Immunoradiometric assays using antibodies to spleen and heart ferritin were combined with Mössbauer studies on normal and pathological erythrocytes. All erythrocytes examined were found to contain greater amounts of heart type than spleen type ferritin. The ferritin concentration in erythrocytes from patients with beta thalassaemia, sickle cell disease and sideroblastic anaemia is much higher than in normal cells. When the concentration of ferritin-like iron in the pathological erythrocytes measured by Mössbauer spectroscopy is compared to the total amount of ferritin assayed by the two antibodies in the same haemolysates the iron/protein ratio ranges between 0.3 and 3.4. The iron/protein ratio in iron-filled ferritin molecules is about 0.56 and values in excess of this suggest that the iron detected in these cells is a mixture of ferritin molecules, partly denatured ferritin polymers and 'haemosiderin'. There is a possibility that erythrocytes contain an immunologically distinct type of ferritin that is not detected by existing assays, but we have no direct evidence for this.
Hemoglobin and ferritin iron content have been followed during differentiation in tissue cultures of murine erythroleukemia cells (MELC) using the techniques of Mossbauer spectroscopy and electron microscopy. In undifferentiated cells grown without DMSO, only iron stored in ferritin was detected. The amount of iron in a cell grown in the presence of iron citrate is approximately 1.2 X 10(-14) g, whereas in a cell grown in the presence of transferrin the amount is approximately 0.28 X 10(-14) g. These quantities do not depend on the iron concentration in the nutrition medium in a range from 0.3 to 2.0 microgram Fe/ml and are the same for growth times between 8 hr and 7 days. Cells grown with DMSO contain, in addition to ferritin, increasing concentrations of hemoglobin. Chase experiments prove that ferritin iron participates in hemoglobin synthesis. The amount of ferritin iron reaches saturation within less than 8 hr in MELC grown with or without DMSO. In differentiating cells grown with iron citrate there is a decrease with time in ferritin iron content concomitant with the increase in hemoglobin. Cells grown with transferrin incorporate additional amounts of iron, which are approximately equal to the amounts used for hemoglobin synthesis maintaining a constant ferritin iron level. In the electron microscope, iron is seen only as ferritin within lysosomes. The density of the ferritin in lysosomes correlates with the ferritin iron concentrations determined by Mossbauer spectroscopy.
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