Red cells, ferritin, and iron storage during amphibian development.

Both circulating red blood cells and the liver store iron in ferritin during larval (bullfrog) or embryonic (mouse) development. In contrast, circulating red cells in adults do not store iron and the liver is the main site of iron storage and ferritin. The structure of larval red cell and liver ferritin was compared to adult liver ferritin and the redistribution of iron was measured during amphibian metamorphosis when larval red cells are replaced by adult red cells. Liver ferritin from larvae and adults was very similar in terms of amino acid composition, subunit size, and microheterogeneity (observed by isoelectric focusing) with 80 to 90% of the ferritin composed of three subtypes with an apparent p1 of 4.8 to 5.1; the remainder of ferritin (10 to 20%) was composed of four subtypes in the pI range 5.1 to 5.5. In contrast to liver ferritin, larval red cell ferritin had a higher serine and glycine content. Moreover, the microheterogeneity of red cell ferritin was quantitatively unique with all seven subtypes (PI range 4.8 to 5.5) present in approximately equal amounts. In SgFe-labeled prometamorphic tadpoles, the specific activity (disintegrations per min per pg of iron) of red cell ferritin was 22,000, liver ferritin was 5,000, and hemoglobin was essentially unlabeled. At the end of metamorphosis the specific activity of liver ferritin was 4,000 and hemoglobin was 13,000; the liver and red cells accounted for 70% of the radioactivity, the remainder being in the carcass. Developmental changes in iron content included a slight increase in the liver, a decrease in the carcass and red cells, and a transient increase in the plasma (maximum when 50% of the red cells were replaced). No change was observed in the ferritin content of the liver or liver parenchymal cells. The data suggest that the iron in red cell ferritin was preferentially used for the hemoglobin of the first adult red