Binding of transferrin and uptake of iron by K-562 cells

Transferrin-mediated uptake of iron has been studied in K-562 human erythroleukaemia cells. K-562 cells accumulate iron from transferrin by a temperature-dependent mechanism linearly with time for at least 150 min. At 37 degrees C the uptake reaches a saturation level of approximately 25 pmol iron/10(6) cells/h at a concentration of iron (as iron-transferrin) of 5 mumol/l. The binding of transferrin reveals saturation kinetics, at 0.2 mumol/l of transferrin specific binding amounts to 1.8 pmol/10(6) cells. Relative to the binding of transferrin the uptake of iron increases with time. The ability of K-562 cells to accumulate iron declines with days in culture by approximately 50% from day 1 to day 5. The results are compatible with iron uptake by receptor-mediated endocytosis of transferrin, dissociation of iron within the cell and exocytosis of apotransferrin.