Metal‐Combining Properties of Human Lactoferrin (Red Milk Protein)

Abstract

Human lactoferrin, the red iron‐binding protein from milk, was prepared by chromatography on DEAE‐cellulose of the milk proteins soluble in 2 M ammonium sulfate. Several preparations differing in iron content were obtained. Apolactoferrin was prepared by dialyzing the protein against 0.1 M citric acid. Saturation experiments with iron ascorbate indicated the iron: protein ratio at saturation to be 0.025 micromoles of metal per mg of protein. Assuming 80,000 to be the molecular weight of lactoferrin, this would correspond to a ratio of two iron atoms per molecule. With copper, a similar molar proportion at saturation was obtained. Gasometrie measurements were used to calculate the amount of carbon dioxide liberated upon dissociation of the metal‐protein complexes by acidification. One mole of CO 2 was freed per atom of iron or copper.