Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The distribution of (Na+ + K+) ATPase over the plasma membranes of the proximal convoluted tubule from canine renal cortex has been determined. Ultrathin frozen sections of this tissue were stained with rabbit antibodies to this enzyme and ferritin-conjugated goat antirabbit gamma-globulin. It is demonstrated that high concentrations of this enzyme uniformly line the intercellular spaces of this epithelium. The consequences of this observation are discussed in terms of the low resistant tight junctions of these tubules and the isotonic fluid transport which they support. Furthermore, antibodies to (Na+ + K+) ATPase recognize an antigen on the luminal surfaces of the tubules within the brush border. It is proposed that the enzyme is present in this region of the plasma membrane as well, although at much lower concentration. To further substantiate this conclusion, a brush border fraction has been purified from rabbit kidney and been shown to contain significant (Na+ + K+) ATPase. These results contradict earlier conclusions about the location of (Na+ + K+) ATPase in this tissue.
 ...
PMID:Immunoferritin determination of the distribution of (Na+ + K+) ATPase over the plasma membranes of renal convoluted tubules. II. Proximal segment. 12 58

The major protein associated with actin in the microfilament core of intestinal microvilli has been purified. This protein, for which we propose the name villin, has a polypeptide molecular weight of approximately 95,000. Two arguments suggest that villin may be the microvillus crossfilament protein that links the microfilament core laterally down its length to the cytoplasmic side of the plasma membrane. First, electron microscopy shows that crossfilaments stay attached to isolated membrane-free microvillus cores. Calculation of the expected abundance of the crossfilament protein shows that only villin is present in sufficient quantity to account for these structures. Second, decoration of microvillus cores by antibodies to either actin or villin, followed by ferritin-labeled second antibody in a sandwich procedure, results in specific labeling of the cores in both cases. The antivillin decoration, however, gives rise to a greater increase in diameter, in agreement with a model in which villin projects from the F-actin microfilament core. Villin is distinct from alpha-actinin, a protein suggested to be involved in membrane anchorage of microfilaments in nonmuscle cells. The two proteins differ in molecular weight. Specific antibodies against villin and alpha-actinin show no immunological crossreactivity. Immunofluorescence microscopy reveals that villin is located in the microvilli of the brush border whereas alpha-actinin is absent from the microvilli but is found in the terminal web. In addition, villin is not found in microfilament bundles of tissue culture cells, which are rich in alpha-actinin. Thus, villin and alpha-actinin appear to be immunologically and functionally different proteins.
 ...
PMID:Villin: the major microfilament-associated protein of the intestinal microvillus. 28 75

alpha-Actinin was localized in chicken intestinal epithelial cells by immunofluorescence and immunoferritin labeling of thin frozen sections. Most of the label of the brush border was confined to the terminal web area. The label there was concentrated mainly along the "roots" of the microvilli core microfilaments and in the vicinity of the zonula adherens. In the latter structure, the narrow electron-dense zones adjacent to the cell membranes, however, were not significantly labeled. This suggests that alpha-actinin does not mediate directly the association of the transverse terminal web microfilaments to the membrane at the zonula adherens. Sparse ferritin labeling was found near the tight junction, whereas the staining associated with the spot desmosome was negligible. The microvilli were not significantly labeled by either immunofluorescence or immunoferritin staining unless the sections were previously treated with detergent. Moreover, alpha-actinin (or a structurally related protein) was not detected in preparations of purified microvillar vesicles, suggesting the possibility that the alpha-actinin staining in the microvilli may be an artificial due to its translocation by the detergent from the terminal web onto the microvilli. The possible roles of alpha-actinin in the organization and function of the brush border are discussed.
 ...
PMID:Immunocytochemical localization of alpha-actinin in intestinal epithelial cells. 37 65

Immunoelectron microscopy was used to localize the brush border hydrolases sucrase-isomaltase (SI) and dipeptidylpeptidase IV (DPPIV) in the human colon carcinoma cell line Caco-2. Both enzymes were detected at the microvillar membrane, in small vesicles and multivesicular bodies (MVBs), and in lysosomal bodies. In addition, DPPIV was found in the Golgi apparatus, a variety of apical vesicles and tubules, and at the basolateral membrane. To investigate whether the hydrolases present in the lysosomal bodies were endocytosed from the apical membrane, endocytic compartments were marked with the endocytic tracer cationized ferritin (CF). After internalization from the apical membrane through coated pits, CF was first recovered in apical vesicles and tubules, and larger electronlucent vesicles (early endosomes), and later accumulated in MVBs (late endosomes) and lysosomal bodies. DPPIV was localized in a subpopulation of both early and late endocytic vesicles, which contained CF after 3 and 15 min of uptake, respectively. Also, internalization of the specific antibody against DPPIV and gold labeling on cryosections showed endocytosed DPPIV in both early and late endosomes. However, unlike CF, no accumulation of DPPIV was seen in MVBs or lysosomal bodies after longer chase times. The results indicate that in Caco-2 cells the majority of brush border hydrolases present in lysosomal bodies are not endocytosed from the brush border membrane. Furthermore, the labeling patterns obtained, suggest that late endosomes may be involved in the recycling of endocytosed DPPIV to the microvilli.
 ...
PMID:Intracellular localization and endocytosis of brush border enzymes in the enterocyte-like cell line Caco-2. 167 71

The binding of Phaseolus vulgaris (PHA) isolectins L4 and E4 to the brush border membrane of differentiated Caco-2 cells was studied and the impact on cellular metabolism and microvilli was assessed. Computer analysis of the data based on binding experiments with peroxidase conjugated isolectins gave mean (SD) values for maximal binding of 2540 (151).10(-9) M for PHA-L4 and 2104 (140).10(-9) M for PHA-E4 per mg of brush border membrane protein. The dissociation constants for L4 and E4 binding were 4.3 (1.4).10(-6) M and 1.1 (0.8).10(-6) M, respectively. Incubation of differentiated Caco-2 cells for 30 minutes with ferritin conjugated PHA isolectins showed that, as indicated by the number of ferritin particles, PHA-E4 bound to the microvilli to a greater extent than PHA-L4. Ferritin particles were also localised intracellularly over endocytotic invaginations and vesicles. After incubation for 48 hours with PHA-L4 or PHA-E4, the relative incorporation of precursors for DNA, RNA, and (glyco)protein synthesis into the trichloroacetic acid insoluble fraction of the Caco-2 cells was determined. Both isolectins stimulated the incorporation of thymidine and glucosamine, but neither PHA-L4 nor PHA-E4 were able to influence the incorporation of uridine. With respect to fucose, methionine, and N-acetyl mannosamine, the stimulatory effect remained confined to PHA-E4. Since PHA-L4 and PHA-E4 were tested at the same concentrations, PHA-E4 is more effective than PHA-L4. The changes in the uptake of radioactive precursors were lost after heat inactivation of PHA-E4. Compared with control and PHA-L4 incubated Caco-2 cells, the microvilli of PHA-E4 incubated cells were shortened significantly (p less than 0.01).
 ...
PMID:Binding of kidney bean (Phaseolus vulgaris) isolectins to differentiated human colon carcinoma Caco-2 cells and their effect on cellular metabolism. 186 41

Lactoferrin is an iron binding glycoprotein which is abundantly present in human tear fluid. It is also present in other secretions and in the specific granules of the polymorphonuclear leucocyte. The main biological properties of lactoferrin can be ascribed to its very strong binding of iron cations. Receptors for lactoferrin have been found in the intestinal brush border, suggesting that it may play a role in iron absorption from the gut. Macrophages also have a receptor for lactoferrin, which are possibly involved in the transfer of iron to ferritin. More important may be the fact that deprivation of iron from the gut or from the ocular surface limits the availability of iron to microorganisms and thus exerts firm control of the bacterial flora at these sites. Sequestration of iron by this protein can also inhibit the iron catalyzed production of hydroxyl radicals thereby protecting mucosal surfaces from oxydative damage. Lactoferrin has furthermore been shown to play a role in myelopoiesis, primary antibody response, lymphocyte proliferation, cytokine production, ADCC, NK cell activity, and regulation of complement activation. The observations described above indicate that lactoferrin, besides control of the bacterial flora, may regulate inflammatory reactions occurring on the ocular surface.
 ...
PMID:The role of lactoferrin in the nonspecific immune response on the ocular surface. 212 4

A simple post-embedding technique for the electron microscopical detection of lectin-binding sites using thin sections of tissues embedded in the resin LR White is described. With this technique, no prior etching of the sections is necessary. The cellular fine structure is well preserved and permits close correlation of the labelling to distinct cellular compartments. After mild aldehyde fixation (4% formaldehyde and 0.5% glutaraldehyde for 30 min), enterocyte brush border, vesicles and lysosomes as well as goblet cell Golgi apparatus and mucin are intensely stained after 30-60 min. The hydrophilia and penetrability of LR White is shown by the formation of oxidized diaminobenzidine reaction product arising from horseradish peroxidase-conjugated lectins. The precipitate not only covers the surface of the sections but is also formed within the resin, as is revealed on cross-sections through thin and semithin sections. The addition of 0.2 M solutions of the appropriate inhibitory sugars prevented staining, which indicates a specific binding. Examples are given of the binding of gold-, ferritin- and peroxidase-conjugated lectins for the purpose of detecting glycoconjugates in various intracellular compartments.
 ...
PMID:Post-embedding localization of glycoconjugates by means of lectins on thin sections of tissues embedded in LR white. 242 41

The currently accepted concept of iron absorption proposes first the entry of iron into the intestinal mucosal cell through the brush border membrane. It is a relatively slow process. In the cell, the iron may be transferred to plasma or become sequestered by ferritin. The latter becomes unavailable for transfer to plasma and is exfoliated and excreted. In iron deficiency and idiopathic hemochromatosis, the rate of iron uptake into the intestinal mucosal cell is increased and entry into ferritin is decreased, whereas the rate of transfer to plasma remains constant. The reverse occurs in case of secondary iron overload. It is currently accepted that a transferrin, whose levels increase in iron deficiency, enters the intestinal lumen from the liver via bile, where it may sequester iron and bring it into the cells by the process of endocytosis. Iron presented as inorganic ferric or ferrous salts may also be absorbed, though the more soluble ferrous salts are adsorbed much more rapidly. Heme iron is absorbed very effectively, though it is not subject to regulation by the individual's iron status to the same extent as is inorganic iron absorption. Brush border membranes apparently contain saturable iron receptors for inorganic iron, but whether or not the absorption process requires energy is an open question. Absorption of iron may also be affected by its availability; different food components affect iron absorbability to a different extent.
 ...
PMID:Biochemistry of nonheme iron in man. II. Absorption of iron. 266 38

Antibodies (AbMVM) were produced in rabbits to microvillous membranes isolated from hamster small bowel. Incubation of frozen sections of hamster small bowel with fluorescein-labeled AbMVM showed specific reaction with brush borders, but not with other intestinal cellular components. Electron microscopy with ferritin-conjugated AbMVM localized the antigens more precisely to the surface mucopolysaccharide coat of the brush borders. AbMVM also reacted with the brush border of colon and of proximal renal tubules of hamsters but not with those of hamster stomach or gall bladder. It also reacted with the brush borders of some rat and human tissues, but not with those of rabbits. In addition, fluorescent-labeled AbMVM combined specifically with cell walls of some yeasts, but not of several bacteria. AbMVM also contained a weak precipitin to a component of hamster serum, which migrated like prealbumin in immunoelectrophoresis.
 ...
PMID:Antibodies to intestinal microvillous membranes. I. Characterization and morphologic localization. 496 81

The localization of gamma-Glutamyltransferase (gamma-GT, E.C.2.3.2.2) was studied on isolated tubular fragments from rat kidney cortex immunocytochemically. Monospecific antibodies raised in the goat against rat kidney gamma-GT were used. Antigoat immunoglobulin from the rabbit conjugated with ferritin was used for visualisation of the antibody binding sites. The enzyme was found to be localized at the brush border membrane of proximal tubules, the luminal membrane of distal tubules and collecting duct segments. The enzyme could further be localized on the antiluminal or basolateral cell membranes of proximal and distal tubular fragments, whereas no such localization was verified for collecting duct segments. The role of this basolateral gamma-GT localization in context with the kidney's ability to extract over 83% of the renal arterial glutathione (GSH) input during a single passage is discussed.
 ...
PMID:Immunocytochemical localization of gamma-glutamyl-transferase on isolated renal cortical tubular fragments. 614 46


1 2 3 Next >>