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  • 1980-1984  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Effects of Monensin and Colchicine on Myelin Galactolipids (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 43 (1984), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Monensin and colchicine have been used in a variety of systems to disrupt functioning of the Golgi apparatus and transport of Golgi-derived vesicles to the plasma membrane. In this study the effects of monensin and colchicine on the synthesis of cerebroside and sulfatide and their appearance in myelin were examined to determine whether these myelin components are processed through the Golgi apparatus. Brain slices from rats 17 days old were incubated with [3H]galactose and [35S]sulfate to label cerebroside and sulfatide. Myelin was isolated on sucrose density gradients. Fractions highly enriched in cerebroside and sulfatide were prepared from homogenates and myelin fractions by lipid extraction, alkaline methanolysis, and in some cases TLC. Monensin at 0.1 μM had no significant effect on synthesis of these galactolipids as measured by incorporation of [3H]galactose into cerebroside or [35S]sulfate into sulfatide in homogenates. However, appearance of [35S]sulfatide in the myelin fraction was reduced to 49% of control, while appearance of [3H]cerebroside was not significantly reduced. Colchicine from 1 mM to 0.1 μM had effects similar to monensin, that is, appearance of [35S]sulfatide in myelin was depressed, but again [3H]cerebroside was not affected. Incorporation of [35S]sulfate into sulfatide in homogenate was 93% of control, while appearance of [35S]sulfatide in the myelin fraction was depressed to 58% of control. The inhibition of appearance of sulfatide in myelin by colchicine and monensin is consistent with the view that sulfation of cerebroside occurs in the Golgi and that sulfatide is transported via Golgi-derived vesicles to the forming myelin membrane. Further, synthesis of cerebroside and its appearance in myelin are not inhibited by colchicine or monensin, indicating that cerebroside destined for myelin is not processed through the Golgi apparatus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1984.tb06689.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Biochemical Expression of Mosaicism in Female Mice Heterozygous for the Jimpy Gene (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 42 (1984), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Expression of the jimpy gene in heterozygous females was analyzed by measuring galactolipid synthesis in brain during early myelination. Sulfatide labeling in brains of heterozygous females at 13–14 days is decreased to 40–80% that of female littermates who do not carry the jimpy gene. The activities of ceramide galactosyl transferase and cerebroside sulfotransferase and levels of myelin basic protein were similarly depressed. Since the jimpy gene was maintained with the Tabby gene in these studies, the effect of the Tabby gene on these parameters was examined and found to have no effect. These biochemical findings indicate that myelination is retarded in the brains of heterozygous jimpy females during the second week of development. However, at 18 days and thereafter, sulfatide labeling is less reduced, suggesting that the oligodendrocytes in brain attempt to compensate, in agreement with morphologic studies which show that myelin is decreased in brain during early development, but appears normal in adult animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1984.tb02704.x
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetics of Entry of P0 Protein into Peripheral Nerve Myelin (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 37 (1981), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Sciatic nerves from 9-day-old rat pups were removed, sliced into 0.4-mm sections, and incubated with [3H]fucose or [14C]glycine precursors. The nerve slice system gave nearly linear incorporation of [3H]fucose as a function of time for 3 h, after an initial lag of ˜30 min for homogenate and ˜60 min for myelin. Incorporation of [3H]fucose at constant specific radioactivity was directly proportional to exogenous fucose levels over the range 3.0 × 10−8m to 1.5 × 10−6m. Analysis of labeled proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that greater than 50% of labeled glycoprotein was P0, with no other major constituents. This system was used in fucose-chase experiments to determine that a period of ˜20 min elapses between fucosylation and assembly of P0 into myelin. Cycloheximide inhibition of protein synthesis was used to determine that a period of ˜33 min elapses between protein synthesis and appearance of P0 myelin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1981.tb05304.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of Monensin on Assembly of Po Protein into Peripheral Nerve Myelin (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 39 (1982), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The ionophore monensin has been used in a variety of systems to block secretion of glycoproteins or assembly of glycoproteins into membranes. We examined the effects of monensin on assembly of the Po glycoprotein into PNS myelin, and compared this agent with the glycosylation inhibitor tunicamycin in our system. Sciatic nerves from 9-day-old rat pups were sliced and incubated in vitro. Electron microscopy of the Schwann cells in slices incubated with monensin revealed extensive swelling of the Golgi complex. Incubation with 10−7M monensin inhibited total protein synthesis by about 20% and fucose incorporation into protein about 35%. Following isolation of myelin, proteins were separated by sodium dodecyl sulfate gel electrophoresis. Monensin inhibited the appearance of Po in myelin, while causing its accumulation in a denser membrane fraction. In addition, a slightly faster-migrating species of Po labeled with both [3H]fucose and [14C]glycine was observed in all fractions. Assembly of basic proteins into myelin was not affected. Preincubation with 10 μg/ml tunicamycin for 30 min prior to incubation with [3H]fucose and [14C]glycine for 2 h resulted in a 65% decrease in [3H]fucose incorporation into Po, and the appearance of a new [14C]glycine-labeled peak that migrated in the region of the 23K protein reported by Smith and Sternberger. [3H]Fucose incorporation was inhibited earlier, and to a greater extent, than protein synthesis. Our results show that processing of the Po glycoprotein is sensitive to both monensin and tunicamycin, and that monensin partially blocks assembly of Po into myelin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1982.tb11502.x
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Cerebroside Sulfotransferase in Golgi-Enriched Fractions from Rat Brain (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 38 (1982), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Golgi-enriched fractions were prepared from brainstems of 17-day-old rats by first floating off myelin, then fractionating the remaining pellet by a series of differential and density gradient centrifugations in sucrose. Fractions enriched in Golgi membranes were recovered at 0.46/0.76 m and 0.76/0.87 m interfaces on the final sucrose gradient as indicated by morphology and the biochemical markers thiamine pyrophosphatase and [3H]fucose-labeled glycoprotein. Morphology of the two fractions indicated very little contamination with myelin lamellae; however, the presence of significant levels of 2′, 3′-cyclic nucleotidase in the lighter fraction suggested a contribution from oligodendroglial or myelin-related membranes. Cerebroside sulfotransferase was highly enriched in the lighter Golgi-enriched fraction relative to the denser fraction, the post-34, 880 x g microsomes, and the myelin-like fraction. In contrast, ceramide galactosyl transferase was more evenly distributed among the fractions. Our results show a more highly localized distribution of sulfatide synthesis than of galactocerebroside synthesis, probably in Golgi membranes or oligodendroglia-related membranes with similar properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1982.tb10875.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of Monensin on Posttranslational Processing of Myelin Proteins (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 40 (1983), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Rat brain slices were incubated with [3H]palmitic acid and [14C]glycine to label the lipid and protein moieties, respectively, of myelin proteolipid protein (PLP). The effects of monensin on posttranslational processing of proteins were examined by measuring the appearance of [14C]glycine- and [3H]palmitate-labeled proteins in myelin and myelin-like fractions. At 0.01 and 0.10 μM, monensin did not appreciably affect total lipid or protein synthesis; higher concentrations caused increased inhibition. Monensin at 0.10 μM markedly decreased the appearance of [14C]glycine-labeled PLP in myelin, but had little effect on the 14C basic proteins or the incorporation of [3H]palmitic acid into total or myelin PLP. The same relative effect was apparent at higher monensin concentrations. In the myelin-like fraction, monensin at 0.10 μM also depressed entry of [14C]glycine into protein comigrating with PLP, and again had no effect on incorporation of [3H]palmitic acid. In addition, monensin increased the [3H]palmitate label associated with two high-molecular-weight proteins in the myelin-like fraction with no concomitant increase in [14C]glycine label.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1983.tb13575.x
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