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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interactions of horse spleen ferritin and its derivative apoferritin with H+ ions were studied by potentiometric and spectrophotometric titration; to aid in data analysis, heats of ionization over a limited pH range and amide content were also determined. Per apoferritin subunit, all tyrosine and cysteine side chains, two of the nine lysine side chains and at least three of the six histidine side chains were found not to titrate; a preliminary but self-consistent analysis of the titration data is proposed. The titration curve of ferritin was identical with that of apoferritin in the pH range 5.5 to 3. In addition, under the conditions used, the reactivities of ferritin histidines to bromoacetate and of ferritin lysines to formaldehyde were identical with those in apoferritin. Above pH 8, a time-dependent titration of the ferritin core occurs which prevents comparison of the titration curves of the two proteins in this region. However, in the pH regions 5.5 to 7.5, two extra groups per subunit titrate reversibly in ferritin relative to apoferritin. Moreover, although the isoionic points of ferritin and apoferritin are identical in water, the isoionic point of ferritin is 0.5 pH unit lower than that of apoferritin in 0.16 to 1 M KCl. The different effects of KCl and NaCl on the two proteins indicate the presence of cation binding sites in ferritin that are absent in apoferritin and possibly also the presence of anion binding sites in apoferritin that are occupied in ferritin by anions of the core. The difference between the isoionic points of the two proteins in KCl has been interpreted to indicate the presence of approximately 2 phosphate residues per ferritin subunit which serve as cation binding sites and which are negatively charged at the isoionic point in KCl. These phosphates may also represent the additional residues that titrate in ferritin between pH 5.5 and 7.5, or may interact with positively charged residues on the inner surface of the ferritin shell, or both.
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PMID:Hydrogen ion interactions of horse spleen ferritin and apoferritin. 1 Dec 12

Transformation for capsular-types (A and B) between four Staphylococcus aureus strains was attempted using a serum-soft agar technique to distinguish the capsular-type. DNA preparations from the Smith diffuse strain (capsular-type A) transformed strain NS58C (unencapsulated variant of capsular-type B) to type A. The strain NS58C required Ala- and His-, however, the two transformants tested were Ala+ and His+. These properties coincided with those of the donor strain just as the following characters of the transformants, which are quite different from the untransformed recipient cells: i) negative clumping factor reaction, ii) diffuse-type growth in serum-soft agar, and iii) high mouse virulence. The change to capsular-type A was antigenically comfirmed by electronmicroscopy using ferritin conjugated anti-capsular antibody.
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PMID:Encapsulation by transformation of strains of Staphylococcus aureus determined by the serum-soft agar technique. 37 20

The reversion of protoplasts of Bacillus licheniformis 6346 His- on a medium containing 2.5% agar has been studied in sectioned material after reaction with a ferritin-conjugated antibody specific to the peptidoglycan isolated from the walls of the bacilli. Freeze etching has also been used. Fibrils of material reacting with the antibody have been detected emerging from isolated areas of the protoplasts after 3 h of incubation. This material gradually covers the cell and can eventually (at 6 h) be seen in freeze-etched preparations as a fringe of up to 400 nm around the cells and covering the surfaces with particles that can be removed by lysozyme. At later stages the wall begins to take on a compact, well-defined appearance that can be seen in sections; however, the cells are still grossly deformed. A transitory emergence, beyond the wall of long fibers of 6 nm in diameter, takes place after about 12 h of incubation. These fibers react with the conjugated antibody and after freeze etching show a regular banded structure. They are probably indentical with the fibers isolated elsewhere (Elliott et al., 1975) and shown to contain all the wall constituents (i.e., peptidoglycan, teichoic acid, and teichuronic acid). These fibers are not detectable in the final stages of reversion.
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PMID:Ultrastructural study of the reversion of protoplasts of Bacillus licheniformis to bacilli. 118 77

Horse spleen ferritin will bind up to 16 protoporphyrin IX haem groups per 24 subunits in vitro [Kadir & Moore (1990) FEBS Lett. 276, 81-84] at a site that causes the haem to be low spin for both ferric and ferrous states. E.p.r. spectra at 10 K of the oxidized form of the resulting haemoferritin gives g values of 2.93, 2.26 and 1.55, characteristic of low-spin haem. The near-i.r. magnetic circular dichroism spectrum shows a porphyrin-to-ferric charge-transfer band at 1590 nm. The spectroscopic parameters indicate that the haem group is probably bound by two histidine ligands. Molecular modelling studies reveal one type of potential haem-binding site in horse L-chain ferritin with bis-histidine co-ordination. This is an intersubunit site which lies in a pocket within the ferritin protein shell in the region of the 3-fold channel. The ligands are His-114 and His-124 in horse L-chain. A second possible set of sites in human H-chain ferritin involves His-60 residues in the pockets between pairs of subunits. These are considered less likely sites of haem occupancy. There are three of the intersubunit sites in horse L-chain ferritin at each of the eight 3-fold channels. We propose that conformational crowding between haem-binding sites at a given channel prevents more than two haems per channel being bound.
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PMID:Spectroscopic identification of the haem axial ligands of haemoferritin and location of possible haem-binding sites in ferritin by molecular modelling. 133 74

A 64-year-old man was admitted due to ascites. Laboratory data showed hemoglobin 6.7 g/dl, mean corpuscular volume 82 fl, and ferritin 2,360 ng/ml. Liver biopsy showed hemochromatosis. The diagnosis of beta-thalassemia was suggested by a decreased ratio of beta/alpha-globin synthesis in vitro (0.26). Cloning of the beta-globin gene showed A-to-G mutation in the first base of the ATA box. He was confirmed to be homozygous for this specific allele by beta-gene complex analysis and analysis of Southern blot hybridization of the alpha- and beta-globin genes. His two sons were confirmed to be heterozygous for this allele.
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PMID:Beta(+)-thalassemia with hemochromatosis. 136 99

The iron storage protein, ferritin, is widely distributed in the living kingdom. Here the complete cDNA and derived amino-acid sequence of pea seed ferritin are described, together with its predicted secondary structure, namely a four-helix-bundle fold similar to those of mammalian ferritins, with a fifth short helix at the C-terminus. An N-terminal extension of 71 residues contains a transit peptide (first 47 residues) responsible for plastid targetting as in other plant ferritins, and this is cleaved before assembly. The second part of the extension (24 residues) belongs to the mature subunit; it is cleaved during germination. The amino-acid sequence of pea seed ferritin is aligned with those of other ferritins (49% amino-acid identity with H-chains and 40% with L-chains of human liver ferritin in the aligned region). A three-dimensional model has been constructed by fitting the aligned sequence to the coordinates of human H-chains, with appropriate modifications. A folded conformation with an 11-residue helix is predicted for the N-terminal extension. As in mammalian ferritins, 24 subunits assemble into a hollow shell. In pea seed ferritin, its N-terminal extension is exposed on the outside surface of the shell. Within each pea subunit is a ferroxidase centre resembling those of human ferritin H-chains except for a replacement of Glu-62 by His. The channel at the 4-fold-symmetry axes defined by E-helices, is predicted to be hydrophilic in plant ferritins, whereas it is hydrophobic in mammalian ferritins.
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PMID:Amino-acid sequence and predicted three-dimensional structure of pea seed (Pisum sativum) ferritin. 147 6

This study compared the effect of loading apoferritin either with ferrous ammonium sulfate in various buffers or with ceruloplasmin and chelated ferrous iron. It was shown that loading of apoferritin with ferrous ammonium sulfate was dependent on buffer and pH, and was directly related to the rate of iron autoxidation. The ceruloplasmin-dependent loading of apoferritin, however, was unaffected by these factors. Isoelectric focusing and amino acid analysis of the differently loaded ferritins showed that ferrous ammonium sulfate loading of apoferritin resulted in the depletion of the basic amino acids, lysine and histidine, probably as a result of protein oxidation. No significant differences in amino acid composition was noted for ceruloplasmin-loaded ferritin. Furthermore, ferritin loaded with ferrous ammonium sulfate released more iron than either native or ceruloplasmin-loaded ferritin when either paraquat or EDTA was used as an iron mobilizing agent. We suggest that the loading of apoferritin with ferrous ammonium sulfate occurred as a result of iron autoxidation and may result in oxidation of amino acids and loss of integrity of the protein, and that ceruloplasmin may act as a catalyst for the incorporation of iron into apoferritin in a manner more closely related to that occurring in vivo.
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PMID:In vitro loading of apoferritin. 153 76

This study demonstrates the ability of aqueous extracts of cigarette smoke to reduce iron and cause its release from ferritin. Superoxide dismutase (SOD) increases the rates of iron release with the less filtered smoke extracts, but has no effect on the rate of iron release caused by aqueous extracts of well-filtered gas-phase cigarette smoke. Faster rates of iron release are observed under anaerobic conditions, and the reducing power of the cigarette smoke extracts is prolonged when incubated in argon. Hydroquinone and catechol, two of the major polyhydroxybenzenes in cigarette smoke, increase in concentration in the smoke extracts as these are subjected to less filtration, and higher concentrations of polyhydroxybenzenes correlate with higher rates of iron release from ferritin. Concomitant with iron release, depletions of amino acids in ferritin are observed. Depletion of histidine is partially prevented by bathophenanthrolinedisulfonate and mannitol, while lysine and arginine depletions remain unaffected. These observations suggest that cigarette smoke components react directly with these amino acid residues in ferritin. Cigarette smoke induced release of iron could alter iron metabolism in the lungs of chronic smokers and contribute to the increase in the total oxidative burden on the lungs of smokers.
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PMID:Release of iron from ferritin by aqueous extracts of cigarette smoke. 158 27

The role of the protein shell in the formation of the hydrous ferric oxide core of ferritin is poorly understood. A VO2+ spin probe study was undertaken to characterize the initial complex of Fe2+ with horse spleen apoferritin (96% L-subunits). A competitive binding study of VO2+ and Fe2+ showed that the two metals compete 1:1 for binding at the same site or region of the protein. Curve fitting of the binding data showed that the affinity of VO2+ for the protein was 15 times that of Fe2+. Electron nuclear double resonance (ENDOR) measurements on the VO(2+)-apoferritin complex showed couplings from two nitrogen nuclei, tentatively ascribed to the N1 and N3 nitrogens of the imidazole ligand of histidine. The possibility that the observed nitrogen couplings are from two different ligands is not precluded by the data, however. A pair of exchangeable proton lines with a coupling of approximately 1 MHz is tentatively assigned to the NH proton of the coordinated nitrogen. A 30-40% reduction in the intensity of the 1H matrix ENDOR line upon D2O-H2O exchange indicates that the metal-binding site is accessible to solvent and, therefore, to molecular oxygen as well. The ENDOR data provide the first evidence for a principle iron(II)-binding site with nitrogen coordination in an L-subunit ferritin. The site may be important in Fe2+ oxidation during the beginning stages of core formation.
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PMID:Iron binding to horse spleen apoferritin: a vanadyl ENDOR spin probe study. 165 90

The structure and crystal chemical properties of iron cores of reconstituted recombinant human ferritins and their site-directed variants have been studied by transmission electron microscopy and electron diffraction. The kinetics of Fe uptake have been compared spectrophotometrically. Recombinant L and H-chain ferritins, and recombinant H-chain variants incorporating modifications in the threefold (Asp131----His or Glu134----Ala) and fourfold (Leu169----Arg) channels, at the partially buried ferroxidase sites (Glu62,His65----Lys,Gly), a putative nucleation site on the inner surface (Glu61,Glu64,Glu67----Ala), and both the ferroxidase and nucleation sites (Glu62,His65----Lys,Gly and Glu61,Glu64,Glu67----Ala), were investigated. An additional H-chain variant, incorporating substitution of the last ten C-terminal residues for those of the L-chain protein, was also studied. Most of the proteins assimilated iron to give discrete electron-dense cores of the Fe(III) hydrated oxide, ferrihydrite (Fe2O3.nH2O). No differences were observed for variants modified in the three- or fourfold channels compared with the unmodified H-chain ferritin. The recombinant L-chain ferritin and H-chain variant depleted of the ferroxidase site, however, showed markedly reduced uptake kinetics and comprised cores of increased diameter and regularity. Depletion of the inner surface Glu residues, whilst maintaining the ferroxidase site, resulted in a partially reduced rate of Fe uptake and iron cores of wider particle size distribution. Modification of both ferroxidase and inner surface Glu residues resulted in complete inhibition of iron uptake and deposition. No cores were observed by electron microscopy although negative staining showed that the protein shell was intact. The general requirement of an appropriate spatial charge density across the cavity surface rather than specific amino acid residues could explain how, in spite of an almost complete lack of identity between the amino acid sequences of bacterioferritin and mammalian ferritins, ferrihydrite is deposited within the cavity of both proteins under similar reconstitution conditions.
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PMID:Influence of site-directed modifications on the formation of iron cores in ferritin. 194 61


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