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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Metabolic relations in the termite - protozoa symbiosis: Temperature effects (1942)
    Philadelphia : Wiley-Blackwell
    Journal of Cellular and Comparative Physiology 19 (1942), S. 211-219 
    Details
    ISSN: 0095-9898
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1030190209
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  • 3
    Electronic Resource
    Electronic Resource
    Functions of the IGFs in early mammalian development (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 35 (1993), S. 421-426 
    Details
    ISSN: 1040-452X
    Keywords: Preimplantation embryo ; Protein database ; Growth factors ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The identification of growth factors and/or receptors produced by mammalian embryos or present in the maternal reproductive tract is of basic interest, as well as having practical application. Early studies established that receptors binding insulin and the insulin-like growth factors (IGFs) are expressed by preimplantation mouse embryos. These studies have been confirmed at the molecular level using RT-PCR techniques. In addition, high resolution electron microscopy has shown that insulin is internalized by the cells of the blastocyst stage mouse embryo, and that immunologically intact insulin is detectable in the cells of the trophectoderm and inner cell mass. Similar studies with gold labelled IGF-I have shown that this ligand is also bound and internalized by mouse blastocysts. However, although all blastocysts express receptors that bind IGF-I on the basolateral cell surface of the trophectoderm, only 30% exhibit apically located receptors. In order to elucidate the functions of IGFs in early mouse development, we are in the process of constructing protein databases for embryos at the eight-cell and blastocyst stage. By the use of the database, it should prove possible to elucidate targets of growth factor action. © 1993 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080350417
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  • 4
    Electronic Resource
    Electronic Resource
    Proline oxidase in cultured mammalian cells (1977)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 91 (1977), S. 369-376 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We sought a cultured cell line with Proline Oxidase activity to study the regulation and physiologic role of the enzyme in mammalian tissues. Among the cell lines tested, only LLC-RK1 cells, derived from rabbit kidney, had significant Proline Oxidase activity; the Km for proline of the enzyme from these cells was similar to that for the liver enzyme. LLC cells, Proline Oxidase positive, were able to convert proline to CO2. In contrast, CHL cells, Proline Oxidase negative, did not have this capability. The presence of Proline Oxidase in LLC cells and the absence of the enzyme in fibroblasts suggest that Proline Oxidase may serve as a marker enzyme for distinguishing parenchymal kidney cells from fibroblasts in culture. Cells transformed by SV40 virus and cells transformed by methylcholanthrene had activities higher than the parent cell line, but this effect of transformation could not be generalized to all transformed cells. Finally, L-hydroxy proline at 100-fold greater concentration than substrate L-proline failed to decrease proline oxidation. This finding suggests distinct degradative enzymes for these two amino acids.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040910306
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  • 5
    Electronic Resource
    Electronic Resource
    Stimulation of the hexosemonophosphate-pentose pathway by pyrroline-5-carboxylate in cultured cells (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 110 (1982), S. 255-261 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Δ1-Pyrroline-5-carboxylic acid, an intermediate in the interconversions of proline, ornithine, and glutamate, is a potent stimulator of glucose oxidation through the hexosemonophosphate-pentose pathway. The effect is observed in cultured human fibroblasts, Chinese hamster ovary cells (CHO-K1), and rabbit kidney cells (LLC-RK1). In human fibroblasts, the magnitude of the stimulation of the hexosemonophosphate-pentose pathway is dependent on the concentration of added pyrroline-5-carboxylate and the effect is observed over a wide range of glucose concentrations. The mechanism of the effect is related to the generation of oxidizing potential in the form of NADP+ by pyrroline-5-carboxylate reductase concomitant with the conversion of pyrroline-5-carboxylate to proline. In LLC-RK1 cells, a cell line unique in having proline oxidase activity, proline also stimulated hexosemonophosphate-pentose pathway activity. Although pyrroline-5-carboxylate markedly stimulated the hexosemonophosphate-pentose pathway, it had no effect on glucose metabolism in the Embden-Meyerhof pathway or the tricarboxylic acid cycle. Since the hexosemonophosphate-pentose pathway is a source of ribose-5-phosphate, the precursor of phosphoribosyl pyrophosphate, the effect of pyrroline-5-carboxylate on the hexosemonophosphate-pentose pathway may link amino acid and nucleic acid metabolism.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041100306
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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    The importance of ornithine as a precursor for proline in mammalian cells (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 98 (1979), S. 475-481 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Ornithine aminotransferase catalyzes the reversible transamination of L-ornithine to δ1-pyrroline-5-carboxylate, the immediate precursor of proline. The direction and flux through this pathway in mammalian cells has not been established. Glutamate has generally been considered to be the most important precursor for proline biosynthesis, but recent studies in xiphoid cartilage indicate that a significant fraction of cellular proline is derived from ornithine. Using newly isolated mutant Chinese hamster ovary cells with defined defects in the proline biosynthetic pathways, we now have established that cells can grow at a maximal rate with ornithine as the sole source of proline. Furthermore, we have measured the rate of proline formation from ornithine (1.6 nmol/h/106 cells). Future studies with these mutant Chinese hamster ovary cells may offer insight into the regulatory mechanism which coordinates proline biosynthesis from ornithine and glutamate.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040980306
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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
    Regulation of glutamine synthetase and glutaminase activities in cultured skeletal muscle cells (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 120 (1984), S. 197-203 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Glutamine is synthesized in skeletal muscle, released to the circulation, and transported to other tissues, where it may provide important substrate for gluconeogenesis, ammoniagenesis, and energy-yielding pathways. With the ultimate goal of delineating the factors that control glutamine production and release by skeletal muscle, we have studied the regulation of two key enzymes, glutamine synthetase and glutaminase, in the L6 line of rat skeletal muscle cells grown in monolayer culture. The cultured myotubes were found to have glutamine synthetase and phosphate-dependent glutaminase activities. Glutamine synthetase activity was increased following incubation (1) in glutamine-free medium (threefold); (2) in medium containing high glutamic acid concentrations (fourfold); and (3) in medium supplemented with dexamethasone (threefold). In each case the increase in glutamine synthetase activity required several hours to reach a maximum and was prevented by cycloheximide, suggesting that the change occurred through increased enzyme biosynthesis. No substances tested were found to affect glutaminase activity. We conclude that glutamine synthetase in cultured skeletal muscle is responsive to substrate, product, and hormonal regulation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041200213
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