Receptor binding and internalization of immobilized transcobalamin II by mouse leukaemia cells.
Membrane transport of vitamin B12 (cyanocobalamin; Cbl) into mammalian cells is mediated by the serum protein transcobalamin II (TCII). In mouse leukaemia L1210 cells, TCII- Cbl binds to membrane receptors in a rapid, temperature-independent step and is internalized by a slow, temperature-dependent process. To delineate the location of receptors on these cells, we have constructed a visual probe by covalently coupling purified TCII- Cbl to submicrometre latex particles (minibeads). We report here that when L1210 cells are incubated with minibeads containing TCII- Cbl at 4 degrees C and examined by scanning electron microscopy (SEM), the particles are found attached predominantly to microvilli. Incubation of the cells at 37 degrees C results in the internalization of the minibeads. As visualized by transmission electron microscopy (TEM), this endocytotic process seems to occur in clathrin-coated pits and vesicles at the cell surface.[1]References
- Receptor binding and internalization of immobilized transcobalamin II by mouse leukaemia cells. Takahashi, K., Tavassoli, M., Jacobsen, D.W. Nature (1980) [Pubmed]
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