Identification of transferrin receptors in reticulocytes

Experiments were performed to obtain definitive evidence for the presence of membrane receptors for transferrin on reticulocytes. Rabbit reticulocytes were incubated with 125I-labelled rabbit transferrin. The transferrin taken up by the cells was solubilized using the non-ionic detergent, Teric 12A9 (polyoxyethylene (n=9) dodecyl alcohol). The soluble extracts of the cells were examined by gel filtration and a transferrin-binding moiety of approximate molecular weight 275 000 was identified. This binding moiety was found only in reticulocytes, not in mature erythrocytes. The membrane component could bind only transferrin and not the other plasma proteins studied. Only transferrin could displace bound transferrin from the complex. Rabbit transferrin was bound more strongly than human transferrin. The binding of transferrin to the component was shown to be reversible and saturable. It is concluded from these studies that the transferrin binding component identified in the reticulocyte stroma is a true physiological receptor for transferrin.