Iron uptake and ferritin synthesis in human erythroblasts

The erythroblasts from four normal bone marrows were enriched by using an anti-myeloid monoclonal antibody (TG-1), and a polyclonal antibody against mononuclear cells to effect complement mediated lysis of unwanted cells. The erythroblasts were cultured for 2 h in medium containing [59Fe]transferrin and [3H]-leucine, then fractionated on Percoll gradients according to their density. Whole cell iron uptake by early erythroblasts was greater than in the dense late erythroblasts. In all marrows, iron uptake into ferritin was highest in fractions containing the earliest erythroblasts and decreased with increasing erythroblast maturity. In three of the four marrows this paralleled the pattern of ferritin synthesis. It seems likely that apoferritin is synthesized in response to the amount of iron taken into the cell and this iron is incorporated within the protein shell to form ferritin.