On the assimilation of iron by the developing red blood cell

Abstract

Reticulocytes are the last immature cell type in the erythrocyte maturation process. Unlike the mature erythrocyte they are able to take up iron from transferrin, the serum iron binding protein, and incorporate it into several macromolecules, the most important of which is hemoglobin. The transferrin and reticulocyte interaction was shown to be highly influenced by the methods used for transferrin iodination and saturation with iron as well as reticulocyte induction. Serum was also shown to affect the iron donation process. Although a great deal of work has been done on the iron assimilation process, the actual mechanisms involved remain unclear. In an effort to gain insight into the nature of the process, rabbit reticulocyte ghosts were prepared from whole cells previously incubated with ⁵⁹Fe³⁺ -transferrin-CO ²₃⁻for 45 minutes. A fraction of the ⁵⁹Fe taken up by the cells remained membrane bound. Fresh, unlabeled reticulocyte cytoplasm was incubated with these specifically labeled ⁵⁹Fe-ghosts. The ⁵⁹Fe was mobilized and incorporated into ferritin, hemoglobin, and two smaller molecular weight components. The smaller of the two was found to have a molecular weight of 6,000 and to bind non-heme ferrous ion reversibly. It was found to be protein in nature and was able to mobilize iron from the ghosts and donate it for hemoglobin and ferritin biosynthesis. The other component contained non-heme iron and had a molecular weight of near 18,000..