Iron and transferrin distribution in reticulocytes incubated with heme synthesis inhibitors.

A high level of non-heme iron (either labelled or unlabelled) in mitochondria, ferritin and low-molecular-weight pool of reticulocytes was induced by preincubation with isonicotinic acid hydrazide or penicillamine together with either 59Fe- of 56Fe-labelled transferrin. Addition of apotransferrin during reincubation of 59Fe-labelled reticulocytes was accompanied by the transfer of 59Fe from low-molecular-weight pool to transferrin, which was found in the reticulocyte cytosol both free and bound to a carrier. Similarly, when cells were reincubated with 125I-labelled transferrin, more 125I-labelled radioactivity was found, in both free and carrier-bound transferrin peaks, in reticulocytes with a high level of low-molecular-weight cold iron than in control ones. These results suggest that transferrin enters reticulocytes and takes up iron from low-molecular-weight pool.