Iron uptake from rat plasma transferrin by rat reticulocytes.

Fast and slow rat transferrins were isolated by isoelectric focusing and prepared in their di- and monoferric forms. A comparison of the rates of iron release between fast and slow monoferric transferrins when incubated with reticulocytes or injected in vivo showed no significant difference in the behavior of the two isotransferrin species. Reticulocyte uptake of diferric transferrin resulted in the removal of both iron atoms from the transferrin molecule. A twofold greater iron uptake was observed from diferric as compared with monoferric iron, provided reticulocyte receptors were saturated. It is concluded that the two species of transferrin and their individual sites function similarly in their release of iron to tissue receptors.