The Effect of Transferrin-free Serum on the Utilization of Iron by Rabbit Reticulocytes

A transferrin-free serum, produced by removing the siderophilin with a specific antitransferrin antibody, was incapable of stimulating the entry of iron into reticulocytes, unless it was reconstituted with pure transferrin-iron complex. These observations militate against the existence of serum factor(s), other than transferrin, capable of stimulating the incorporation of iron into reticulocytes. Comparing the effects of whole serum, pure transferrin, transferrin-free serum, and the latter reconstituted with pure transferrin, it was found that normal, pooled human serum augmented the utilization of intracellular iron for heme production, which transferrin alone did not achieve.