title: The effect of tunicamycin on the glycosylation of lactating-rabbit mammary glycoproteins.
abstract: 1. Tunicamycin inhibited the incorporation of d-[2-(3)H]mannose into dolichol-linked oligosaccharide and glycoprotein of lactating-rabbit mammary explants by approximately the same extent (approx. 30% of control value), suggesting that lipid-linked intermediates are involved in the mannosylation of mammary glycoproteins. 2. The incorporation of radioactivity from N-acetyl-d-[1-(14)C]glucosamine into dolichol-linked oligosaccharide was inhibited by tunicamycin to 32% of the control value, whereas the incorporation of the radiolabel into glycoprotein was only inhibited to 72% of the control value. 3. Considerable redistribution of label from N-acetylglucosamine to N-acetylgalactosamine was found to occur in the explants. In the presence of tunicamycin approx. 76% of the radioactivity incorporated into glycoprotein from N-acetyl-d-[1-(14)C]glucosamine was present as N-acetylgalactosamine, compared with approx. 61% in the absence of the inhibitor. Thus tunicamycin selectively inhibits the incorporation of N-acetylglucosamine into glycoprotein. 4. Radioactivity from N-acetyl-d-[1-(14)C]glucosamine was incorporated into a glycoprotein that was identified as casein by the use of a casein-specific antiserum, and also into a group of glycopolypeptides with apparent mol.wts. ranging between 40000 and 80000. N-Acetylgalactosamine was the only radioactive sugar released on strong-acid hydrolysis of the immunoprecipitated casein, whereas N-acetylglucosamine was the major radioactive residue present in the non-casein glycoproteins. Glucosamine and galactosamine were the only radiolabelled sugars detected by paper chromatography of the strong-acid hydrolysate of the protein fraction. 5. Tunicamycin inhibited the incorporation of radioactivity from N-acetyl-d-[1-(14)C]glucosamine into the glycopolypeptides with mol.wts. between 40000 and 80000 as described by polyacrylamide-gel electrophoresis, but did not affect the incorporation of label into casein. It appears that tunicamycin inhibits the incorporation of mannose and N-acetylglucosamine into a number of mammary glycoproteins by inhibiting the formation of lipid-linked intermediates, but does not inhibit the incorporation of N-acetylgalactosamine into casein.
mesh_terms: D000116:Acetylgalactosamine / Q000378:metabolism; D000117:Acetylglucosamine / Q000378:metabolism; D000818:Animals; D002364:Caseins / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005944:Glucosamine / Q000031:analogs & derivatives*; D006023:Glycoproteins / Q000378:metabolism*; D007774:Lactation; D007930:Leucine / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism; D011247:Pregnancy; D011817:Rabbits; D014415:Tunicamycin / Q000494:pharmacology*
chemical_list: D002364:Caseins; D006023:Glycoproteins; D009844:Oligosaccharides; D014415:Tunicamycin; D007930:Leucine; D000116:Acetylgalactosamine; D005944:Glucosamine; D008358:Mannose; D000117:Acetylglucosamine