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

Ferritin was dissociated into subunits by various denaturants and the subunits were examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Human, horse, rat, and rabbit ferritins all exhibited characteristic patterns of heterogeneity; components with molecular weights of about 19,000, 11,000, and 8,000 were invariably found in these preparations. This result contradicts earlier reports that ferritin consists of 24 identical subunits. These polypeptides were isolated, purified in the presence of low concentrations of detergent, and characterized. Evidence based on amino acid compositions, NH2-terminal analysis and investigation of detergent-induced breakdown products, indicated that the 19,000 molecular weight component is a composite of the 8,000 and 11,000 molecular weight chains. Circular dichroism studies showed that the 19,000 molecular weight polypeptide retained appreciable amounts of ordered secondary structure whereas the two lower molecular weight peptides were unfolded to a much greater extent. If the 8,000 and 11,000 molecular weight polypeptides were recombined in equimolar amounts and the denaturant was completely removed, a substance with electrophoretic mobility and morphological appearance of native apoferritin was obtained.
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PMID:Characterization of the different polypeptide components and analysis of subunit assembly in ferritin. 23 40

A method is described for indirect electron microscopic visualization and mapping of tRNA and other short transcripts hybridized to DNA. This method depends upon the attachment of the electron-dense protein ferritin to the RNA, the binding being mediated by the remarkably strong association of the egg white protein avidin with biotin. Biotin is covalently attached to the 3' end of tRNA using an NH2(CH2)5NH2 bridge. The tRNA-biotin adduct is hybridized to complementary DNA sequences present in a single stranded non-homology loop of a DNA:DNA heteroduplex. Avidin, covalently crosslinked to ferritin, is mixed with the heteroduplex and becomes bound to the hybridized tRNA-biotin. Observation of the DNA:RNA-biotin:avidin-ferritin complex by electron microscopy specifically and accurately reveals the position of the tRNA gene, with a frequency of labeling of approximately 50%.
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PMID:Electron microscopic visualization of tRNA genes with ferritin-avidin: biotin labels. 34 43

The iron-responsive element binding protein (IRE-BP) is a cytosolic protein that binds a highly conserved sequence in the untranslated regions of mRNAs involved in iron metabolism including ferritin, transferrin receptor, and erythroid 5-aminolevulinate acid synthase. This conserved sequence is termed the iron-responsive element and is necessary for the post-transcriptional regulation of these mRNAs by iron. The rat liver IRE-BP was purified to homogeneity by chromatographic methods and partial amino acid sequence was obtained. A cDNA was isolated from a rat liver cDNA library and sequenced. The amino acid sequence deduced from the cDNA sequence corresponds to a protein of 889 amino acids with a predicted molecular weight of 97.946. The NH2-terminal sequence obtained by Edman degradation matched the deduced amino acid sequence obtained from the cDNA, confirming the translational start site. Rat liver IRE-BP shares 95% identity with human IRE-BP and 98% identity with mouse IRE-BP indicating that the IRE-BPs have remained highly conserved during evolution. The 5'-untranslated region is at least 236 nucleotides and contains interesting structural features including two direct repeats, an inverted repeat, and three small open reading frames. The rat IRE-BP mRNA is approximately 3600 nucleotides and is expressed in a variety of rat tissues including liver, spleen, and gut. Over the course of 16 h following an intraperitoneal injection of iron in rats. IRE-BP RNA binding activity decreases to 50% of control levels. The decrease in IRE-BP RNA binding activity in extracts from iron-treated rats is reversible by pretreatment of the extracts with reducing agents. The steady-state levels of IRE-BP mRNA remain constant during iron treatment. These data suggest that the decrease in IRE-BP RNA binding activity by iron in rat liver is due to post-translational changes in the RNA binding affinity of the IRE-BP and not due a decrease in the transcription of the IRE-BP gene or to the destabilization of the IRE-BP mRNA.
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PMID:The iron-responsive element binding protein. Purification, cloning, and regulation in rat liver. 152 27

The iron-storage protein ferritin has been purified to homogeneity from maize seeds, allowing to determine the sequence of the first 29 NH2-terminal amino acids of its subunit and to raise specific rabbit polyclonal antibodies. Addition of 500 microM Fe-EDTA/75 microM Fe-citrate to hydroponic culture solutions of maize plantlets, previously starved for iron, led to a significant increase of the iron concentration of roots and leaves, albeit root iron was mainly found associated with the apoplast. Immunodetection of ferritin by western blots indicated that this iron treatment induced ferritin protein accumulation in roots and leaves over a period of 3 days. In order to investigate this induction at the ferritin mRNA level, various ferritin cDNA clones were isolated from a cDNA library prepared from poly(A)+ mRNA isolated from roots 48 h after iron treatment. These cDNAs were classified into two groups called FM1 and FM2. Upstream of the sequence encoding the mature ferritin subunit, both of these cDNAs contained an in-frame coding sequence with the characteristics of a transit peptide for plastid targeting. Two members of the FM1 subfamily, both partial at their 5' extremity, were characterized. They are identical, except in their 3' untranslated region: FM1A extends 162 nucleotides beyond the 3' terminus of FM1B. These two mRNAs could arise from the use of two different polyadenylation signals. FM2 is 96% identical to FM1 and contains 45 nucleotides of 5' untranslated region. Northern analyses of root and leaf RNAs, at different times after iron treatment, revealed ferritin mRNA accumulation in response to iron. Ferritin mRNA accumulation was transient and particularly abundant in leaves, reaching a maximum at 24 h. The level of ferritin mRNA in roots was affected to a lesser extent than in leaves.
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PMID:Iron induces ferritin synthesis in maize plantlets. 162 71

Iron regulatory factor (IRF), also called iron responsive element-binding protein (IRE-BP), is a cytoplasmic RNA-binding protein which regulates post-transcriptionally transferrin receptor mRNA stability and ferritin mRNA translation. By using the polymerase chain reaction (PCR) and the sequence published by Rouault et al. (1990) a probe was derived which permitted the isolation of three human IRF cDNA clones. Hybridization to genomic DNA and mRNA, as well as sequencing data indicated a single copy gene of about 40 kb specifying a 4.0 kb mRNA that translates into a protein of 98,400 dalton. By in vitro transcription of a assembled IRF cDNA coupled to in vitro translation in a wheat germ extract, we obtained full sized IRF that bound specifically to a human ferritin IRE. In vitro translated IRF retained sensitivity to sulfhydryl oxidation by diamide and could be reactivated by beta-mercaptoethanol in the same way as native placental IRF. An IRF deletion mutant shortened by 132 amino acids at the COOH-terminus was no longer able to bind to an IRE, indicating that this region of the protein plays a role in RNA recognition. Placental IRF has previously been shown to migrate as a doublet on SDS-polyacrylamide gels. After V8 protease digestion the heterogeneity was located in a 65/70 kDa NH2-terminal doublet. The liberated 31 kDa COOH-terminal polypeptide was found to be homogeneous by amino acid sequencing supporting the conclusion of a single IRF gene.
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PMID:Expression of active iron regulatory factor from a full-length human cDNA by in vitro transcription/translation. 173 1

Bovine heart microsomes have been found to contain a non-heme iron protein which serves as an electron acceptor for NADPH-cytochrome P-450 reductase and therefore stimulates NADPH oxidation. This protein, tentatively referred to as Microsomal Iron Protein (MIP), has been extracted with Triton N-101 and purified by ion exchange chromatography on CM- and DEAE-celluloses and gel filtration on Sepharose 6B. MIP is an Mr = 66,000 monomer with 17 atoms of Fe(III)/molecule. Incubation with dithionite removes iron from MIP and abolishes the stimulation of NADPH oxidation, but subsequent incubation with nitrilotriacetic-Fe(III) reincorporates iron and restores the stimulation of NADPH oxidation. Oxygen is the ultimate electron acceptor. In the presence of oxygen, the enzymatic reduction of MIP Fe(III) is followed by the reoxidation of Fe(II) at the expense of oxygen, generating superoxide anion and regenerating MIP Fe(III) for the continuous oxidation of NADPH. In the absence of oxygen, electron transfer from the reductase to MIP Fe(III) causes the release of Fe(II), which limits the ability of MIP to serve as an electron acceptor and stimulate NADPH oxidation. The--NH2-terminal of MIP has been sequenced, and no homology has been found with the sequence of other iron storage or transport proteins such as ferritin or transferrin.
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PMID:Bovine heart microsomes contain an Mr = 66,000 non-heme iron protein which stimulates NADPH oxidation. 193 64

The possibility of improving analytical parameters of the immunometric assay with the use of biotinylated antibodies and biotin-streptavidin complexes in comparison with the commonly known approach of direct antibody modification with 125I has been studied. Experiments have been carried out with the use of low-affinity antibodies (Kass approximately 10(9) M-1) to ferritin. The signal-to-noise ratio in the immunometric increases 2.3 times when streptavidin labeled with horse-radish peroxidase is used and 4.3 times when the preformed streptavidin + biotin-peroxidase complex is used in comparison with assay systems based on 125I-labeled antibodies. The improvement of assay parameters of immunochemical systems by means of biotin-streptavidin complexes has been found to permit the use of low-affinity antibodies as assay reagents, thus ensuring analytical parameters attaining or close to those of immunoradiometric assay systems based on high-affinity 125I-labeled antibodies (Kass approximately 10(10) M-1). As shown in this study, the following factors ensure the signal enhancement in biotin-streptoavidin systems: (a) the biotin modification of several lysin residues per IgG molecule, the optimum extent of modification being 3-4 residues per molecule; (b) mild procedure for biotinylation. In contrast to oxidative iodination, the modification of NH2 groups with biotin esters does not significantly affect their antigen-binding properties.
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PMID:[The use of biotin-streptavidin systems for enhancing the parameters of immunometric analysis]. 207 57

Ferritin is a large multisubunit protein that stores iron in plants, animals, and bacteria. In animals, the protein is mainly cytoplasmic and is highly conserved, while in plants ferritin is found in chloroplasts and other plastids. Ferritin is synthesized in plants as a larger precursor of the mature subunit. There is no sequence information for ferritin from plants, except an NH2-terminal peptide of 35 residues which shows little similarity to any known ferritin sequences or transit peptides (Laulhere, J. P., Laboure, A. M., and Briat, J. F. (1989) J. Biol. Chem. 264, 3629-3635). To understand the genetic origin and the location of ferritin synthesis in plant cells, as well as the structure of ferritin from plants, we have sequenced both CNBr peptides from pea seed ferritin and nucleotides of a soybean hypocotyl ferritin cDNA, identified using a frog ferritin cDNA as a probe. Comparison of pea and soybean sequences showed an identity of 89%. Alignment of the plant ferritin sequences with animal ferritins showed 55-65% sequence identity in the common regions. However, a peptide of 28 amino acids extended the NH2 terminus of the plant ferritins. Furthermore, the cDNA encoded additional amino acids which appear to be a transit peptide. None of the sequences in soybean ferritin were found in the tobacco chloroplast genome, suggesting, as does the transit peptide, a nuclear location of ferritin gene(s) in plants. Plant ferritin mRNA is 400-500 nucleotides longer than animal ferritin mRNAs, a difference accounted for in part by the extra peptides encoded. The size of soybean ferritin mRNA was constant in different tissues but expression varied in different tissues (leaf greater than hypocotyl). Thus, higher plants and animal ferritins display sequence homology and differential tissue expression. An ancient, common progenitor apparently gave rise to contemporary eukaryotic ferritins after specific modifications, e.g. transport to plasmids.
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PMID:Evidence for conservation of ferritin sequences among plants and animals and for a transit peptide in soybean. 221 6

The effect of prolonged exposure to ammonia on fluid-phase, receptor-mediated, and adsorptive (non specific) endocytosis in cultured neuroblastoma (Neuro-2a) cells were studied using fluorescein-labeled dextran, concanavalin A conjugated with fluorescein isothiocyanate, and cationized ferritin as tracers. Ammonia treatment increased the rate of endocytosis of cationized ferritin as well as the number of cell elements involved in the process. Moreover, the number of cytoplasmic components containing acid phosphatase activity was also found to increase following ammonia treatment. In contrast, flow-cytometric analyses showed that, under experimental conditions, exposure to ammonia did not alter the intralysosomal pH and had little effect on the fluid-phase and receptor-mediated endocytosis of fluorescein-labeled dextran and concanavalin-A fluorocrome, respectively.
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PMID:Effects of prolonged exposure to ammonia on fluid-phase, receptor-mediated, and adsorptive (non specific) endocytosis in cultured neuroblastoma cells. A flow-cytometry and cytochemical study. 244 72

Soluble and insoluble forms of ferritins have been purified from dry pea seeds by gel filtration. The insoluble form is called phytosiderin by analogy with animal hemosiderin. Native gel electrophoresis of these two forms have shown that the soluble one (ferritin) is homogenous in size and more compact than the insoluble one (phytosiderin) which is heterogenous in size. However, when iron is removed from these two classes of molecules (apoferritin), they have the same mobility in isopycnic centrifugations. Polyacrylamide-sodium dodecyl sulfate gel electrophoresis revealed a difference in their subunit composition: ferritin molecules are built up from a 28-kDa subunit and phytosiderin from a 26.5-kDa subunit. Partial proteolysis using a Staphylococcus aureus protease indicates a strong relationship between these two polypeptides. Intermediates between these two forms have also been characterized and are composed of both subunits in various amounts. Ferritin and phytosiderin are both able to incorporate iron in vitro into their mineral core. It is also shown that in vitro iron exchange induces ferritin degradation. This degradation is prevented by inhibitors of the Fenton cycle (iron chelates like o-phenanthroline and desferrioxamine B) and reduced by Tris, a radical scavenger. Under in vitro conditions of controlled radical damage the 28-kDa subunit is converted into the 26.5-kDa subunit. Purification of the 28-kDa subunit has allowed us to determine the NH2-terminal sequence. The NH2 extremity of the 26.5-kDa subunit is heterogenous, but the sequence of its main component is identical to the sequence of the 28-kDa subunit downstream residue Leu-21. These data indicate that the 26.5-kDa subunit is produced by radical mediated damage leading to a series of cleavages in the NH2 terminal part of the 28-kDa subunit.
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PMID:Mechanism of the transition from plant ferritin to phytosiderin. 253 54


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