Observations on Fe⁵⁹ Labeled Bone Marrow Ferritin

Qualitative studies were carried out to determine the nature of the nonhemoglobin protein or proteins of human bone marrow which incorporate radioiron during in vitro incubations of this tissue. The labeled fraction was studied chiefly by following the behavior of the radioactive iron and comparing it with ferritin isolated from human spleen. Two types of labeled ferritin were identified in the nonhemoglobin fraction. One, a "fast" ferritin, was of greater electrophoretic mobility than spleen ferritin in starch granules and appeared possibly to be the chief incorporator of transferrin-bound iron. The second, or "slow" ferritin, was identical in electrophoretic mobility with spleen ferritin and contained only a tiny percentage of the radioiron incorporated into "fast" ferritin. No other iron-labeled nonhemoglobin components were observed, although their possible presence cannot be discounted.