Effect of Iron Saturation on Transferrin Uptake by Reticulocytes

Abstract

The presence of iron on the transferrin molecule increases its affinity for and sojourn time on the reticulocyte. This could be due to selective internalization of iron-containing transferrin molecules. This possibility was investigated by electron microscopic autoradiography. Rabbit reticulocytes were incubated with rabbit transferrin at 6, 33, and 72% iron saturations, and the distribution of transferrin molecules at membrane and intra-cellular locations was assessed by grain counting. The results showed that (1) both apo-transferrin and iron transferrin enter the cell interior and (2) the amount of intracellular transferrin was primarily controlled by the concentration of membrane-bound transferrin and not by its iron saturation.

Apotransferrin is internalized and distributed in the same way as holotransferrin in K562 cells

“…In trophoblast cells that are isolated from term human placenta, both apo‐Tf & Fe 2 ‐Tf ( 125 I‐labelled and 59 Fe‐labelled Tfs) were internalized by receptor‐mediated endocytosis at similar rates (Douglas and King, 1990). The results of electron microscopic autoradiography in rabbit reticulocyte showed that both apo‐Tf or Fe 2 ‐Tf (at 6, 33, and 72% iron saturation) enter the cell and the amount of intracellular Tf is primarily controlled by the concentration of membrane‐bound Tf and not by its iron saturation (Baker et al, 1982). A similar finding, that the Tf was internalized by the reticulocytes regardless of the iron content of the protein, was reported by Young et al (1984).…”