Antimicrobial Properties of Iron-Binding Proteins

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Abstract
Iron-binding proteins of the transferrin type occur widely in various biological fluids. Serum transferrins (serotransferrins) are necessary to transport iron into the immature red cells of the bone marrow for hemoglobin synthesis, and to accept iron from the reticuloendothelial system as the latter destroys senescent or damaged red cells and releases iron from hemoglobin. The discovery of the transferrins is, however, closely related to another property thereof, i.e., the inhibition of bacterial growth. Thus, in 1944, Schade and Caroline discovered that raw egg-white was bacteriostatic and that this activity could be abolished by the addition of iron to the egg-white (Schade and Caroline, 1944). Two years later it was shown that the antimicrobial substance present in the egg-whites was a transferrin-type protein called conalbumin (Alderton et al., 1946), which had been discovered half-a-century earlier by Osborne and Campbell (1900), who were totally unaware of either the antimicrobial or the iron-binding properties of the protein. Schade and Caroline (1946) also described the antimicrobial properties of serotransferrin, which could also be abolished by the addition of iron. It is today recognized that serotransferrin has a function in host-defense mechanisms in addition to its function as a mediator of iron-cell interactions.