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

Using transmission electron microscopy, we have studied the interaction of alpha 2 macroglobulin (alpha 2 M) with the surface of cultured fibroblasts. When cells were incubated for 2 h at 4 degrees C with ferritin-conjugated alpha 2 M, approximately 90% of the alpha 2 M was diffusely distributed on the cell surface, and the other 10% was concentrated in "coated" pits. A pattern of diffuse labeling with some clustering in "coated" pits was also obtained when cells were incubated for 5 min at 4 degrees C with alpha 2 M, fixed with glutaraldehyde, and the alpha 2 M was localized with affinity-purified, peroxidase-labeled antibody to alpha 2 M. Experiments in which cells were fixed with 0.2% paraformaldehyde before incubation with alpha 2 M showed that the native distribution of alpha 2 M receptors was entirely diffuse without significant clustering in "coated" pits. This indicates that some redistribution of the alpha 2 M-receptor complexes into clusters occurred even at 4 degrees C. In experiments with concanavalin A(Con A), we found that some of the Con A clustered in coated regions of the membrane and was internalized in coated vesicles, but much of the Con A was directly internalized in uncoated vesicles or pinosomes. We conclude that unoccupied alpha 2 M receptors are diffusely distributed on the cell surface. When alpha 2 M-receptor complexes are formed, they rapidly cluster in coated regions or pits in the plasma membrane and subsequently are internalized in coated vesicles. Because insulin and epidermal growth factor are internalized in the same structures as alpha 2 M (Maxfield, F.R., J. Schlessinger, Y. Schechter, I. Pastan, and M.C. Willingham. 1978. Cell, 14: 805--810.), we suggest that all peptide hormones, as well as other proteins that enter the cell by receptor-mediated endocytosis, follow this same pathway.
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PMID:alpha 2 Macroglobulin binding to the plasma membrane of cultured fibroblasts. Diffuse binding followed by clustering in coated regions. 9 73

The method for preparing a stable, biologically active, covalently linked ferritin--insulin complex has been modified to provide a 25-fold increase in yield compared to the original procedure while reducing the molar fatio of ferritin to insulin to 1:1 from 40:1. Ultrastructural studies of isolated adipocytes revealed specific binding of ferritin--insulin to the cell surface in irregular clusters associated with the glycocalyx coating. The number of ferritin--insulin molecules observed was consistent with the number of sulin molecules observed was consistent with the number of receptors calculated from 125I-labeled insulin binding studies. The ferritin--insulin was not observed in the cytoplasm of the cell but was found on the convave side of surface connected vesicles. These surface connected vesicles were part of an alveolar-like system of plasma membrane invaginations which project in various directions in the cytoplasm and by thin sectioning can appear as pinocytotic-like microvesicles. The morphological observations on ferritin--insulin binding were supported by the finding that 125I-labeled insulin binding was almost exclusively localized to highly purified plasma membranes isolated by fractionation of adipocytes after incubation with 125I-labeled insulin. These data supported the theory that insulin did not need to enter a cell to cause biological effects and was consistent with the negative cooperativity concept of insulin binding to cell receptors.
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PMID:Ultrastructural localization of insulin receptors on adipocytes. 17 64

Binding sites for specific molecules at the cell surface can be localized with the electron microscope in thin-section, freeze-etch and shadow-casting preparations. The receptors tested were binding sites to concanavalin A (Con A) labelled with haemocyanin and binding sites to insulin labelled with ferritin. Con A-binding sites were localized in endocrine cells of the pancreas and insulin-binding sites in isolated liver plasma membranes. The relevance of the topographical distribution of the binding sites to cell membrane organization is discussed.
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PMID:Membrane topology as revealed by the binding of macromolecules. 18 Dec 24

The distribution of anionic sites on the membranes of rat pancreatic B cells and of their storage granules has been studied by the use of a visual probe of cationic ferritin. Membranes of isolated storage granules possessed a net negative charge which was apparently evenly distributed; the number of anionic sites was not markedly altered by prior incubation of the granules with neuraminidase or with 10(-5) to 2 X 10(-3) M calcium chloride. Distribution of charges along B cell plasma membranes was less uniform but was similarly unaffected by alterations of calcium concentration, or by neuraminidase treatment. However, during the fusion of plasma membrane and granule membrane which occurs in exocytosis, the emerging granule membrane was found to be devoid of anionic sites. The implications of these findings for the regulation of insulin secretion by exocytosis are discussed.
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PMID:Distribution of anionic sites on surface of B cell granule and plasma membranes: a study using cationic ferritin. 33 20

The distribution of glutathione-insulin transhydrogenase (glutathione: protein-disulphide oxidoreductase, EC 1.8.4.2) in isolated rat hepatocytes that had been first treated with rabbit antiserum against purified rat liver transhydrogenase and then with ferritin-conjugated goat anti-rabbit gamma-globulin was examined by electron microscopy. In cells with intact plasma membrane, the immunoferritin labeling of glutathione-insulin transhydrogenase was observed on a few external microvillous projections at the outside of the cell. In cells with breaks in the plasma membrane, the immunoferritin labeling appeared extensively on smooth vesicles just inside the plasma membrane and on smooth endoplasmic reticulum extending to and including the outer nuclear membrane, in addition to the external microvillous projections. There was some immunoferritin labeling on rough endoplasmic reticulum and on the inner surface of the plasma membrane. The mitochondria and the outer surface of the plasma membrane of the cell did not show the ferritin labeling. Control parallel samples in which the antiserum was substituted with normal (i.e. non-immune) serum or with neutralized antiserum (prepared by absorption with the transhydrogenase) showed little or no immunoferritin labeling. These results are consistent with the idea that gluthalione-insulin transhydrogenase probably synthesized in the endoplasmic reticulum and that the transhydrogenase accessible to cell surface (or found in the isolated plasma membrane preparations) probably represents a functional continuity between the endoplasmic reticulum and the plasma membrane.
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PMID:Insulin degradation. XXIII. Distribution of glutathione-insulin transhydrogenase in isolated rat hepatocytes as studied by immuno-ferritin and electron microscopy. 33 61

Insulin was modified with d-biotin-N-hydroxysuccinimide ester in dimethylformamide. Mono-, di-, and triacylated insulins were separated by preparative isoelectric focusing. Monoacylated derivatives (isoelectric point 5.1) were fractionated twice on DEAE-cellulose to yield pure N epsilonB29-biotinylinsulin. The structure of the product was established by amino acid analysis before and after deamination. N epsilonB29-biotinylinsulin had biological activity indistinguishable from insulin on glucose oxidation and lipid synthesis assays using isolated rat epididymal fat cells. Complexes of N epsilonB29-biotinylinsulin with avidin, having essentially all but one binding site filled with biotin, were prepared in order to obtain a 1:1 insulin:avidin ration. The elicited identical maximal biological responses, but showed a potency decreased to 5% of that of insulin. Such complexes conjugated with ferritin will provide a useful tool in the development of electron microscopic stains of insulin receptors.
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PMID:N epsilonB29-(+)-biotinylinsulin and its complexes with avidin. Synthesis and biological activity. 62 Nov 98

These studies were designed to investigate the cytologic localization and topographic distribution of insulin receptors in human placental villi. Biochemical studies showed placental villi to specifically bind 125I-insulin. Radioautographic studies showed the specific binding to be localized to the surface of the syncytial trophoblast. Topographic distribution of insulin binding was determined with ferritin-insulin. Initial studies using ferritin-insulin containing some oligomers of ferritin revealed the insulin receptors to be specifically associated with the glycocalyx region of the surface membranes of microvilli. No insulin receptors were detectable in association with the intermicrovillous plasma membrane even though its glycocalyx is in direct continuity with the glycocalyx of microvilli. Monomeric ferritin-insulin showed the same nonuniform distribution of the insulin receptor, which suggests that there is not complete freedom of lateral mobility of the insulin receptors in the surface membrane of this tissue. The insulin receptors were found to occur as singletons or in groups of two or more. Incubations with monomeric ferritin-insulin at 4 degrees or with tissue prefixed with formaldehyde showed that the groups of insulin receptors were naturally occurring, i.e., they are present prior to and independent of insulin binding and thus not secondary to ligand-induced aggregation. The physiologic meaning of the nonuniform distribution and the groups of insulin receptors is unclear at present.
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PMID:Nonuniform distribution and grouping of insulin receptors on the surface of human placental syncytial trophoblast. 64 42

Ffty asymptomatic members of a kindred with familial hemochromatosis were studied in an effort to clarify some of the physiologic abnormalities present in the pre-cirrhotic or latent stage of the disease. Using excess hepatic iron as a marker for inheritance of hemochromatosis, results of liver biopsies on 31 family members suggest an auto-somal dominant mode of inheritance with incomplete expressivity. In addition to a relationship between alcohol intake and excess liver iron, there was a strong association between the level of alcohol intake and the presence of hepatic fibrosis in those subjects with excess iron stores. Both serum iron and transferrin saturation were significantly higher in family members with iron overload than in those who were not affected. Only transferrin saturation was significantly correlated with the severity of hepatic iron deposition. Studies of glucose tolerance (OGTT, IVITT, glucose clamp studies) demonstrated a defect in carbohydrate metabolism associated with deficient insulin secretion and insulin resistance, both of which were related to the degree of hepatic iron depostion. In this kindred we have found no evidence for a contribution of inheritance to the carbohydrate intolerance of hemochromatosis. Iron overload was not related to activity of hepatic collagen proline hydroxylase or urinary excretion of peptide-bound hydroxyproline. Serum ferritin, previously thought to be a reliable marker of reticuloendothelial iron stores, was normal in 19 of 20 family members with iron overload.
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PMID:Familial hemochromatosis: characteristics of the precirrhotic stage in a large kindred. 87 Jul 91

CIA, ferritin, ACTH, cortisol, TTH, T3, T4, insulin, CT and PTH levels were assayed radioimmunologically in the blood serum of 227 patients with lung cancer, stages I-IV, 134 cases of chronic nonspecific diseases of the lung, 28 patients with benign tumors of the lung and 30 healthy subjects. Adrenaline tests were carried out in 160 of them. Similar shifts were observed in hormone profile in both cancer and non-cancer patients. The predictive value of the hormone tests for stage I-II cancer appeared higher than in those for CIA and ferritin. However, the diagnostic value of a single test of marker proved insufficient for its practical use. Adrenaline tests identify fine disturbances in endocrine regulation and considerably raise the predictive value of such indicators as ACTH, insulin, TTH, T3, T4 and calcitonin. To assure high effectiveness of the use of basic radioimmunological data, a combination of indexes should be prepared for each case, and it should include, apart from basic levels of markers, their post-test values and indexes of reactivity.
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PMID:[The dynamics of the hormonal and tumor marker levels in response to adrenaline administration in lung cancer patients]. 134 47

Endocrine abnormalities in patients with chronic renal failure are well documented. The present study aimed to assess the influence of long-term erythropoietin (EPO) therapy on endocrine abnormalities in haemodialyzed patients. Two groups of haemodialyzed patients, each of which comprised 17 subjects, were examined. The first one treated by EPO (EPO group) while the second one did not receive this hormone (NO-EPO group). A complete biochemical and hormonal check-up was performed before and at the 3, 6, 9 and 12 months of the study period. Normal values for the estimated parameters were obtained in appropriately selected sex and age-matched healthy subjects. After EPO therapy an increase of the haematocrit value from 21.8 +/- 0.9% to 32.6 +/- 0.9% was observed which was accompanied by a significant decline of plasma ferritin and saturation of transferrin. In patients of the NO-EPO group a significant although less marked rise of the haematocrit value (21.4 +/- 0.4% to 24.2 +/- 0.6%) was also noticed. EPO therapy did not change electrolytes (Na, K, Ca, inorganic phosphate), osteocalcin, creatinine, glucose and alkaline phosphatase plasma levels as well as plasma concentrations of calcium related hormones (PTH, calcitonin, 1.25(OH)2D3) and vasopressin (AVP). EPO treatment induced a significant decline of somatotropin (HGH), prolactin (PRO), follitropin (FSH), lutropin (LH), ACTH, cortisol, plasma renin activity, aldosterone, insulin (IRI), glucagon (IR-G), pancreatic polypeptide (PP) and gastrin plasma levels and an increase of plasma estradiol, testosterone and atrial natriuretic peptide (ANP). These EPO induced endocrine alterations were restricted mostly to the first 6 months of EPO administration.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Influence of long-term erythropoietin therapy on endocrine abnormalities in haemodialyzed patients. 145 6


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