RESUMO
Techniques of cell separation were used to isolate murine erythroid cells at different stages of maturation. The number of transferrin receptors in these cell populations was assayed by measuring binding of 125I-labelled transferrin. Nearly 23 times as many receptors were found in the least mature cells, chiefly pronormoblasts, as in reticulocytes. Iron transport, determined by measurement of the rate of 59Fe uptake from 59Fe-labelled transferrin, was proportional to the number of receptors at all stages of differentiation. Electron microscope radioautographic studies of the interaction of 125I-labelled transferrin with erythroid precursor cells demonstrated that 15-33% of cell associated transferrin was intracellular in erythroid precursors.
