Binding of Apotransferrin to K562 Cells: Explanation of the Transferrin Cycle

The binding of apotransferrin to the transferrin receptor on the surface of human leukemic K562 cells was found to be significantly less tight than that of the holoprotein, diferric transferrin. The finding that both ligands displayed linear Scatchard plots with similar receptor number ≈ 150,000 per...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1983-04, Vol.80 (8), p.2263-2266
Main Authors: Klausner, Richard D., Ashwell, Gilbert, Van Renswoude, Jos, Harford, Joe B., Bridges, Kenneth R.
Format: Article
Language:English
Subjects:
Apoproteins
apotransferrin
Asialoglycoproteins
Cell biology
Cells, Cultured
Endocytosis
erythroleukemia
Humans
Hydrogen-Ion Concentration
Internalization
K562 cells
Kinetics
Leukemia, Erythroblastic, Acute
Ligands
man
Phthalates
Receptors
Receptors, Cell Surface - metabolism
Receptors, Transferrin
Transferrin - metabolism
Transferrins
Washing
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Summary:The binding of apotransferrin to the transferrin receptor on the surface of human leukemic K562 cells was found to be significantly less tight than that of the holoprotein, diferric transferrin. The finding that both ligands displayed linear Scatchard plots with similar receptor number ≈ 150,000 per cell) and mutually inhibit each other's binding suggested that they bind to the same receptor. Both the dissociation and association rate of apotransferrin were markedly increased (28-fold and 15-fold, respectively) at pH 7.2 compared to pH 4.8. Using the values of these binding parameters, we propose a mechanism to account for the recycling of transferrin subsequent to internalization and residence within an acidic nonlysosomal organelle where iron is removed.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.80.8.2263