New Kinetic Role for Serum Ferritin in Iron Metabolism

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Abstract
Summary. The role of the iron in serum ferritin was investigated with regard to iron kinetics. Serum (or plasma) was fractionated on a sucrose gradient by ultra‐centrifugation to separate iron in ferritin from other iron‐containing components in serum. After injection of heat‐treated [59Fe]RBC in rats, detectable labelling of the serum ferritin fraction was brief, between 20 and 40 min. The labelling of other iron components in the serum was maximal between 1 and 2 hr. No labelling of the serum ferritin fraction was detected after intravenous administration of [59Fe]‐transferrin in man and in the rat, or after [59Fe]haemoglobin‐haptoglobin or oral [59Fe2+]citrate in the rat. These results indicate that iron in serum ferritin originates in part from the degradation of haemoglobin in senescent red cells and that this labelled ferritin is cleared from the serum rapidly.In normal rats, [59Fe]ferritin, purified from rat liver and injected intravenously, disappeared from the serum at an exponential rate with a half‐disappearance time (HDT) of 4 min. After 1 hr 97% of the label had accumulated in the liver. After a delay of 24 hr, increasing amounts of label appeared in the RBC to an estimated maximum of 70–80% at 5 days. Conditions which increased or decreased rates of synthesis of haemoglobin altered the percentage of [59Fe]ferritin incorporated into haemoglobin, but these conditions did not change the rate of removal of [59Fe]ferritin from the serum by the liver. These results indicate that the iron in serum ferritin is cleared from the serum much more rapidly than transferrin‐bound iron. The data are consistent with the passage through serum ferritin of a major portion of the iron that is released from the degradation of red cell haemoglobin in the RE system.

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