Synthesis of rat muscle ferritins and function in iron metabolism of heart and diaphragm.

Two major species of ferritin are found in heart and other muscles of the rat, which may be separated in polyacrylamide gel electrophoresis after preliminary purification. We have examined the time-course of incorporation of [3H]leucine and 59Fe into these slow- and fast-migrating ferritins in heart and diaphragm, in vivo, following intraperitoneal or intravenous injection. The results show: 1. Both species of ferritin are synthesized from amino acids in parallel with total tissue protein and receive iron in concert; consequently, there is no structural precursor/product or iron-donor/receiver relationship between them. 2. Under iron stimulation, both ferritins are synthesized at different rates within the same tissue and between tissues, and there is a correlation between tissue concentration and its rate of synthesis. In the diaphragm, the concentration and rate of synthesis of the slow-migrating species predominate, and in the heart the opposite pertains. 3. In both tissues iron is preferentially absorbed by the first species upon entry into the tissue, and this is independent of the relative concentration of the two ferritins or their iron saturation. 4. From the data on 59Fe uptake it appears that myoglobin synthesis and metabolism are considerably more active in the heart than in the diaphragm. However, neither ferritin species is a direct iron donor for myoglobin synthesis. Instead, the ferritins and myoglobin all draw their iron from a common pool, which may be of the small molecular weight type reported for intestinal epithelium and some other cells.