PHYTATE MINERAL PROTEIN-COMPOSITION OF SOYBEANS - GEL-FILTRATION STUDIES OF SOYBEAN-MEAL EXTRACTS

Defatted soybean flakes were extracted, dialyzed, and chromatographed with Tris-HCl buffer (pH 8, 0.03 M) on Sepharose 6B to investigate associations of essential minerals with specific proteins or phytic acid. Eight fractions (I-VIII) were analyzed for protein and phosphorus compositions, phytic acid, Ca, Mg, K, Na, Fe, Mn, Cu, and Zn. Protein composition was also characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ultracentrifugation. Elution of agglutinin was affected by interaction with other extract components and Sepharose. Concentrations of Fe and Ca were highest in fraction IV, which was richest in glycinin and beta-conglycinin. The content of Mn and agglutinin in the dialyzed, gel-filtered extract was in a molar ratio of 1.2, close to that reported in isolated soybean agglutinin. However, 25% of the Mn and 49% of the phytic acid were in fraction VII, where the molar ratio of Mn to agglutinin was 6. Fraction VII also had the highest levels of Mg, P, and Cu per milliliter of eluent. Fraction VIII corresponded to agglutinin. Phytic acid was apparently involved in some protein-mineral associations but not in others.