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

We studied the binding and biological activities of gold-insulin complexes to develop a complex with properties identical to native insulin. Stabilizing amounts of insulin absorbed to 5-, 10-, or 15-nm gold particles resulted in complexes with 40-327 insulin molecules per gold particle and 4-111 times the biological activity of unlabeled insulin, based on the molar concentration of gold complex. These data suggested that these complexes behaved as multivalent ligands. Gold-insulin complexes were prepared with 5% of the stabilizing insulin concentration and were stabilized with bovine serum albumin. This resulted in a complex with 5-7 insulin molecules per 10-nm gold particle, which stimulated glucose oxidation in rat adipocytes and competed with [125I]-insulin for binding to the insulin receptor identically to unlabeled insulin on an equimolar basis. The organization and distribution of insulin receptors occupied by this monovalent-behaving gold-insulin complex were virtually identical to previous observations using monomeric ferritin-insulin. Since multivalent ligands may affect receptor binding, re-distribution, and intracellular processing, the use of electron-dense probes that resemble the unlabeled ligand in biological and binding properties is appropriate when studying receptor dynamics of in vivo or in vitro biological systems. The gold-insulin complex developed in this study should serve this function.
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PMID:Preparation and characterization of a colloidal gold-insulin complex with binding and biological activities identical to native insulin. 327 10

Diabetes mellitus was observed in 29 of 448 patients with thalassaemia major attending seven Italian centres. Twelve patients, at onset of clinical diabetes, presented with an asymptomatic glycosuria, 13 with ketosis, and four with ketoacidosis. All were diagnosed after 1979, at a mean age of 17 years. Mean age at diagnosis of diabetes was lower in patients born in the last two decades. In these patients transfusions were started at a younger age and pre-transfusion haemoglobin concentration, serum ferritin concentration, incidence of liver disease, and the presence of a family history of diabetes were higher than in patients born previously. Although 27 (93%) cases had iron chelating treatment the mean serum ferritin concentration was 5600 micrograms/l; 25 (92%) of these patients had signs of liver impairment. The determination of C peptide in 10 patients showed a wide variation in pancreatic beta cell function, and insulin requirements ranged between 0.15 and 1.72 U/kg body weight. Metabolic control was generally poor. The onset of diabetes mellitus was followed in most patients by the appearance of other endocrine or cardiac complications, or both. Fourteen patients died within three years of presenting with overt diabetes. Haemosiderosis, liver infections, and genetic factors seemed to be crucial in diabetes development. Thalassaemic patients developing clinical diabetes mellitus are at high risk for other complications and should be strictly monitored, especially for thyroid impairment.
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PMID:Insulin dependent diabetes in thalassaemia. 334 50

Monomeric ferritin-labeled insulin (Fm-Ins), a biologically active, electron-dense marker of occupied insulin receptors, was used to characterize the internalization of insulin in 3T3-L1 adipocytes. Fm-Ins bound specifically to insulin receptors and was internalized in a time- and temperature-dependent manner. Fm-Ins was found in cytoplasmic vesicles within 5-10 min at 37 degrees C and subsequently was observed in multivesicular bodies and lysosomes. In addition, small amounts of Fm-Ins were associated with nuclei after 30 min. The number of Fm-Ins particles observed in nuclei continued to increase in a time-dependent manner until at least 90 min. In the nucleus, several Fm-Ins particles usually were found in the same general location--near nuclear pores, associated with the periphery of the condensed chromatin. Addition of a 250-fold excess of unlabeled insulin or incubation at 15 degrees C reduced the number of Fm-Ins particles found in nuclei after 90 min by 99% or 92%, respectively. Nuclear accumulation of unlabeled ferritin was only 2% of that found with Fm-Ins after 90 min at 37 degrees C. Biochemical experiments utilizing 125I-labeled insulin and subcellular fractionation indicated that intact 3T3-L1 adipocytes internalized insulin rapidly and that approximately equal to 3% of the internalized ligand accumulated in nuclei after 1 hr. These data provide biochemical and high-resolution ultrastructural evidence that 3T3-L1 adipocytes accumulate potentially significant amounts of insulin in nuclei by an insulin receptor-mediated process. The transport of insulin or the insulin-receptor complex to nuclei in this cell or in others may be directly involved in the long-term biological effects of insulin--in particular, in the control of DNA and RNA synthesis.
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PMID:Ultrastructural evidence for the accumulation of insulin in nuclei of intact 3T3-L1 adipocytes by an insulin-receptor mediated process. 354 Sep 67

In order to assess the possible effects of insulin on serum concentrations of trace metals (iron, copper, zinc) and trace metal binding proteins (ferritin, transferrin, coeruloplasmin), five normal females were studied with the hyperinsulinaemic-euglycaemic clamp technique. A 0.1 U/kg insulin bolus was administered, followed by an insulin infusion at a rate of 10 mU/kg/min for 12-16 h. Insulin levels of 1500-2000 microU/ml (9.21-12.28 nmol/l) were attained. When iron levels in serum were assayed colorimetrically, there appeared to be a progressive rise in the mean concentration during the course of the insulin infusion. Direct analysis of serum samples by atomic absorption spectrophotometry also showed that the level of non-haeme iron increased 3-fold in the serum of the subject with the lowest concentration of this metal at the start of the study. In contrast with the results for serum iron, the levels of ferritin, total iron binding capacity (transferrin), zinc, copper and coeruloplasmin were not altered in any subject during the insulin infusion or at 24 h following discontinuation of the infusion. Within 4 h of institution of the hyperinsulinaemic clamp significant reductions in serum levels of potassium, phosphorus, cholesterol, total protein and albumin were noted. As the insulin infusion progressed, the urea nitrogen, uric acid and bicarbonate levels fell as well. These observations suggest that supraphysiologic hyperinsulinaemia of 12-16 h duration may alter serum levels of iron, but not serum levels of zinc, copper or trace metal binding proteins in some individuals.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of extreme hyperinsulinaemia on serum levels of trace metals, trace metal binding proteins, and electrolytes in normal females. 354 94

Biochemical and ultrastructural studies of insulin binding and cellular processing by cultured H4IIEC3 hepatoma cells were performed. Insulin binding and intracellular accumulation were rapid and after 30 min at 37 degrees C, 65% of the total cell-associated 125I-insulin was in an acid-stable compartment. Chloroquine had no significant effect on the amount of total cell-associated insulin or the percentage of insulin in the acid-stable compartment or cell-associated insulin degradation under those conditions, but after 60-min incubations, it slightly decreased the rate of dissociation of internalized hormone. Ultrastructural analysis revealed that monomeric ferritin-insulin (Fm-I) initially bound to single or paired receptors on microvilli. Within 5 min occupied insulin receptors microaggregated and migrated to the intervillous cell surface. During the next 5-10 min occupied receptors aggregated into large clusters on the plasma membrane. Large amounts of insulin were internalized by macropinocytosis and the majority of internalized Fm-I was found in phagosomes. Less than 10% of the membrane-bound insulin was associated with pinocytotic invaginations or coated pits and less than 5% of the total cell-associated insulin was found in lysosomes. Chloroquine had no detectable effect on the amount of Fm-I or its distribution among the intracellular organelles. These studies demonstrated that, compared to previous studies with rat adipocytes or 3T3-L1 adipocytes, insulin interalization and intracellular processing in this hepatoma cell were unique. These differences provide further evidence that insulin binding and processing may be controlled by cell-specific mechanisms and that substantial heterogeneity exists in pathways previously presumed to be similar for all cell types.
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PMID:Insulin binding and processing by H4IIEC3 hepatoma cells: ultrastructural and biochemical evidence for a unique route of internalization and processing. 354 44

We prepared homogeneous populations of colloidal gold particles of various sizes. These were analyzed for size distribution and number of particles per unit volume. On exposure to increasing concentrations of insulin, myoglobin, protein A, peroxidase, serum albumin, galactosylated serum albumin, lactoferrin, transferrin, catalase, low-density lipoprotein, ferritin, and polymeric IgA, protein binding was a saturable process. Using serum albumin, we verified that a reversible equilibrium was reached within 15 minutes. Scatchard analysis of the interactions between all of these proteins and the gold particles resulted in a single component, linear relation. For a given particle size, the number of binding sites for various proteins was inversely proportional to their molecular weight. Conversely, when the size of particles was varied, the number of binding sites was directly proportional to the average area of each gold particle. All results are compatible with a monomolecular shell of protein surrounding the particle at saturation, the binding capacity being inversely proportional to the projection area of the protein. We present direct morphological evidence for this model. The affinity of the various proteins for the colloid also increased with molecular weight, and was not related to the protein isoelectric point. For globular proteins, the monomolecular shell model makes possible prediction of the number of molecules that will saturate a gold particle, if the average diameter of the gold particles and the molecular weight of the protein are known.
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PMID:A model of protein-colloidal gold interactions. 365 23

We have examined the effect of the trophic protein, nerve growth factor (NGF), on organotypic cultures of fetal rat striatum. Treatment of cultures with NGF for 10-11 days resulted in a 5- to 12-fold increase in the specific activity of the cholinergic enzyme choline acetyltransferase (CAT; EC 2.3.1.6). in a dose-dependent fashion. This effect was not elicited by insulin, ferritin, or cytochrome c, proteins similar in structure or physicochemical properties to NGF. The effect of NGF on CAT activity was specifically blocked by anti-NGF antiserum, whereas treatment with the antiserum alone did not have a significant effect on the enzyme. Immunocytochemical studies of the treated cultures, using a monoclonal antibody directed against CAT, revealed positively stained neurons exhibiting dendritic and axonal processes. NGF did not have an effect on total protein content of the striatal cultures, suggesting a highly specific effect. Moreover, levels of substance P, a peptide localized to other, noncholinergic neurons, were not altered by NGF. Substance P remained unchanged after treatment with NGF for 12 days, whereas CAT activity increased 12-fold in sister cultures. Although the mechanisms of action of NGF on striatal cholinergic interneurons remain to be determined, the marked, specific response of CAT suggests that this well-defined trophic protein may play a critical role in normal brain development.
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PMID:Nerve growth factor promotes cholinergic development in brain striatal cultures. 386 96

Six anti-DNA hybridoma autoantibodies were prepared by fusing spleen cells from unimmunized MRL/MpJ/lpr/lpr female mice with BALB/c myeloma cells. The monoclonal antibodies were analyzed by solid-phase ELISA for antigen-binding specificities. Three antibodies (62A2, 85A5, and 43B2) bound ssDNA, TNP-KLH, and recognized an epitope(s) present on insolubilized proteins such as BSA, KLH, ferritin, and insulin. The antibodies bound, with a marked preference, TNP-KLH, either soluble or insoluble. The other three antibodies (35A1, 32C5, and 39D2) bound only ssDNA. However, this binding was inhibited by free flavinic acid. None of the six antibodies bound either cardiolipin or proteoglycans, indicating that they do not recognize the repeating negatively charge units common to cardiolipin, proteoglycans, and DNA. All six monoclonal antibodies were purified by affinity chromatography with TNP-Sepharose. Moreover, both anti-DNA and anti-TNP antibodies from sera of nonautoimmune and autoimmune mice were purified easily on TNP-Sepharose.
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PMID:Murine polyspecific antibodies. I. Monoclonal and serum anti-DNA antibodies cross-reactive with 2,4,6-trinitrophenyl derivatives. 387 76

Capillary endothelium can actively regulate vascular permeability of various serum proteins. Hormones such as insulin must interact with this capillary barrier in order to reach their respective target tissues. We have studied the binding and subsequent internalization of 125I-insulin in both native (freshly isolated) and primary cultured capillary endothelium derived from rat epididymal fat pads. Insulin association with the endothelium, internalization and degradation differed between freshly isolated and primary cultured capillaries. Specific binding in freshly isolated and cultured capillaries was temperature dependent, and was competitively inhibited in the presence of unlabelled insulin. Primary cultures of capillaries grown to confluence did not exhibit specific binding of insulin. Despite the lack of specific receptors for insulin, cultured cells vesicularly internalized insulin. Greater than 50% of the total associated insulin was not degraded by cultured endothelium. Morphological examinations using ferritin labelled insulin localized insulin associated to the capillary endothelial cell membrane and sequestered within pinocytotic vesicles. Incubation of freshly isolated capillaries with insulin stimulated the fluid phase endocytosis of 14C-sucrose; however, insulin had no effect on fluid phase endocytosis in cultured capillaries. These results indicate that capillary endothelium, isolated from rat epididymal fat, exhibit specific receptors for insulin. Binding of insulin to the capillary membrane is followed by internalization into cytoplasmic vesicles and partial degradation.
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PMID:Insulin binding and vesicular ingestion in capillary endothelium. 390 93

Monomeric ferritin-insulin and high-resolution electron microscopic analysis were used to study the organization, distribution, and movement of insulin receptors on differentiated 3T3-L1 adipocytes. Analysis of the binding to prefixed cells showed that insulin initially occupied single and paired receptors preferentially located on microvilli. The majority of receptors (60%) were found as single molecules and 30% were pairs. In 1 min at 37% C, 50% of the receptors on nonfixed cells were found on the intervillous plasma membrane and more than 70% of the total receptors had microaggregated. By 30 min only 7% of the receptors were single or paired molecules on microvilli. The majority were on the intervillous membrane, with 95% of those receptors in groups. The receptor groups on the intervillous plasma membrane could be found in both noncoated invaginations and coated pits. The concentration of occupied receptors in the noncoated invaginations and the coated pits was similar; however, ten times more noncoated invaginations than coated pits contained occupied insulin receptors. The observations in this study contrast with those reported on rat adipocytes using identical techniques (Jarett and Smith, 1977). Insulin receptors on adipocytes were initially grouped and randomly distributed over the entire cell surface and did not microaggregate into larger groups. Insulin receptors on rat adipocytes were found in noncoated invaginations but were excluded from the coated pits. The differences in the organization and behavior of the insulin receptor between rat and 3T3-L1 adipocytes suggest that the mechanisms regulating the initial organization of insulin receptors and the aggregation of occupied receptors may be controlled by tissue-specific processes. Since both of these cell types are equally insulin sensitive, the differences in the initial organization and distribution of the insulin receptors on the cell surface may not be related to the sensitivity or biological responsiveness of these cells to insulin but may affect other processes such as receptor regulation and internalization. On the other hand, the microaggregates of occupied receptors on both cell types may relate to biological responsiveness.
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PMID:Ultrastructural analysis of the organization and distribution of insulin receptors on the surface of 3T3-L1 adipocytes: rapid microaggregation and migration of occupied receptors. 392 Feb 28


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