Non-Hematin Iron in Erythrocytes

Abstract

The structure of ferritin, a crystalline iron-protein compound containing 23% iron, has been discussed in previous papers. 1 , 2 , 3 The iron appears to be present in the form of micelles of colloidal iron hydroxide characterized by Fe atoms containing 3 unpaired electrons, and markedly different from various synthetic colloidal iron hydroxides. Crystals containing this iron have been isolated in relatively high yield from spleen, liver and red bone marrow of various species 4 strongly suggesting that this iron arises from hemoglobin decomposition. Since the amount of non-hematin iron in horse spleen is so great (1.8 to 2.0% Fe in dry weight of spleen), it appeared that a histological study of this tissue might reveal the distribution and perhaps the origin of the iron.

A very sensitive test for inorganic iron including the colloidal ferric hydroxide of ferritin is the production of a black insoluble iron sulfide with H₂S. When a piece of horse spleen was teased out into a drop of 1% saline, most of the red blood cells appeared crenated. Cells occasionally appeared which were swollen, had a smooth outline and contained hemoglobin. On the addition of a drop of 1% saline containing H₂S to the tissue, some of the hemosiderin granules became black immediately (3, Fig. 1), thus indicating the presence of iron in them. Other hemosiderin granules remained yellow, indicating that they lacked the non-hematin iron. Some macrophages could be seen to contain large hemosiderin granules which turned black (4, Fig. 1). A number of the crenated erythrocytes developed several very tiny black spots scattered on their membranes (1, Fig. 1). In the presence of H₂S the swollen erythrocytes took on a smooth grey appearance which within a minute became finely granular and darker grey.