Binding added iron to various milk proteins.

Binding of an added radionuclide to milk protein and casein components of cow's milk fractionated by the combination of Sephadex G-150 gel filtration and diethylaminoethyl-cellulose chromatography was determined. Iron-59 labeled ferric chloride was added directly to raw whole milk at a concentration of .02 and 10 ppm isotope and carrier, respectively, and held overnight at 4 C. Five milliliters of the skin milk were chromatographed on a Sephadex G-150 column and fractionated into casein, whey protein, and nonprotein materials. The casein fraction was chromatographed on a diethylaminoethyl-cellulose column and separated into its components, alphas-, beta-, and kappa-caseins. Casein bound about 85% of the added iron in skim milk; of this amount, 72, 21, and 4% were associated with the alphas-, beta, and kappa-caseins.