Iron transport intermediates in human reticulocytes and the membrane binding site of iron-transferrin

1. 1. The iron-bearing components obtained by chromatographic fractionation of human reticulocytes have been further studied in relation to their role in intracellular iron transport. 2. 2. In timed and chaser experiments membrane component A, like haemoglobin, behaved as an end product, while membrane component B1 and cytosol component C behaved as intermediates. 3. 3. We confirm that component B2, molecular weight 230 000, behaves as a complex of iron-transferrin and its membrane binding site. 4. 4. Sulphydryl inhibition with p- hydroxymercuribenzoate does not affect iron-transferring binding, but blocks the pathway between components B2 and B1 leading to an accumulation of the iron-transferrin-receptor complex. 5. 5. The results suggest that initially iron moves from the iron-transferrin-receptor complex (B2) to membrane component B1 from which it may diverge into membrane component A or follow the main pathway through cytosol component C to haemoglobin.