A Chinese hamster ovary cell mutant defective in the receptor-mediated endocytosis of several unrelated ligands (Robbins, A. R., S. S. Peng, and J. L. Marshall, 1983, J. Cell Biol., 96:1064-1071) failed to accumulate iron provided in the form of diferric transferrin. Analysis of the steps of the transferrin cycle indicated that binding and internalization of transferrin proceeded normally in mutant cells. However, the mutant appeared unable to dissociate iron from transferrin, as evidenced by release of diferric transferrin from the mutant versus apotransferrin from the parent. Uptake of ferric ions from the growth medium was enhanced in the mutant.

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