Distribution of the Molecular Weight and Chemical Form of Intrinsic Iron Compounds in Soybeans

Abstract

The distribution of the molecular weight and chemical form of intrinsic iron in a soybean aqueous supernatant and in its in vitro peptic digest was determined. 50% of the total iron in soybean was extracted into the aqueous supernatant. All of the iron in the aqueous supernatant was bound to some ligands, and nearly all was localized in the protein fraction. More than 50% of the iron in the protein fraction was localized in the >100, 000 molecular weight fraction. The effects of SDS, 2-mercaptoethanol and/or EDTA on the binding status of the intrinsic iron were studied. Almost all the iron compounds in large molecules was converted to lower-molecular-weight (10, 000 to 20, 000) fractions after treating with SDS, with no change in the binding capacity. No change in the distribution of the molecular weight of iron in the protein fraction was observed after treating with 2-mercaptoethanol. The soy component was found to strongly bind iron. No released iron was observed by chromatography in the presence of SDS or 2-mercaptoethanol, and only about 15% of the total iron in the protein fraction was taken away by EDTA in the absence or presence of SDS or 2-mercaptoethanol. In vitro peptic digestion caused half the total iron in the >100, 000 molecular weight fraction to be moved to the fraction with a molecular weight of 10, 000 to 20, 000, the remaining half continuing to be bound to the macromolecules.