The nuclear associated endoplasmic reticulum and membrane biogenesis in MPC-11 cells.
The incorporation of 3H-glucosamine, 3H-choline and 14C-fucose into subcellular fractions of MPC-11 cells was studied. After a 20 min period of labelling with both 3H-glucosamine and 3H-choline, greatest incorporation was observed in nuclear-associated endoplasmic reticulum (NER). 14C-fucose, however, was incorporated to a greater extent in endoplasmic reticulum (ER) membranes. Pulse-chase experiments with 3H-glucosamine showed a loss of radioactivity from NER and a simultaneous increase in the ER fraction. In comparison to NER, ER membranes were poorly labeled with 3H-glucosamine after a 20 min pulse. Following a 2 h incubation there was a 12 fold increase in radioactivity in ER membranes in comparison to a 1.2 fold increase in NER. There were no individual differences between subfractions of ER membranes with respect to 3H-glucosamine content after the pulse, or following the 2 h incubation. The results indicate that the NER is a major, early site of the synthesis of 3H-glucosamine labeled membrane glycoproteins, and that these proteins migrate into other ER membranes early after their synthesis.
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Department of Biochemistry, University of Bergen, Norway.
D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002794:Choline / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005643:Fucose / Q000378:metabolism*; D005944:Glucosamine / Q000378:metabolism*; D006023:Glycoproteins / Q000096:biosynthesis; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000096:biosynthesis
D006023:Glycoproteins; D008565:Membrane Proteins; D005643:Fucose; D005944:Glucosamine; D002794:Choline