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PubMed1995

Mössbauer spectroscopy on nonequilibrium states of myoglobin: a study of r-t relaxation.

A frozen solution of 57Fe-enriched metmyoglobin was irradiated by x rays at 77 K. Mössbauer spectra showed a reduction of Fe(III) high spin by thermalized electrons and a production of a metastable Fe(II) low spin myoglobin complex with H2O at its sixth coordination site. The relaxation of the intermediate was investigated by Mössbauer spectroscopy as a function of temperature and time. The relaxation process starts above 140 K and is fully completed at approximately 200 K. At temperatures between 140 and 200 K, the relaxation lasts for hours and is nonexponential in time. Up to 180 K, the process can be described satisfactorily by a gamma distribution of activation enthalpies with an Arrhenius relation for the rate coefficient. The temperature and time dependence of the Mössbauer parameters indicates structural changes in the active center of the protein as early as 109 K that continue for several hours at higher temperatures. Above 180 K, structural rearrangements involving the whole protein molecule lead to a shift and narrowing of the barrier height distribution.

Animals↗
PubMed1999

Heme-solvent coupling: a Mössbauer study of myoglobin in sucrose.

The Mössbauer effect of 57Fe-enriched samples was used to investigate the coupling of 80% sucrose/water, a protein-stabilizing solvent, to vibrational and diffusive modes of the heme iron of CO-myoglobin. For comparison we also determined the Mössbauer spectra of K4 57Fe (CN)6 (potassium ferrocyanide, PFC), where the iron is fully exposed in the same solvent. The temperature dependence of the Mössbauer parameters derived for the two samples proved to be remarkably similar, indicative of a strong coupling of the main heme displacements to the viscoelastic relaxation of the solvent. We show that CO escape out of the heme pocket couples to the same type of fluctuations, whereas intramolecular bond formation involves solvent-decoupled heme deformation modes that are less prominent in the Mössbauer spectrum. With respect to other solvents, however, sucrose shows a reduced viscosity effect on heme displacements and the kinetics of ligand binding due to preferential hydration of the protein. This result confirms thermodynamic predictions of the stabilizing action of sucrose by a dynamic method.

Animals↗
PubMed2002

Recombinant Escherichia coli biotin synthase is a [2Fe-2S](2+) protein in whole cells.

EPR and Mössbauer spectroscopies have been used to determine the type and properties of the iron-sulfur clusters present in homologously expressed recombinant Escherichia coli BioB in whole cells prior to purification. Difference EPR spectra of samples of whole cells from a strain over-expressing E. coli BioB and a strain containing the same plasmid but without the bioB insertion showed an axial S=1/2 resonance that was attributed to the [2Fe-2S](+) cluster of the E. coli iron-sulfur cluster assembly 2Fe ferredoxin, based on principal g-values, linewidths and relaxation behavior. Comparison of the Mössbauer spectra of whole cells with and without the bioB insertion revealed that the E. coli cells with over-expressed BioB contain an additional species that exhibits a spectrum identical to that of the [2Fe-2S](2+) cluster in purified recombinant BioB. The concentration of this [2Fe-2S](2+) species in the whole cell sample was quantified using a Mössbauer standard and found to be approximately 260 microM, which was comparable to the BioB protein concentration estimated for the cell paste. The results demonstrate that the [2Fe-2S](2+) cluster found in purified samples of recombinant BioB is not an artifact of the protein purification procedure, and indicate that recombinant BioB is over-expressed in an inactive form during aerobic growth.

Electron Spin Resonance Spectroscopy↗
PubMed2003

Mössbauer studies of the non-heme iron and cytochrome b559 in a Chlamydomonas reinhardtii PSI- mutant and their interactions with alpha-tocopherol quinone.

Spin and valence states of the non-heme iron and the heme iron of cytochrome b559, as well as their interactions with alpha-tocopherol quinone (alpha-TQ) in photosystem II (PSII) thylakoid membranes prepared from the Chlamydomonas reinhardtii PSI- mutant have been studied using Mössbauer spectroscopy. Both of the iron atoms are in low spin ferrous states. The Debye temperature of the non-heme is 194 K and of the heme iron is 182 K. The treatment of alpha-TQ does not change the spin and the valence states of the non-heme iron but enhances the covalence of its bonds. alpha-TQ oxidizes the heme iron into the high spin Fe3+ state. A possible role of the non-heme iron and alpha-TQ in electron flow through the PSII is discussed.

Animals↗
PubMed1997

Highly purified D1/D2/cyt b559 preparations from spinach do not contain the non-heme iron center.

57Fe enriched D1/D2/cyt b559 preparations were isolated from spinach grown hydroponically on a 57Fe containing medium. In terms of polypeptide and pigment composition these samples are of high purity and functional integrity of P680. Mössbauer spectra measured in D1/D2/cyt b559 complexes revealed that these preparations are completely deprived of the non-heme iron center. Possible implications of this finding are discussed for the electron transfer from Pheo-. to exogenous electron acceptors.

Cytochrome b Group↗
PubMed1999

Inorganic Fe2+ formation upon Fe-S protein thermodestruction in the membranes of thermophilic cyanobacteria: Mössbauer spectroscopy study.

A model description of the Mössbauer spectrum (80 K) of native membranes of the thermophilic cyanobacterium Synechococcus elongatus is suggested on the basis of the known values of quadrupole splitting (deltaE(Q)) and isomer shift (deltaFe) for the iron-containing components of the photosynthetic apparatus. Using this approach, we found that heating the membranes at 70-80 K results in a decrease of doublet amplitudes belonging to F(X), F(A), F(B) and ferredoxin and simultaneous formation of a new doublet with deltaE(Q) = 3.10 mm/s and delta-Fe = 1.28 mm/s, typical of inorganic hydrated forms of Fe2+. The inhibition of electron transfer via photosystem I to oxygen, catalyzed by ferredoxin, occurs within the same range of temperatures. The data demonstrate that the processes of thermoinduced Fe2+ formation and distortions in the photosystem I electron transport in the membranes are interrelated and caused mainly by the degradation of ferredoxin. The possible role of Fe2+ formation in the damage of the photosynthetic apparatus resulting from heating and the action of other extreme factors is discussed.

Bacterial Proteins↗
PubMed1999

Mössbauer studies of Escherichia coli biotin synthase: evidence for reversible interconversion between [2Fe-2S](2+) and [4Fe-4S](2+) clusters.

The nature and properties of the iron-sulphur (Fe-S) cluster in as-prepared and reduced biotin synthase of Escherichia coli have been investigated by Mössbauer spectroscopy. Our data clearly demonstrate that in the as-prepared sample, the cluster is present as [2Fe-2S](2+) with isomer shift, delta = 0.29 mm/s and quadrupole splitting, DeltaE(Q) = 0.53 mm/s, indicating incomplete cysteinyl-S coordination. Anaerobic reduction by dithionite in the presence of 55% (v/v) glycerol converts this form to [4Fe-4S](2+) (delta = 0.45 mm/s and DeltaE(Q) = 1.11 mm/s) and is accompanied by some destruction to Fe(2+). This cluster conversion is reversible and when exposed to air, the [4Fe-4S](2+) cluster is quantitatively reconverted to the [2Fe-2S](2+) cluster without any further cluster degradation.

Air↗
PubMed2002

Superoxide reductase activities of neelaredoxin and desulfoferrodoxin metalloproteins.

Superoxide reductases have now been well characterized from several organisms. Unique biochemical features include the ability of the reduced enzyme to react with O2- but not dioxygen (reduced SORs are stable in an aerobic atmosphere for hours). Future biochemical assays that measure the reaction of SOR with O2- should take into account the difficulties of assaying O2- directly and the myriad of redox reactions that can take place between components in the assay, for example, direct electron transfer between cytochrome c and Dfx. Future prospects include further delineation of the reaction mechanisms, characterization of the putative (hydro)peroxo intermediate, and studies that uncover the components between reduced pyridine nucleotides and SOR in the metabolic pathway responsible for O2- detoxification.

Amino Acid Sequence↗
PubMed2000

Characterization of the heme iron in pyridoxylated hemoglobin cross-linked by glutaraldehyde using Mössbauer spectroscopy.

The heme iron in human adult hemoglobin modified by both pyridoxal-5'-phosphate and glutaraldehyde was characterized by Mössbauer spectroscopy and compared with non-modified hemoglobin. Mössbauer spectra of the samples were measured at 87 and 295 K (1yophilized form) and at 87 K (frozen solution). The values of quadrupole splitting for the oxy-form of modified hemoglobin were found to be lower than those of the oxy-form of hemoglobin without modifications in lyophilized form and frozen solution, respectively. On the other hand, the values of quadrupole splitting for the deoxy-form of modified and non-modified hemoglobins in frozen solution were the same. The Mössbauer spectra of the oxy-form of modified hemoglobin were also analyzed in terms of the heme iron non-equivalence in alpha- and beta-subunits of tetramer. The differences of the tendencies of temperature dependencies of quadrupole splitting for the oxy-form of modified and non-modified hemoglobins in lyophilized form were shown. These results indicated that the heme iron electronic structure and stereochemistry were changed in the oxy-form of pyridoxylated hemoglobin cross-linked by glutaraldehyde.

Adult↗
PubMed2001

Hyperfine interactions in the iron cores from various pharmaceutically important iron-dextran complexes and human ferritin: a comparative study by Mössbauer spectroscopy.

Mössbauer spectroscopy has been used to study the hyperfine interactions in the iron cores of pharmaceutically important industrial and elaborated iron-dextran complexes (ferritin models) and human ferritin. Mössbauer spectra of frozen solutions and lyophilized samples of iron-dextran complexes at 87 K demonstrated magnetic, superparamagnetic and paramagnetic states of iron in various complexes. Mössbauer spectra of human ferritin in frozen solution and lyophilized form showed paramagnetic state of iron at 87 K. Small variations of Mössbauer hyperfine parameters were observed for different samples at 87 and 295 K, respectively, supposing the homogenous iron cores. The values of quadrupole splitting for iron-dextran complexes and ferritin in frozen solutions at 87 K varied from 0.639 to 0.744 mm/s while those of lyophilized samples at 87 K varied from 0.714 to 0.788 mm/s. The values of quadrupole splitting for iron-dextran complexes and ferritin in lyophilized form at 295 K varied from 0.687 to 0.741 mm/s. The values of hyperfine magnetic fields on the 57Fe nuclei in several iron-dextran complexes at 87 K varied from approximately 231 to approximately 485 kOe. These small variations of the hyperfine parameters were related to several types of the hydrous iron oxide microstructural modifications in the core and variations of the iron core size. The influence of lyophilization on the iron core structure was also assumed. In addition, Mössbauer spectra were evaluated in supposition of heterogeneous iron core in all samples.

Dextrans↗
PubMed2000

Preparation, characterization, and performance of magnetic iron-carbon composite microparticles for chemotherapy.

Magnetic microcarrier particles useful for delivering chemotherapeutic drug molecules are described. The particles are formed by joint deformation of iron and carbon in a ball mill. Physical, chemical, and functional characterization has been carried out on the particles. Physical characteristics include microscopy, particle size analysis (0.5-5 microm), surface area (250 m2/g), water vapor adsorption isotherm (hydrophobic surface), and analysis of the iron-carbon interface by Mössbauer spectroscopy, X-ray diffraction, and differential thermal analysis. Chemical analysis was used to identify elements in the particles other than carbon and iron. Functional characteristics measured included the particles' ability to adsorb and desorb doxorubicin, cytotoxicity, and their magnetic susceptibility.

Adenocarcinoma↗
PubMed2001

Potentiometric and spectroscopic studies on the dimethyltin(IV) complexes of 2-hydroxyhippuric acid.

Equilibrium and spectroscopic (1H, 13C NMR and 119Sn Mössbauer) studies in aqueous solution are reported for dimethyltin(IV) complexes of 2-hydroxyhippuric acid (Sal-Gly). Below pH 4, oxygen-coordinated complexes MLH and ML are formed. In the pH range 5-8.5, the species MLH(-1), predominates at any metal-to-ligand ratio. The ligand exchange of this species is slow on the NMR time scale, which allows its structural characterization by NMR spectroscopy: the coordination polyhedron around the tin atom is distorted trigonal bipyramidal, with tridentate [O-,N-,COO-] coordination of Sal-Gly, involving two equatorial methyl groups. The NMR results reveal that the main cause of the distortion of the polyhedron is the large CH3-Sn-CH3 angle of 136+/-4 degrees. The presented results supplement the data available on the dimethyltin(IV)-promoted amide deprotonation of peptides, and provide further arguments for the fundamental role of the carboxylate as an anchoring group in this process.

Electrochemistry↗
PubMed2002

The dynamics of (57)Fe nuclei in Fe(III)-DNA condensates.

The dynamics of iron nuclei in the condensates obtained by interaction of Fe(III) with DNA, Fe(III)(DNA monomer)(2), have been investigated by variable temperature (57)Fe Mössbauer spectroscopy. Studies were effected on gel and freeze-dried samples, obtaining nearly coincident values of the parameters isomer shift and nuclear quadrupole splitting in T ranges 20-260 K. Functions ln(A(T)/A(77.3)) vs. T, here employed to investigate the dynamics of Fe nuclei, showed linear trends in the T ranges 20-150 and 150-260 K, respectively, the latter with larger slopes. Data coincided for gelled and freeze-dried specimens. No variation of delta or Delta E parameters occurred at the two T intervals, which suggests constancy of structure and bonding with the temperature changes. Functions (T) showed trends analogous to the corresponding functions determined for iron proteins, which were attributed to the occurrence of 'conformational substates'.

Animals↗
PubMed2002

Coordination properties of adenosine-5'-monophosphate and related ligands towards Me2Sn(IV)2+ in aqueous solution.

The coordination of Me2Sn(IV)2+ to adenosine-5'-monophosphate (AMP) and the related compounds D-ribose-5-phosphate (R5P), D-glucose-1-phosphate (G1P) and D-glucose-6-phosphate (G6P) in aqueous solution was investigated by means of potentiometric titration, and 1H-, 31P-NMR and Mössbauer spectroscopic methods in the pH range 2-11 (I=0.1 M NaClO4, 298 K). The complex of AMP and Me2Sn(IV)2+ precipitated at low pH was characterised by elemental analysis, FT-IR and Mössbauer spectroscopic methods. From a comparison of the pK values obtained in the presence and absence of metal ion and the stability constants for the different systems, the coordination of [N] is excluded, while bidentate coordination of the phosphate group is presumed. Mössbauer spectroscopic measurements recorded in the glassy state confirmed bidentate coordination of the phosphate and the formation of mixed hydroxo complexes in the weakly acidic, neutral and strongly basic pH range. With increasing pH, the phosphate groups were replaced by the deprotonated alcoholic [O] atoms of the sugar moiety. The solid complex proved to be tbp structure with bidentate phosphate coordination.

Adenosine Monophosphate↗
PubMed2002

The dynamics of 57Fe nuclei in Fe(II)-DNA and [Fe(II)(1-methyl-2-mercaptoimidazole)2]-DNA condensates.

Alcoholic solutions of FeCl(2) and Fe(II)(Hmmi)(2)Cl(2) (Hmmi=1-methyl-2-mercaptoimidazole) induce calf thymus DNA condensation from aqueous solutions buffered at pH 7.4. A 1:1 Fe(II)-(DNA monomer) stoichiometry is assumed. The (57)Fe Mössbauer hyperfine parameters suggest an octahedral coordination environment, severely distorted, in both Fe(II)-(DNA monomer) and [Fe(II)(Hmmi)(2)]-(DNA monomer) condensates. The dynamic properties of iron nuclei in freeze-dried samples were investigated by means of variable temperature (57)Fe Mössbauer spectroscopy. Mean square displacements, (T), were calculated, such as the effective vibrating mass and the Mössbauer lattice temperature of the solids. increases linearly with the temperature in the whole temperature range explored; the absolute values are typical for lattice or solid-state vibrations. Very similar values for the effective vibrating masses were extracted, suggesting comparable covalency of the bonding interaction between the metal atom and its ligands, while the Mössbauer lattice temperatures show a softening of the lattice for [Fe(II)(Hmmi)(2)]-(DNA monomer) with respect to Fe(II)-(DNA monomer) condensate.

Animals↗
PubMed2003

Reactions of site-differentiated [Fe4S4]2+, 1+ clusters with sulfonium cations: reactivity analogues of biotin synthase and other members of the S-adenosylmethionine enzyme family.

The first examples of reduced 3:1 site-differentiated Fe(4)S(4) clusters have been synthesized as [Fe(4)S(4)(LS(3))(SR')](3-) (R=Et, Ph) by chemical reduction of previously reported [Fe(4)S(4)(LS(3))(SR')](2-) clusters, and isolated as NBu(4)(+) salts. The reduced clusters were characterized by electrochemistry and EPR, 1H NMR, and Mössbauer spectroscopies. The reaction of oxidized clusters with the sulfonium ions [PhMeSCH(2)R](+) (R=COPh, p-C(6)H(4)CN) in acetonitrile results in electrophilic attack on coordinated thiolate and production of PhSMe and R'SCH(2)R when the reaction occurs at the unique cluster site. The reactions of reduced clusters with these substrates were examined in relation to the reductive cleavage of the cofactor S-adenosylmethionine, the first step in the catalytic cycle of biotin synthase. Product analysis indicated a approximately 4:1 ratio of reductive cleavage to electrophilic attack. The cleavage products are PhSMe, R'SCH(2)R, and RCH(3) for both clusters, and also PhMeS=CHR and RCH(2)CH(2)R from secondary reactions when the sulfonium cation is [PhMeSCH(2)COPh](+) and [PhMeSCH(2)-p-C(6)H(4)CN](+), respectively. Reaction schemes for reductive cleavage based on product distributions are presented. These results parallel those previously reported for homoleptic [Fe(4)S(4)(SR')(4)](2-,3-) clusters and demonstrate that site-differentiated clusters sustain a high percentage of reductive cleavage, a necessary result in the context of biotin synthase activity preceding an investigation of the mode of binding of sulfonium substrates and inhibitors at the unique iron site. [LS(3)=1,3,5-tris[(4,6-dimethyl-3-mercaptophenyl)thio]-2,4,6-tris(p-tolylthio)benzene(3-)].

Binding Sites↗