Transferrin binding and iron transport in iron-deficient and iron-replete rat reticulocytes

Three aspects of iron metabolism were studies in reticulocytes from iron-deficient, phlebotomized, and phenylhydrazine-treated rats: (1) the number of transferrin binding sites; (2) the uptake of 59Fe-transferrin; and (3) the ability of cytosol to mobilize 59Fe from 59Fe-labeled reticulocyte plasma membrane. The number of transferrin binding sites, assayed by measuring the binding of 125I-labeled transferrin to reticulocytes, were similar in iron-deficient and phlebotomy-induced reticulocytes, 66,000 and 75,000 binding sites/cell, respectively, but were about doubled, 120,000 binding sites/cell, in phenylhydrazine-induced reticulocytes. Uptake of 59Fe into iron-deficient reticulocytes was about one-half that for phlebotomy-induced reticulocytes and one-quarter that for phenylhydrazine-induced reticulocytes, the rates of uptake being measured as 21,540, 41,233, and 79,600 molecules of 59Fe per minute per cell, respectively. The mobilizing activity of cytosol free iron-deficient reticulocytes was also about one-half that of cytosol from phlebotomy-induced reticulocytes and about one-quarter that of cytosol from phenylhydrazine-induced reticulocytes. These results indicate that instead of a compensatory increase in these aspects of iron metabolism, the iron-deficient reticulocyte had a decreased ability to transport iron.