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

The intestinal epithelium of Ascaris suum consists of a single layer of tall columnar epithelial cells that rest on a thick basal membrane in contact with the pseudocoelomic cavity. Experiments were conducted on glutaraldehyde-fixed tissue to ascertain the nature of the electronegative charges associated with both the apical microvillar surface and basal membrane. A strong electronegative charge was demonstrated on the microvillar surface and basal membrane with ruthenium red and cationic ferritin staining. The ionic nature of ferritin binding was demonstrated with poly-L-lysine, a polycation that interacts with anionic groups on the membrane and thus blocks the subsequent binding of ferritin. Tissue thus treated was devoid of reaction product. Methylation with diazomethane completely abolished staining. Since the stronger acidic groups of sulfates or phosphates would not be protonated under the conditions employed in this study, and therefore susceptible to methylation, staining by ferritin is thought to be due to its interaction with carboxyl groups. Prior enzymatic treatment of tissue with neuraminidase or phospholipase C had no effect on subsequent ferritin binding. Tissue exposed to colloidal iron at various pH values showed maximal reactivity at a pH of 2.5 or above. Above pH 2.5, the dissociation of protons from free carboxyl groups of protein-bound amino-acid residues with pK's of 3.8 and 4.2 would be maximal, and the ionized carboxyl groups are then available to interact with iron micelles. These results suggest the presence of weaker acidic groups, such as the carboxyl groups of acidic amino acids or uronic acid residues. The stronger acidic groups of sialic acid and the esterified sulfate groups, if present, contribute only minimally to overall staining. These results demonstrate that a high electronegative charge density exists, despite the apparent lack of sialic acid. Staining is believed to be due to carboxyl groups of acidic amino acids and/or carboxyl groups or uronic acid residues.
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PMID:Ultrastructural observations on the cell surface of the intestinal epithelium of the nematode, Ascaris suum. Nature of the electronegative charge. 615 29

Glomerular development was studied in the newborn rat kidney by electron microscopy and cytochemistry. Glomerular structure at different developmental stages was related to the permeability properties of its components and to the differentiation of anionic sites in the glomerular basement membrane (GBM) and on endothelial and epithelia cell surfaces. Cationic probes (cationized ferritin, ruthenium red, colloidal iron) were used to determine the time of appearance and distribution of anionic sites, and digestion with specific enzymes (neuraminidase, heparinase, chondroitinases, hyaluronidases) was used to determine their nature. Native (anionic) ferritin was used to investigate glomerular permeability. The main findings were: (a) The first endothelial fenestrae (which appear before the GBM is fully assembled) possess transient, negatively charged diaphragms that bind cationized ferritin and are impermeable to native ferritin. (b). Two types of glycosaminoglycan particles can be identified by staining with ruthenium red. Large (30-nm) granules are seen only in the cleft of the S-shaped body at the time of mesenchymal migration into the renal vesicle. They consist of hyaluronic acid and possibly also chondroitin sulfate. Smaller (10-15-nm) particles are seen in the earliest endothelial and epithelial basement membranes (S-shaped body stage), become concentrated in the laminae rarae after fusion of these two membranes to form the GBM, and contain heparan sulfate. They are assumed to be precursors of the heparan sulfate-rich granules present in the mature GBM. (c) Distinctive sialic acid-rich, and sialic acid-poor plasmalemmal domains have been delineated on both the epithelial and endothelial cell surfaces. (d) The appearance of sialoglycoproteins on the epithelial cell surface concides with the development of foot processes and filtration slits. (e) Initially the GBM is loosely organized and quite permeable to native ferritin ;it becomes increasinly impermeable to ferritin as the lamina densa becomes more compact. (f) The number of endothelial fenestrae and open epithelial slits increases as the GBM matures and becomes organized into an effective barrier to the passage of native ferritin.
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PMID:Assembly of the glomerular filtration surface. Differentiation of anionic sites in glomerular capillaries of newborn rat kidney. 615 76

The biological and antigenic roles of glycosylation were investigated in the influenza hemagglutinin (HA) glycoprotein using the glycosylation inhibitor tunicamycin (TM). Under conditions where only the nonglycosylated form of HA was detected by immunoprecipitation and gel electrophoresis, the migration of glycoproteins to the cell surface was observed by immunofluorescence using either monospecific or monoclonal antibody to the HA polypeptide. Analysis of the surface fluorescence in TM-treated infected cells by a fluorescence-activated cell sorter (FACS) showed that all cells exhibited fluorescence in the complete absence of glycosylation. The relative amount of HA antigen on cell surfaces was found to be reduced by only 30-40% in TM-treated cells, and this reflected a similar reduction in intracellular synthesis. Electron microscopic studies using ferritin labeling also demonstrated that the nonglycosylated HA glycoprotein was present in significant amounts on surfaces of infected cells. Virions with nonglycosylated glycoproteins were purified, and were found to have an approximate 30-fold decrease in both hemagglutinin and neuraminidase specific activities. The possible role of oligosaccharides in antigenic variation among various H1N1 strains was investigated. Immunoprecipitation reactions involving five different monoclonal antibodies and five antigenic variants of A/USSR/90/77 revealed no major antigenic differences between the glycosylated and nonglycosylated forms of HA.
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PMID:Studies on the role of glycosylation in the functions and antigenic properties of influenza virus glycoproteins. 619 89

Scanning electron microscopy (SEM) of mouse cornea and conjunctiva fixed with picric acid-paraformaldehyde-glutaraldehyde (PA-P-G) mixture revealed a thin layer of amorphous material covering the microvilli of the corneal surface cells. At the transmission electron microscopic (TEM) level, this layer of material stained positively with dialyzed iron, alcian blue and cationized ferritin, all of which are markers for anionic sulfate or carboxyl groups. The corneal surface was negative for high iron diamine, which specifically stains sulfate groups. These results indicate that the murine ocular surface is rich in carboxyl groups. Treatment with neuraminidase prior to fixation significantly reduced (P less than 0.005) cationic ferritin binding, suggesting that most of the carboxyl groups at the ocular surface are associated with sialic acid residues. The corneal surface also stained positively at the TEM level when a periodic acid-thiocarbohydrazide-silver protein sequence (PA-T-SP) was applied. This result indicated the presence of periodic acid-Schiff (PAS)-positive glycoprotein and glycolipid at the ocular surface.
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PMID:Complex carbohydrates at the ocular surface of the mouse: an ultrastructural and cytochemical analysis. 620 40

Homogenates of central myelin were treated with ferritin derivatives having different isoelectric points. It was found that considerable amounts of cationic ferritin (pI 8.5-9.5) had access to the extracellular space, but that anionic ferritin (pI 4.0) and native ferritin (pI 4.5) did not. The electrostatic nature of the binding of cationic ferritin was demonstrated by treating the homogenates with poly-L-lysine and 1 M NaCl:both reagents led to a complete displacement of the bound cationic ferritin. Neither extensive trypsination nor neuraminidase treatment showed a significant effect on the intralamellar distribution of the bound cationic ferritin molecules. This suggests that the net negative charge on the extracellular myelin face stems primarily from acidic lipid groups in the membrane.
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PMID:Cytochemical demonstration of negative surface charges in central myelin. 630 34

Chrysotile asbestos interacts with mucin-secreting cells of tracheal organ cultures, causing an increase in secretion of mucin into the culture medium. This response occurs in the absence of obvious morphologic damage to tracheal epithelial cells. We speculated that asbestos-induced hypersecretion was regulated by the interaction of fibers with specific carbohydrate residues on the cell surface. To test this hypothesis, lectins, i.e., proteins with a high affinity for mono- and oligosaccharides on the plasma membrane, were added to tissues 30 min before addition of chrysotile. Secretion of mucin into the medium was then determined over a 2-hr period by using incorporation of 3H-glucosamine. Blocking of alpha-D-mannose and alpha-D-glucose residues inhibited chrysotile-induced hypersecretion (p less than 0.05), whereas lectins blocking residues of alpha-D-N-acetylgalactosamine, beta-D-N-acetylglucosamine, alpha-L-fucose and sialic acids were ineffective. Preincubation of cultures with carboxypeptidase A or phospholipase A2, but not with neuraminidase, diminished mucin secretion caused by chrysotile. To determine if the positive surface charge of chrysotile was important in interaction with mucin cells, we examined comparatively the effects of various polycations (cationic ferritin, polylysine, DEAE-dextran) and chrysotile after leaching of fibers to remove Mg2+. Although use of polycations enhanced secretion of mucin, effects were not as striking as those observed with chrysotile. In contrast, leached chrysotile failed to elicit a hypersecretory response. These results suggest the interaction of a positively charged component (presumably Mg2+) of chrysotile with glycolipids and glycoproteins containing terminal residues of alpha-D-mannose or alpha-D-glucose.
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PMID:Studies using lectins to determine mineral interactions with cellular membranes. 631 63

Anionic sites on the surface of cultured pigment epithelium cells from normal and dystrophic rats were studied. Cytochemical procedures and quantitative analysis were employed in order to determine distribution patterns and labeling densities. Anionic sites, in general, were localized with cationized ferritin at pH 7.0. The presence and density of sialic acid residues on the pigment epithelium cell surface were evaluated with colloidal iron at pH 1.8. Dystrophic cells contained 20% more cationized ferritin-binding sites as compared with normal pigment epithelium cells. With colloidal iron, an 18% increase in labeling density was measured in dystrophic pigment epithelium cells. Pretreatment with neuraminidase reduced subsequent labeling with colloidal iron by 93-97%. Thus, the presence of sialic acid residues on the surface of pigment epithelium cells and a significant increase in its content on the surface of dystrophic cells were established.
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PMID:Cytochemical evaluation of anionic sites on the surface of cultured pigment epithelium cells from normal and dystrophic RCS rats. 631 68

Immunochemical and immunocytochemical techniques have been used to characterize viral glycoproteins and endogenous rat leukaemia viruses (RaLV) produced both by Novikoff hepatocellular carcinoma cells and spontaneously transformed Wistar rat embryo cells (WRC). Results from immunocytochemical analysis demonstrated that RaLV produced by Novikoff and WRC cells could be distinguished by their unique patterns of reactivity with xenoantisera raised against virus particles or viral glycoproteins. This differential labelling was unexpected since all the antisera tested had been shown by immunoprecipitation and immunodepletion analysis to be reactive with viral glycoproteins expressed on the cell surface. Since no significant differences in cell surface-associated viral glycoproteins and those shed from the cell surface were detected by pulse iodination analysis, it was concluded that the apparent discrepancy between immunoferritin labelling and immunoprecipitation analysis resulted from differences in antigen accessibility on intact virions caused by structural differences in the viral glycoproteins expressed on Novikoff and WRC cells. This conclusion was supported by results from ferritin-lectin labelling, affinity chromatography and neuraminidase digestion studies which demonstrated differences in the saccharide moieties on both virion and cell surface-associated viral glycoproteins. Further evidence of structural differences was provided by limited digestion with trypsin and V8 protease of the Mr 64 000 (Nov gp64) and Mr 68 000 (WRC gp68) viral glycoproteins immunoprecipitated from Novikoff and WRC cells, respectively, with either monospecific anti-Rauscher murine leukaemia virus anti-gp70 serum or monospecific antiserum against Nov gp64 (anti-gp64). Results from digestion studies showed that all the major cleavage fragments from WRC gp68 were of higher molecular weight than their Nov gp64-derived counterparts. Evidence that Nov gp64 and WRC gp68 both share structural homology with other murine viral gp70s was suggested by results from immunoprecipitation analysis with anti-gp70 and anti-gp64 sera under reducing and non-reducing conditions which demonstrated the presence of an interchain disulphide bond in both glycoproteins and showed that at least some of these molecules exist on the cell surface as disulphide-linked heterodimers of Mr 78 000 and 82 000.
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PMID:Structural differences in envelope glycoproteins associated with rat leukaemia virus produced by Novikoff hepatocellular carcinoma and spontaneously transformed Wistar rat embryo cells. 636 46

The surface of rat arterial smooth muscle cells was characterized with respect to some of its chemical and functional properties. The effects of selective enzymic degradations (hyaluronidase, chondroitinases, heparitinase or neuraminidase) on [35S]sulphate-prelabelled cells and on binding sites for cationized ferritin (CF) were examined to assess the presence and relative importance of individual species of macromolecules on the cell surface. The results indicate that about half of the strongly anionic sites on the cell surface (binding CF at pH 2.0) could be ascribed to sulphate groups of glycosaminoglycans and about half to carboxyl groups of sialic acid residues in glycoproteins and/or glycolipids. Weaker anionic sites (binding CF at pH 7.0) largely originated from carboxyl groups of glycosaminoglycans. Chondroitin sulphate and heparan sulphate were the main glycosaminoglycans. The surface of cells from young animals showed a higher glycosaminoglycan and a lower sialic acid content than that of cells from adult animals. Continuous treatment of the cultures with neuraminidase stimulated serum-induced initiation of DNA synthesis, while treatment with hyaluronidase or heparitinase inhibited it. Addition of hyaluronic acid, heparin or heparan sulphate to the culture medium inhibited initiation of DNA synthesis as well as cell proliferation. The effect was more marked in cultures of cells from young animals than from adults, although the latter cells were found to grow at a higher rate and to higher densities. These results suggest a role for cell-surface and pericellular glycoconjugates in growth regulation. A possible mechanism of action is that these molecules, due to their anionic charge or by steric exclusion, interfere with the binding of platelet-derived growth factor, a highly cationic polypeptide, to its cell-surface receptor.
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PMID:Cell surface components and growth regulation in cultivated arterial smooth muscle cells. 642 Apr 21

To investigate the chemical nature of the cationic ferritin (CF)-binding sites of the differentiated microdomains of the capillary endothelium, the vasculature of the mouse pancreas and intestinal mucosa was perfused in situ with neuraminidase, hyaluronidase, chondroitinase ABC, heparinase, and three proteases: trypsin, papain, and pronase. Proteases of broad specificity removed all anionic sites, suggesting that the latter are contributed by acid glycoproteins or proteoglycans. Neuraminidase, hyaluronidase, and chondroitinase ABC reduced the density of CF-binding sites on the plasmalemma proper, but had no effect on either coated pits or fenestral diaphragms. Heparinase removed CF-binding sites from fenestral diaphragms and had no effect on coated pits. Taken together, these results indicate that the anionic sites of the fenestral diaphragms are contributed primarily by heparan sulfate and/or heparin, whereas those of the plasmalemma proper are of mixed chemical nature. The membranes and diaphragms of plasmalemmal vesicles and transendothelial channels do not bind CF in control specimens; this condition is not affected by the enzymic treatments mentioned above.
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PMID:Differentiated microdomains on the luminal surface of the capillary endothelium. II. Partial characterization of their anionic sites. 645 53


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