3T3 fibroblasts were studied. By means of Mössbauer spectroscopy it was demonstrated that DNA is a powerful ferric iron chelator as compared with AMP, which is not able to compete with DN or acetohydroxamic acid for ferric iron. The difference between AMP and DNA is postulated to be based on the chelate effect. The Mössbauer spectra of the ternary Fe-anthracycline-DNA systems differ from Fe-anthracycline binary complexes, indicating rearrangement reactions. Dialysis experiments clearly disclose the formation of a ternary Fe-ADM-pBR322 complex, the topology of which differs substantially from intercalating ADM. The effect of Fe-ADM complexes (3:1) on the growth of immortalized mouse embryonal fibroblasts (NIH-3T3) was studied in comparison with ADM alone. No significant difference on the inhibition of cell growth was noticed, suggesting comparable cytotoxicity for the compounds. In contrast to literature data, no evidence was found for DNA cleavage by ferric ADM at molar ratios as high as 1/100 (ADM/base pair), even if the ternary systems were prepared in the light and in the presence of reducing or oxidizing agents. Based on our observations it seems that the cytotoxicity of both ADM and Fe-ADM oligomer is not based primarily on intercalation or direct interaction with DNA.

3T3 Cells↗
PubMed1994

Mössbauer spectra of the heme peptide (HP) 1-50 and the heme peptide:non-heme peptide (NHP) non-covalent complex 1-50:51-104 derived from cytochrome c: evidence for cytochrome c iron site solvation in aqueous solution.

Mössbauer spectroscopic studies on a heme peptide (HP) derived from cytochrome c and on the HP recombined non-covalently with the remaining cleaved section are reported. The results suggest that the environment of the heme site in the known crystal structure of cytochrome c may differ in detail from the environment of the heme in the working protein.

Cytochrome c Group↗
PubMed1991

Hemoglobin dynamics in rat erythrocytes investigated by Mössbauer spectroscopy.

Rats have been enriched in 57Fe and erythrocytes were isolated from the blood. Mössbauer absorption spectroscopy on the hemoglobin of these erythrocytes has shown rather similar dynamics as found earlier in crystals of myoglobin, in frozen solutions of human hemoglobin and in a number of other proteins. The results strongly indicate that the motion of the heme and presumably some part of the F-helix is mainly influenced by the average viscosity of the sample determined by a network of hydrogen bridges and other weak interactions. Extrapolations of Mössbauer results from protein crystals to proteins in their physiological surroundings seem to be suitable for heme proteins.

Animals↗
PubMed1992

Influence of protein dynamics on the metal-sites of ovotransferrin.

Using the perturbed angular correlations (PAC) technique, the formation of hafnium-ovotransferrin complexes has been studied. Two binding configurations at each of the two specific binding-sites of the protein have been observed. They are characterized by well-defined electric quadrupole frequencies. Information about the dynamics of the protein was derived from temperature dependent measurements of the relaxation constant. The well-resolved spectra taken with fast BaF2-detectors allow a precise determination of the relaxation behaviour of the protein. The results are compared with the predictions from a hydrodynamic model for the reorientation of macromolecules. Thus the hydrodynamic volume of ovotransferrin and its N-terminal half-molecule were determined. The ovotransferrin volume is in agreement with a value derived for human serum transferrin from small angle neutron scattering. From experiments with immobilized protein material there is evidence for internal protein dynamics which is probed by the Hf-ion bound to the specific metal-sites.

Animals↗
PubMed1993

Identification and characterization of the iron compounds in bone marrow by means of Mössbauer spectrometry.

In order to determine and to demonstrate the cellular iron molecular states in hematopoietic bone marrow, direct investigations were performed by means of different and complementary spectroscopic techniques: optical absorption, electron spin resonance and Mössbauer spectrometry. In fact, the latter appears to have been the most informative. In addition to the hemoglobin forms, five- and six-coordination ligand protoporphyrins IX (monomeric and polymeric stacking, respectively) were observed. A small amount of non-hemic high-spin iron III storage component (ferritin) was measured. No diferric transferrin was detected. A ferrous compound was also observed and attributed to the mitochondrial iron pool.

Bone Marrow↗
PubMed1988

Ferricrocin functions as the main intracellular iron-storage compound in mycelia of Neurospora crassa.

Neurospora crassa produces several structurally distinct siderophores: coprogen, ferricrocin, ferrichrome C and some minor unknown compounds. Under conditions of iron starvation, desferricoprogen is the major extracellular siderophore whereas desferriferricrocin and desferriferichrome C are predominantly found intracellularly. Mössbauer spectroscopic analyses revealed that coprogen-bound iron is rapidly released after uptake in mycelia of the wild-type N. crassa 74A. The major intracellular target of iron distribution is desferriferricrocin. No ferritin-like iron pools could be detected. Ferricrocin functions as the main intracellular iron-storage peptide in mycelia of N. crassa. After uptake of ferricrocin in both the wild-type N. crassa 74A and the siderophore-free mutant N. crassa arg-5 ota aga, surprisingly little metabolization (11%) could be observed. Since ferricrocin is the main iron-storage compound in spores of N. crassa, we suggest that ferricrocin is stored in mycelia for inclusion into conidiospores.

Biological Transport, Active↗
PubMed1988

Mössbauer studies of electrophoretically purified monoferric and diferric human transferrin.

Electrophoretically purified 57Fe-enriched monoferric and diferric human transferrins and selectively labeled complexes ([C-56Fe,N-57Fe]transferrin and [C-57Fe,N-56Fe]transferrin) were studied by Mössbauer spectroscopy. The data were recorded at 4.2 K over a wide range of applied magnetic fields (0.05-6 T) and were analyzed by a spin-Hamiltonian formalism. Characteristic hyperfine parameters were found and the obtained zero-field splitting parameters (D = 0.25 +/- 0.05 cm-1 and E/D = 0.30 +/- 0.02) agree with previous electron paramagnetic resonance (EPR) findings. The weak-field spectra of the [N-57Fe]transferrin are slightly broader than those of the [C-57Fe]transferrin, indicating that the N-terminal iron site may be more heterogeneous. However, the absorption line positions and the relative intensities of the subspectra originating from the three Kramers doublets of each Fe3+ site are identical. Thus the electronic structures of the two iron sites can be described by the same set of spin-Hamiltonian parameters, indicating that the ligand environments for the two sites are the same, as suggested by the recent X-ray crystallographic studies. This suggestion is further supported by the observation that the strong-field spectra of the two monoferric transferrins are indistinguishable. The selectively labeled mixed-isotope transferrins exhibit spectra that are identical to those of the corresponding monoferric 57Fe-enriched transferrins, implying that the occupation of one iron site has little or no effect on the immediate environment of the other site, a finding that is not surprising since the two sites are separated by approximately 4.2 nm.

Binding Sites↗
PubMed1988

Studies on haemosiderin and ferritin from iron-loaded rat liver.

Haemosiderin has been isolated from siderosomes and ferritin from the cytosol of livers of rats iron-loaded by intraperitoneal injections of iron-dextran. Siderosomal haermosiderin, like ferritin, was shown by electron diffraction to contain iron mainly in the form of small particles of ferrihydrite (5Fe2O3.9H2O), with average particle diameter of 5.36 +/- 1.31 nm (SD), less than that of ferritin iron-cores (6.14 +/- 1.18 nm). Mössbauer spectra of both iron-storage complexes are also similar, except that the blocking temperature, TB, for haemosiderin (23 K) is lower than that of ferritin (35 K). These values are consistent with their differences in particle volumes assuming identical magnetic anisotropy constants. Measurements of P/Fe ratios by electron probe microanalysis showed the presence of phosphorus in rat liver haemosiderin, but much of it was lost on extensive dialysis. The presence of peptides reacting with anti-ferritin antisera and the similarities in the structures of their iron components are consistent with the view that rat liver haemosiderin arises by degradation of ferritin polypeptides, but its peptide pattern is different from that found in human beta-thalassaemia haemosiderin. The blocking temperature, 35 K, for rat liver ferritin is near to that reported, 40 K, for human beta-thalassaemia spleen ferritin. However, the haemosiderin isolated from this tissue, in contrast to that from rat liver, had a TB higher than that of ferritin. The iron availability of haemosiderins from rat liver and human beta-thalassaemic spleen to a hydroxypyridinone chelator also differed. That from rat liver was equal to or greater, and that from human spleen was markedly less, than the iron availability from either of the associated ferritins, which were equivalent. The differences in properties of the two types of haemosiderin may reflect their origins from primary or secondary iron overload and differences in the duration of the overload.

Animals↗
PubMed1990

A Mössbauer spectroscopy study of cellular acquisition of iron from pyoverdine by Pseudomonas aeruginosa.

Mössbauer spectroscopy was used to investigate the cellular acquisition of iron by Pseudomonas aeruginosa which had been incubated with ferripyoverdine for 20, 40, 60, 120 or 360 min. Studies revealed that no ferripyoverdine accumulated in the cells at any of these times and that the amounts and kinds of iron complexes produced by cellular metabolism vary with time. At 20 and 40 min a ferric species, with isomer shift delta = 0.38-0.42 mm/s and quadrupole splitting delta EQ = 0.94-0.92 mm/s, was the major iron metabolite comprising approximately 80% of the iron. At later times at least three other ferric species appeared with delta = 0.54----0.72, delta EQ = 0.84----1.07 mm/s. Ferrous species, delta = 1.43----1.77 mm/s and delta EQ = 2.69----1.82 mm/s, were also seen at times as early as 20 min and comprised as much as 17% of the total iron at 20 and 40 min. The parameters of all these species identify them as being six-coordinated high-spin complexes. In addition a low-spin species, delta = 0.19 mm/s delta EQ = 0.67----0.91 mm/s, never before reported in cells, appeared at 60, 120, and 360 min as one of the major iron metabolites (50% or more). All isomer shifts are measured with respect to natural iron.

Iron↗
PubMed1991

Transport and utilization of ferrioxamine-E-bound iron in Erwinia herbicola (Pantoea agglomerans).

We have analyzed ferrioxamine-E-mediated iron uptake and metabolization in Erwinia herbicola K4 (Pantoea agglomerans) by means of in vivo Mössbauer spectroscopy and radioactive labeling techniques. A comparison of cell spectra with the spectrum of ferrioxamine clearly demonstrates that ferrioxamine E is not accumulated in the cell, indicating a fast metal transfer. Only two major components of iron metabolism can be detected, a ferric and a ferrous species. At 30 min after uptake, 86% of the internalized metal corresponded to a ferrous ion compound and 14% to a ferric iron species. Metal transfer apparently involves a reductive process. With progressing growth, the oxidized species of the two major proteins becomes dominant. The two iron metabolites closely resemble species previously isolated from Escherichia coli. These components of iron metabolism differ from bacterio-ferritin, cytochromes and most iron-sulfur proteins. All other iron-containing cellular components are at least one order of magnitude lower in concentration. We suggest that the ferrous and ferric iron species correspond to two different oxidation states of a low-molecular mass protein.

Biological Transport↗
PubMed1991

Mössbauer effect study of gamma-irradiated human oxyhemoglobin.

Preliminary results of the Mössbauer effect study of human adult oxyhemoglobin in erythrocytes exposed to gamma-irradiation with doses of approximately 100, approximately 300 and approximately 600 kGy are presented. Mössbauer spectra measured at 87 K have been analyzed in two ways. At first, to fit these spectra we used the four components oxyhemoglobin, deoxyhemoglobin, hemochromes and non-heme Fe(III) compound which had been obtained earlier from Mössbauer spectra of X-irradiated oxyhemoglobin by Chevalier et al. (1983). However, this approximation was not satisfactory. Then a new model of spectral fitting with five components was used. These were oxyhemoglobin, deoxyhemoglobin and components marked 1, 2 and 3. Using Mössbauer hyperfine parameters of each component the valence/spin states of iron ions were determined and possible complexes were considered. The most probable compounds for components 1, 2 and 3 were hematin and/or mu-oxodimers, methemoglobin hydroxide and/or hemichromes, and the high spin Fe(III) complex, respectively. Changes of the relative areas of Mössbauer subspectra of all components (its content in samples) versus doses were evaluated and the presence of the high and low spin aquomethemoglobin was indicated.

Adult↗
PubMed1994

Study of a low-selenium environment in China by INAA and Mössbauer spectrometry.

The neutron activation analysis, gamma coincidence spectroscopy, nondispersive hydrogen flame atomic fluorescence spectroscopy, and Mössbauer spectrometry were used to study the low-selenium environment of the Exi Autonomous Prefecture, a well-known Keshan disease region. The Se contents in the soil samples there range from 0.075-0.18 mg/kg with the average of 0.13 mg/kg, whereas in the maize from 0.001-0.018 mg/kg with the average of 0.0099 mg/kg. The 57Fe Mössbauer spectrum of the soil indicates an anoxic environment. In addition to the FE3+ species the compounds containing low-valence iron e.g., goethite, and so forth, also exist. The rare earth element (REE) pattern obtained by NAA further confirms the reductive soil environment, which causes the selenium deficiency.

China↗
PubMed2001

Trace cobalt speciation in bacteria and at enzymic active sites using emission Mössbauer spectroscopy.

57Co emission Mössbauer spectroscopy (EMS) allows the chemical state of cobalt, as influenced by its coordination environment, to be monitored in biological samples at its physiological (trace) concentrations. To draw attention to EMS as a valuable tool for speciation of cobalt in biocomplexes, the process of cobalt(II) metabolism in cells of the plant growth-promoting rhizobacterium Azospirillum brasilense Sp245 was investigated using EMS of 57CoII-doped bacterial cells. EMS measurements also showed 57CoII-activated glutamine synthetase (GS, a key enzyme of nitrogen metabolism, isolated from this bacterium) to have two different cobalt(II) forms at its active sites, in agreement with data available on other bacterial GSs. Chemical after-effects following electron capture by the nucleus of the parent 57CoII during the 57Co-->57Fe transition, which contribute to the formation of a stabilised daughter 57FeIII component along with the nucleogenic 57FeII forms, are also briefly considered.

Azospirillum brasilense↗