Transferrin mediated uptake of iron is the physiological and most efficient way for introduction
of iron into vertebrate cells. Though not accepted by all investigators, receptor-mediated
endocytosis of ferric-transferrin is thought to be the normal mechanism of iron uptake.
However, the concept of this pathway does not answer many elementary questions about
the internalization of iron, its release from transferrin, its transfer to the cytosol, and the possible
existence of a transport intermediate. To contribute to the knowledge of intracellular
iron metabolism we aimed to obtain answers to the following questions: What is the nature
of the low molecular weight iron binding fraction found in reticulocytes? At what point in
the transferrin cell cycle does iron leave the endosome; and what are the conditions necessary for endosomal iron release? In chapter 3 the composition of the low molecular weight
iron binding fraction is analyzed to determine the existence of physiologically important low
molecular weight iron transporting species in the cytosol. Chapter 4 discusses in the phase
of the transferrin cycle at which iron is removed from endosomes. In chapter 5 the experimental
work is described which explores the presence of endogenous acceptor molecules
for iron released from isolated endosome
