THE ALTERNATE IRON TRANSPORT PATHWAY - MOBILFERRIN AND INTEGRIN IN RETICULOCYTES

Iron transport in reticulocytes is known to occur via the well-describ ed transferrin-receptor-endosome pathway An alternative pathway for ir on transport independent of transferrin has been postulated in reticul ocytes and other cells. Transport of iron into reticulocytes from ferr ic citrate solutions was Shown to be saturable and independent of tran sferrin. During transport of iron from ferric citrate, both cell surfa ce integrins, and a soluble protein, mobilferrin, were labelled. This demonstrated that the reticulocyte transferrin independent pathway for iron transport involved integrins and mobilferrin similar to intestin al absorptive cells. This pathway would be expected to transport iron into cells under conditions of iron overload and was capable of provid ing iron for haemoglobin synthesis. Mobilferrin was also radiolabelled when radioiron labelled transferrin was incubated with reticulocytes and this occurred with a different time course than was observed follo wing reticulocyte exposure to radiolabelled ferric citrate. This sugge sted that mobilferrin may serve as an intermediary in both pathways.