Carrier mediated iron transport through erythroid cell membrane.

The transport of iron through erythroid cell membrane was studied in a model system, measuring ferrous iron uptake by reticulocytes. It was found that these cells were able to take up ferrous iron and to incorporate it into haem at a rate similar to that observed when diferric transferrin was the iron donor. No comparable iron uptake could be measured when the metal was provided as Fe3+-citrate or when reticulocytes were replaced by mature erythrocytes. The involvement of endogenous transferrin in the Fe2+ uptake by reticulocytes could be excluded, since proteolytic treatment of the cells had no significant effect on the process. Fe2+ uptake by reticulocytes followed saturation kinetics, characteristic to carrier mediated transport processes. Kinetic analysis of the data revealed the following apparent transport parameters: Km = 8.8 +/- 3.8 microM; Vmax = 1.1 +/- 0.2 ng/10(8) reticulocytes/min. These results indicate that a high affinity, carrier mediated iron transport system is present in the reticulocyte membrane, ensuring the efficient translocation of the metal through the membrane barrier between the site of its release from transferrin and the site of its utilization.