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  • 1
    Electronic Resource
    Electronic Resource
    2,4-Dinitrophenol and Azide as Inhibitors of Protein and Ribonucleic Acid Synthesis in Anaerobic Yeast* (1967)
    s.l. : American Chemical Society
    Biochemistry 6 (1967), S. 1693-1703 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00858a018
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  • 2
    Electronic Resource
    Electronic Resource
    Computer assisted analysis of ferritin-insulin receptor sites on adipocytes and the effects of cytochalasin B on groups of insulin receptor sites (1981)
    Springer
    The journal of membrane biology 58 (1981), S. 155-160 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A computerized quantitative technique was used to analyze the distribution of ferritininsulin receptor sites on rat adipocytes and the effects of cytochalasin B on groups of receptor sites. Computer analysis of separation distances between receptor sites established that insulin receptor sites on adipocytes did not have a random distribution but have a distinct tendency to exist in groups with a maximum separation distance between particles of 400 Å. A peak in the distribution of separation distances occurred at 100–200 Å. Cytochalasin B, but not cytochalasin D, treatment of adipocytes resulted in a decrease in the number of large groups of receptor sites and a corresponding increase in single and paired receptor sites without affecting the separation distance between the remaining grouped receptors. This suggested that when cytochalasin B disrupted the bond holding receptor sites together, it caused complete disruption. These observations provided additional information on the ultrastructural characteristics of the insulin receptor. Further application of these techniques to the analysis of insulin receptors may provide the necessary structural correlates to the biochemically observed differences in insulin action in other tissues and diseased states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870977
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  • 3
    Electronic Resource
    Electronic Resource
    Differential Response of Protein Synthesis in Ehrlich Ascites Tumour Cells and Normal Thymocytes to 2,4-Dinitrophenol and Oligomycin (1967)
    [s.l.] : Nature Publishing Group
    Nature 216 (1967), S. 714-715 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The rationale for the experimental approach used in this study is the same as that described for yeast cells1. This can be summarized as follows: if uncouplers (2,4-dinitrophenol) or blockers (oligomycin) of oxidative phosphorylation inhibit protein synthesis without affecting the intracellular ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/216714a0
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  • 4
    Electronic Resource
    Electronic Resource
    Phospholipids and the regulation of pyruvate dehydrogenase from rat adipocyte mitochondria (1983)
    Springer
    Molecular and cellular biochemistry 56 (1983), S. 99-105 
    Details
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Aqueous dispersions of 4 out of 9 phospholipids added individually to the mitochondrial fraction from rat adipocytes altered the activity of pyruvate dehydrogenase in a dose-dependent manner from 1 to 300 µM. Phosphatidylserine increased and phosphatidylcholine, phosphatidylinositol and phosphatidylinositol-4-phosphate decreased enzyme activity. The stimulation of pyruvate dehydrogenase induced by phosphatidylserine may be reversed to below basal activity by phosphatidylinositol-4-phosphate and to basal activity by NaF, a pyruvate dehydrogenase phosphatase inhibitor. The inhibition of pyruvate dehydrogenase induced by phosphatidylinositol-4-phosphate may be restored to basal levels by the addition of calcium. These results suggest that phosphatidylserine activates pyruvate dehydrogenase activity through activation of the phosphatase, perhaps forming a phosphatidylserine-calcium complex. The inhibition by phosphatidylinositol-4-phosphate may be mediated by disruption of the enzyme complex. The phospholipids may play a physiological role in the regulation of pyruvate dehydrogenase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227209
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  • 5
    Electronic Resource
    Electronic Resource
    Nonreceptor mediated nuclear accumulation of insulin in H35 rat hepatoma cells (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 153 (1992), S. 607-613 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We previously demonstrated that insulin accumulated in the nucleus in several cell types and partially characterized the uptake mechanisms and pathways in H35 rat hepatoma cells. Nuclear accumulation of insulin was energy independent, time, temperature, and insulin concentration dependent, but apparently nonsaturable. This study investigated further the initial endocytotic pathways that contribute to the nuclear accumulation of insulin using trypsin treatment of the cells to prevent insulin binding to its plasma membrane receptor. Total cell-associated, intracellular, and nuclear insulin were compared in control and trypsin-treated H35 hepatoma cells. Trypsin treatment markedly decreased total cell-associated and intracellular insulin as well as the nuclear accumulation of insulin when cells were incubated with 2.8 ng/ml insulin. When the cells were incubated with 100 ng/ml insulin, trypsin treatment totally inhibited insulin binding to the plasma membrane for at least 90 min. However, intracellular accumulation of insulin was reduced by only 50% at 60 min, and trypsin treatment failed to inhibit the nuclear accumulation of insulin. Chemical extraction and Sephadex G-50 chromatography revealed nuclear associated insulin in trypsin-treated cells was identical to that in control cells incubated with either 2.8 or 100 ng/ml insulin. These results suggest that a nonreceptor mediated uptake pathway, i.e., fluid-phase endocytosis, contributed significantly to the nuclear accumulation of insulin at high insulin concentrations, but at lower insulin concentrations the receptor-mediated pathway predominated. No matter which initial endocytotic route was used to internalize insulin, the insulin apparently associated with the same nuclear matrix proteins. This association of insulin with the nuclear matrix may be involved in regulation of nuclear events such as cell growth and differentiation or gene transcription. © 1992 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041530323
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  • 6
    Electronic Resource
    Electronic Resource
    The natural occurrence of insulin receptors in groups on adipocyte plasma membranes as demonstrated with monomeric ferritin-insulinPresented in part at the 36th Annual Meeting of the American Diabetes Association, San Francisco, California. June, 1976 and at the American Society for Clinical Investigation, Washington, D.C., May, 1977. (1977)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 6 (1977), S. 45-59 
    Details
    ISSN: 0091-7419
    Keywords: adipocyte ; insulin receptor ; ferritin-insulin ; ferritin-con A ; plasma membrane ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: This study was designed to document whether the reported distribution of insulin receptors in small groups of receptor sites randomly distributed in the glycocalyx of adipocytes and isolated adipocyte plasma membranes was a naturally occurring phenomena or due to artifacts. Possible artifacts include: (1) oligomeric forms of ferritin in the ferritin-insulin preparation, (2) an uneven distribution of the glycocalyx on the plasma membrane, or (3) ligand-induced aggregation of occupied receptor complexes. Biogel A 1.5m chromatography of the ferritin-insulin conjugate revealed the ferritin in the ferritin-insulin complex to consist of 55% monomers, 15% dimers, and 30% oligomers. The monomer peak was purified (〉 95%) for use in these studies. Cationic ferritin, a glycocalyx marker, when incubated with paraformaldehyde-fixed plasma membranes, was found to be uniformly distributed on the surface of the plasma membrane indicative of uniformly distributed glycocalyx. The ability to demonstrate and inhibit ligand-induced aggregation on the isolated plasma membrane was established with a multivalent ligand, ferritin-concanavalin A. More than 66% of the ferritin-concanavalin A receptors were found in large clusters of 5 or more and 34% as singletons or clusters of up to 4 when incubated at 24°C with fresh membranes. Only 38% of the ferritin-concanavalin A receptors were in large clusters; 62% were singletons or clusters up to 4 on membranes prefixed with paraformaldehyde before incubation. The distribution of the monomeric ferritin-insulin was similar on both adipocytes and purified adipocyte plasma membranes and was consistent with earlier reports with ferritin-insulin. The quantitative distribution of the monomeric ferritin-insulin as singletons or in groups of 2-6 was comparable between the intact cells and isolated membranes incubated at 24°C. The binding of 500 μUnits monomeric ferritin-insulin per ml to the isolated plasma membranes was studied under incubation conditions similar to those used with ferritin-concanavalin A. Under all three conditions, fresh membranes at 24°C and 0-4°C and prefixed membranes at 24°C, the pattern of distribution of the monomeric ferritin-insulin as singletons or groups of 2-6 was identical, indicating that the ligand was not causing aggregation into clusters as did the concanavalin A. Thus, the occurrence of insulin receptors in small groups appears to be a natural phenomenon in the plasma membrane structure of adipocytes.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400060104
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  • 7
    Electronic Resource
    Electronic Resource
    Insulin and α2-macroglobulin-methylamine undergo endocytosis by different mechanisms in rat adipocytes: I. Comparison of cell surface events (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 133 (1987), S. 203-212 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: This ultrastructural study compared the endocytosis of a peptide hormone, ferritin-labeled insulin (Fm-I) or gold-labeled insulin (Au-I), and a non-hormonal ligand, gold-labeled alpha-2-macroglobulin-methylamine (Au-α2MGMA), by rat adipocytes. Quantitative analysis of the cell surface showed that coated pits occupied 0.4% of the adipocyte surface. This was one fifth to one tenth of that which has been reported on fibroblasts and hepatocytes, cell types in which receptor-mediated endocytosis has been extensively studied. In contrast, uncoated micropinocytotic invaginations were quite numerous and occupied 13.1% of the adipocyte cell surface. The frequency of microphinocytotic invaginations, 13.8 per μm2 of plasma membrane, was 7-12 times greater than has been reported on fibroblasts. Therefore, the ultrastructure of the endocytic apparatus on rat adipocytes was different from more commonly studied cell types. At 4°C, Au-α2MGMA concentrated within coated pits to a density that was 52 times greater than that on the uncoated plasma membrane. Au-α2MGMA was excluded from micropinocytotic invaginations by more than 93%; this exclusion was unrelated to the size of the Au-α2MGMA particle. In contrast, at 4°C, Fm-I did not concentrate within coated pits and occupied micropinocytotic invaginations in a random manner. At 37°C, coated pits accounted for all of the endocytosis of Au-α2MGMA, proving that these structures were functional despite their atypically low density. In contrast, greater than 99% of the endocytosis of Fm-I or Au-I occurred through micropinocytotic invaginations. These results demonstrated for the first time by a comparative, quantitative, ultrastructural method that insulin and Au-α2MGMA undergo endocytosis by dissimilar mechanisms on rat adipocytes. Dissimilarities in the endocytosis of insulin and Au-α2MGMA may be related to the different biological roles of these two molecules.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041330202
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  • 8
    Electronic Resource
    Electronic Resource
    Insulin and α2-macroglobulin-methylamine undergo endocytosis by different mechanisms in rat adipocytes: II. Comparison of intracellular events (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 133 (1987), S. 213-218 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A previous ultrastructural study showed that gold-labeled insulin (Au-I) and the non-hormonal ligand gold-labeled alpha-2-macroglobulin-methylamine (Au-α2MGMA) underwent endocytosis by dissimilar cell surface structures on rat adipocytes. The present ultrastructural study compared the intracellular routes taken by these two ligands in adipocytes. Intracellular Au-α2MGMA was initially found within apparent coated vesicles but Au-I was not, consistent with the previous demonstration that Au-α2MGMA underwent endocytosis by coated pits whereas Au-I was internalized by uncoated micropinocytotic invaginations. Early in the endocytic pathway, the two ligands were segregated within separate small vesicles and tubulovesicles. Au-α2MGMA was concentrated in a small number of these structures whereas Au-I was sparsely distributed among a relatively large number. Subsequently, the two endocytic pathways converged as the ligands intermingled within pale multivesicular bodies and lysosome-like structures. Au-I was less efficiently transferred to lysosomes than Au-α2MGMA since a greater proportion of intracellular Au-I remained associated with small vesicles and tubulovesicles. This study indicates that early intracellular events in the endocytic pathways of insulin and α2MGMA are distinct. These findings are discussed in light of the fundamentally dissimilar biological roles of these two molecules and the possible involvement of the endocytic pathway in the insulin signaling mechanism.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041330203
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  • 9
    Electronic Resource
    Electronic Resource
    Quantitative ultrastructural analysis of receptor-mediated insulin uptake into adipocytes (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 115 (1983), S. 199-207 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Monomeric ferritin-insulin was used as an ultrastructural marker to determine by quantitative electron microscopy the time course and route of insulin uptake in rat adipocytes. To approximate steady state membrane binding conditions prior to any internalization, adipocytes were prefixed with glutaraldehyde and incubated for 30 min with 70 nM monomeric ferritin-insulin. Electron micrographs of these cells showed that the ferritin-insulin particles were predominantly in small groups of receptor sites on the plasma membrane and in pinocytotic-like invaginations of the plasma membrane. Significant amounts of ferritin-insulin were observed in cytoplasmic vesicles of unfixed cells as early as 2 min and in multivesicular bodies and lysosome-like structures within 5 to 10 min after the addition of the ligand. Ferritin-insulin accumulation reached steady state levels in the cytoplasmic vesicles in 5 to 10 min and in the lysosome-like structures in 15 min. Little ferritin-insulin was bound to coated pits, and the relative paucity of coated pits found in adipocytes suggested that these specialized endocytotic structures have a relatively insignificant role in insulin uptake in fat cells. Quantitative analysis of the uptake process suggested that a proportion of the insulin internalized by the cell may not be transported to lysosomes, but may be recycled along with the insulin receptor to the plasma membrane.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041150215
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrastructural analysis of the organization and distribution of insulin receptors on the surface of 3T3-L1 adipocytes: Rapid microaggregation and migration of occupied receptors (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 123 (1985), S. 167-179 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: 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 non-coated 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.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041230204
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