Intracellular catabolism of hemoglobin and iron dextran by the rat liver

Hemoglobin injected intravenously into rats is removed primarily by the liver, and subsequently it is digested. In order to determine the intracellular site of this digestion, hemoglobin, labeled with ⁵⁹Fe in the heme moiety and ⁷⁵-Se-selenomethionine in the globin moiety, was injected intravenously into rats that were then killed at timed intervals. The livers were fractionated by differential centrifugation into nuclear, mitochondrial, lysosomal, microsomal, and supernatant fractions. At 10 minutes, both labels appeared primarily in the microsomal and lysosomal fractions; at 40 minutes, more radioactivity was found in the lysosomal fraction than in the microsomal fraction. After 3 hours, the majority of the label was in the supernatant fraction, with the ⁵⁹Fe being in ferritin. Isolated lysosomal particles, but not microsomal particles, were capable of degrading hemoglobin to small peptides. Studies of the lysosomal particles by sucrose gradient centrifugation demonstrated that the labeled particles were heterogeneous. These data are interpreted as showing that hemoglobin taken up by liver cells first appears in small endocytic vacuoles that are deficient in enzymes capable of degrading hemoglobin. These vacuoles then become more dense and at least a portion of them merge with lysosomes to form phagolysosomes which have the enzymatic capacity to digest hemoglobin. The degradation products are then released into the cell cytoplasm (supernatant fraction). Inflammation, produced in rats by sterile turpentine abscesses, blocks reutilization of iron from hemoglobin. The catabolism of hemoglobin by rats with sterile abscesses was the same as in normal rats except for progressive accumulation of nonheme iron in ferritin of the supernatant fraction. ⁵⁹Fe-Imferon, injected intravenously into rats, first appeared primarily in the supernatant fraction of the liver cells and subsequently moved to the particulate fractions. Sucrose gradient studies showed that the Imferon entered the lysosomes of the particle fraction within 4 hours after injection.