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

Evidence is presented that French-bean (Phaseolus vulgaris) seed ferritin is composed of one type of subunit with an apparent Mr of 26500. In normal and iron-loaded leaf tissues it is detected immunologically with an antiserum raised against purified bean seed ferritin and migrates in SDS (sodium dodecyl sulphate)/polyacrylamide-gel electrophoresis with the same mobility as the bean seed ferritin subunit. The biosynthetic pathway of ferritin in normal and iron-loaded leaves was investigated. RNA was extracted, fractionated into polyadenylated RNA and translated in a cell-free rabbit reticulocyte lysate and a wheat-germ-extract system. The products were identified by SDS/polyacrylamide-gel electrophoresis after indirect immunoprecipitation. In all cases the ferritin product had an Mr 5000 higher than that of the native subunit. Uptake and processing of the precursor form of ferritin from iron-loaded leaves by intact chloroplasts was demonstrated. This indicates that, in iron-loaded leaves, ferritin acts as a chloroplast protein. We propose that the ferritin precursor in normal leaves follows the same biosynthetic pathway. This suggests that the iron-buffering function of ferritin in plants takes place in the chloroplast and that non-functional cellular iron will accumulate in this cell organelle.
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PMID:Phytoferritin is synthesized in vitro as a high-molecular-weight precursor. Studies on the synthesis and the uptake in vitro of the precursors of ferritin and ferredoxin by intact chloroplasts. 662 65

Ferritin was purified from rabbit livers either by heat treatment and immunoaffinity chromatography, or by immunoaffinity chromatography alone. The immunoreactivity of ferritin with antibodies raised against heat-treated ferritin was significantly higher for heat-treated preparations than for non-heated preparations. The amount of ferritin protein could be estimated with equal reliability by the assay according to Lowry et al. and by nitrogen determination. Heat treatment favoured the L-subunit-rich ferritin fraction, as measured by densitometric scanning of SDS gradient-pore polyacrylamide gels. Amino acid analysis showed small changes in the amounts of valine, isoleucine and histidine in the heat-treated ferritin, possibly due to selective partial degradation of H-subunit-rich forms of ferritin. These results illustrate that heat treatment, which is a commonly used step in most purification procedures, induces partial denaturation of the ferritin molecules.
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PMID:Influence of heat treatment on rabbit liver ferritin. 684 41

Cell surface receptor IgM molecules of cultured human lymlphoblastoid cells (WiL2) patch and redistribute into a cap over the Golgi region of the cell after treatment with multivalent anti-IgM antibodies. During and after the redistribution, ligand-receptor clusters are endocytosed into coated pits and coated vesicles. Morphometric analysis of the distribution of ferritin-labeled ligand at EM resolution reveals the following sequence of events in the endocytosis of cell surface IgM: (a) binding of the multivalent ligand in a diffuse cell surface distribution, (b) clustering of the ligand-receptor complexes, (c) recruitment of clathrin coats to the cytoplasmic surface of the cell membrane opposite ligand-receptor clusters, (d) assembly and (e) internalization of coated vesicles, and (f) delivery of label into a large vesicular compartment, presumably partly lysosomal. Most of the labeled ligand enters this pathway. The recruitment of clathrin coats to the membrane opposite ligand-receptor clusters is sensitive to the calmodulin-directed drug Stelazine (trifluoperazine dihydrochloride). In addition, Stelazine inhibits an alternate pathway of endocytosis that does not involve coated vesicle formation. The actin-directed drug dihydrocytochalasin B has no effect on the recruitment of clathrin to the ligand-receptor clusters and the formation of coated pits and little effect on the alternate pathway, but this drug does interfere with subsequent coated vesicle formation and it inhibits capping. Cortical microfilaments that decorate with heavy meromyosin with constant polarity are observed in association with the coated regions of the plasma membrane and with coated vesicles. SDS-polyacrylamide gel electrophoresis analysis of a coated vesicle preparation isolated from WiL2 cells demonstrates that the major polypeptides in the fraction are a 175-kdalton component that comigrates with calf brain clathrin, a 42-kdalton component that comigrates with rabbit muscle actin and a 18.5-kdalton minor component that comigrates with calmodulin as well as 110-, 70-, 55-, 36-, 30-, and 17-kdalton components. These results clarify the pathways of endocytosis in this cell and suggest functional roles for calmodulin, especially in the formation of clathrin-coated pits, and for actin microfilaments in coated vesicle formation and in capping.
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PMID:Role of coated vesicles, microfilaments, and calmodulin in receptor-mediated endocytosis by cultured B lymphoblastoid cells. 696 16

Antibodies to skeletal muscle actin were produced in rabbits and purified by affinity chromatography. Direct labeling of SDS-PAGE gels of whole cell homogenates from mouse fibroblast cells showed that actin was the only protein detected by these antibodies. Using this immunospecific reagent, we localized actin in cultured fibroblasts using the EGS fixation-permeabilization procedure with the ferritin bridge labeling technique. Swiss 3T3-4 mouse fibroblasts were chosen as an example of highly adherent untransformed cells with prominent microfilament bundles, and L929 mouse fibroblasts were chosen as an example of poorly adherent, rounded, transformed cells with prominent microvilli. Using these two cell types, we have characterized the intracellular distribution of action. Actin was only detected in locations in which morphologically recognizable 60 A microfilaments were found. By both fluorescence and electron microscopy, actin was found in surface ruffles, microvilli, microfilament bundles, the microfilament mat, and the leading lamellae of Swiss 3T3 and L929 cells. In addition, actin was found surrounding micropinosomes and macropinosomes. On the other hand, there was no actin detected around the base of coated pits. Morphometric quantitation showed that almost all the actin was localized in microfilamentous structures. Our results suggest that actin has an important role in cell motility and adhesion, and in the endocytosis of pinosomes, but that actin may not be involved in intracellular processes such as saltatory motion of intracellular organelles.
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PMID:Intracellular localization of actin in cultured fibroblasts by electron microscopic immunocytochemistry. 700 28

Plasma membranes of vertebrate lens fiber cells contain a major intrinsic polypeptide with an apparent molecular weight of 26,000 (MIP26). These plasma membranes are extremely rich in communicating junctions, and it has been suggested that MIP26 is a component of them. MIP26 was purified from cow lenses using preparative SDS gel electrophoresis followed by hydroxylapatite column chromatography. From gel electrophoresis patterns and aggregational properties it was concluded that the MIP26 preparation was homogeneous. The purified MIP26 was used to produce monospecific antibodies in rabbits as assessed by double immunodiffusion and crossed immunoelectrophoresis of purified MIP26 and solubilized lens plasma membranes against the antiserum. Indirect immunocytochemical studies were performed on open and closed lens plasma membrane vesicles by incubation in anti-MIP antiserum followed by ferritin-conjugated goat antirabbit IgG. The conjugate bound unequivocally to lens communicating junctions, indicating that MIP26 is a component of these structures.
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PMID:Immunocytochemical localization of the lens main intrinsic polypeptide (MIP26) in communicating junctions. 703 67

Treatment of rat liver rough microsomes (3.5 mg of protein/ml) with sublytical concentrations (0.08%) of the neutral detergent Triton X-100 caused a lateral displacement of bound ribosomes and the formation of ribosomal aggregates on the microsomal surface. At slightly higher detergent concentrations (0.12-0.16%) membrane areas bearing ribosomal aggregates invaginated into the microsomal lumen and separated from the rest of the membrane. Two distinct classes of vesicles could be isolated by density gradient centrifugation from microsomes treated with 0.16% Triton X-100: one with ribosomes bound to the inner membrane surfaces ("inverted rough" vesicles) and another with no ribosomes attached to the membranes. Analysis of the fractions showed that approximately 30% of the phospholipids and 20-30% of the total membrane protein were released from the membranes by this treatment. Labeling with avidin-ferritin conjugates demonstrated that concanavalin A binding sites, which in native rough microsomes are found in the luminal face of the membranes, were present on the outer surface of the inverted rough vesicles. Freeze-fracture electron microscopy showed that both fracture faces had similar concentrations of intramembrane particles. SDS PAGE analysis of the two vesicle subfractions demonstrated that, of all the integral microsomal membrane proteins, only ribophorins I and II were found exclusively in the inverted rough vesicles bearing ribosomes. These observations are consistent with the proposal that ribophorins are associated with the ribosomal binding sites characteristic of rough microsomal membranes.
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PMID:Recovery of ribophorins and ribosomes in "inverted rough" vesicles derived from rat liver rough microsomes. 706 49

Samples of graded, human lung cancer and of normal lung were assayed for total iron, ferritin, and ferritin iron saturation. Both kinds of tissues contained highly variable amounts of total and ferritin iron and had a range of ferritin iron:protein ratios. No quantitative correlations were found between cancer histopathology and these parameters, in contrast to previous findings for transplantable rat hepatomas. Examination of pooled ferritins isolated from normal lung and lung tumors by quantitative polyacrylamide gel electrophoresis, isoelectric focusing before and after acid-urea dissociation, and SDS electrophoresis, revealed no structural differences. It is concluded that at least for the human lung, malignancy of the kind examined causes no change in ferritin gene expression, and that ferritin assays would not be useful in the grading or detection of human lung cancer.
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PMID:Concentration, structure and iron saturation of ferritins from normal human lung and lung tumors with graded histopathology. 707 83

Anti 5-methyl-cytidine antibodies might be useful agents for the detection and localization of 5-methyl-cytidine of nucleic acids, but only if the antibodies recognize this nucleoside with sufficient specificity. A conjugate containing 18 moles of 5-methyl-cytidine per mole of BSA was prepared and antibodies directed against this nucleoside hapten were produced by immunization of rabbits (as determined by gel diffusion in agar containing excessive amounts of the carrier). A slight crossreaction of cytidine-BSA was eliminated by adsorption on the cross-reacting antigen. Further purification of the antibodies was effected by chromatography on DEAE-Sephadex A-50 and a method for the rapid quantitation of the antibodies showed that 12.7% of the IgG protein are monospecific against 5-methyl-cytidine-BSA. Hydrolysis of antibodies with insolubilized papain produced monovalent Fab fragments which were identified by SDS-Disk-electrophoresis. A two stage method for cross linking the immunoproteins to ferritin by glutaraldehyde was used. The isolation of immunoferritin conjugates by Bio-Gel A 1.5 m column chromatography is described. The identification of the effluents was made by glycerin density gradient ultracentrifugation. The results were visualized by electron microscopy after the treatment of immunoferritin conjugates with (methylated and unmethylated) denaturated DNA, fractionation on the glycerine density gradient, and the spreading by a modification of drop technique.
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PMID:Monospecific antibody against 5-methyl-cytidine for the structural analysis of nucleic acids. 711 47

We have modified a method for isolating gap-junctional membrane from mouse hearts [Kensler & Goodenough (1980) J. Cell Biol. 86, 755-764] to isolate gap junctions of comparable purity from rabbit hearts more rapidly, with better yield, and without resort to non-ionic detergents. Purification was monitored by electron microscopy of thin-sectioned membrane pellets and by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Gap junctions were obtained as vesicles whose mean surface area approximated that of junctions in intact myocardial cells. About 10-20% of the vesicles were ferritin-impermeable. Approx. 125 micrograms of membrane protein was obtained per 8 g of rabbit heart. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of purified gap junctions showed five major protein bands of mol.wts. 46 000, 44 000, 33 000, 30 000 and 28 500 that co-purified with the junctions. This protein composition was nearly identical with that published for gap junctions of mouse hearts, and differed markedly from the protein composition of gap junctions from non-excitable cells (lens and liver). The constancy of junctional protein composition between hearts of two different species and its non-identity with that from liver and lens suggest that, although gap-junctional structure in mammalian tissues seems to be remarkably similar by electron-microscopic techniques, junctional-channel protein composition actually varies from tissue to tissue and may be adapted to the permeability requirements of the tissue.
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PMID:Isolation and protein composition of gap junctions from rabbit hearts. 712 76

Correlated ultrastructural and biochemical methods were used to identify and localize Concanavalin A (Con A) receptors in the desmosomes of bovine epidermis. Specific carbohydrate residues were labeled with ferritin-Con A in thin sections of tissue embedded in a hydrophilic resin. Quantitative mapping of ferritin distribution in labeled desmosomes revealed that Con A receptors are localized in the intercellular zone and concentrated along the desmosomal midline or central dense stratum. Labeling was almost entirely absent when sections were treated with ferritin-Con A in the presence of 0.1 M alpha-methyl mannoside, a hapten-inhibitor of Con A. "Whole" desmosomes and desmosomal intercellular regions (desmosomal "cores") were purified from bovine muzzle epidermis. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis reveals a limited number of major desmosomal protein constituents. Certain of these are glycoproteins and are greatly enriched in the core fraction. Almost all the desmosomal glycoproteins are intensely labeled when electrophoretic gels of whole desmosome or core fractions are exposed to fluorescent Concanavalin A.
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PMID:Ultrastructural and biochemical identification of Con A receptors in the desmosome. 716 95


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