Transferrin-bipyridine iron transfer mediated by haemoproteins

Rabbit reticulocyte cytosol was able to mediate transferrin-bipyridine iron transfer in the presence of ATP. The cytoplasmic factor responsible for the mediation of iron transfer was identified as haemoglobin. Other cytoplasmic proteins and the membrane fraction were ineffective. Human alpha and beta subunits and human myoglobin were over three times more effective than human haemoglobin A. Carbon monoxide strongly inhibited the mediation of iron transfer. Oxidation of haemoglobin abolished it but methaemoglobin could be reactivated with NADH, even when azide was bound to the haem iron. Neither globin nor haem alone were able to mediate iron transfer, even when NADH was present. Together, the reconstituted methaemoglobin A could be reactivated wtih NADH. Although the physiological significance of this pehnomenon is not clear, the involvement of haemoproteins in intracellular iron metabolism seems likely.