The Uptake of Ferric Iron by Rat Liver Ferritin in Vivo and in Vitro

S ummary . The incorporation of ferric iron labelled with ⁵⁹Fe into rat liver ferritin has been studied in whole animals, into liver homogenate and into purified protein. Uptake of Fe³⁺ into purified rat liver ferritin followed a pattern similar to that with horse spleen ferritin given Fe²⁺ and an oxidant. The distributions of iron incorporated as a function of molecular iron content obtained in vivo resembled the in vitro patterns for iron contents above 500 Fe atoms/molecule and times after injection of up to 12 h. At larger intervals a maximum label moved to molecules of highest iron content as the molecules accumulated more iron. The apparently reduced uptake of injected ⁵⁹Fe into molecules of low iron content might be due either to the chase of cold iron through an existing iron pool or the presence of functionally different ferritins at more than one anatomic site within the cell.