| Abstract: | The interaction of two main protein fractions of rapeseed —the 12 S globulin and the low-molecular albumin fraction —with two phosphate-containing polyanions —phytic acid and octametaphosphate (OMP) —has been studied using turbidimetric titration and chemical analysis after precipitation. Both proteins form insoluble complexes with the polyanions below the isoelectric point. The globulin is precipitated quantitatively by both polyanions at pH 3.0. A precipitation of more than 90% of the albumin occurs by OMP, while phytic acid precipitates only 80% of this protein at pH 3.0. Increasing amounts of polyanions over the precipitation points result in a partial solubilization of albumin-polyanion complexes. The amount of polyanions bound to the proteins increases with decreasing pH. A (1:1)-stoichiometry of phytic acid binding on the globulin has been found at pH 3.0, while the ratio of phosphate groups of OMP to basic groups of globulin is only 8.0. The maximum binding of both anions at the precipitation point amounts to 0.8 mol phosphate per mol basic groups of albumin with both polyanions at pH 3.0 using turbidimetry. An excess binding of polyanions to the globulin has been found with phytic acid at pH < 3.0 and with OMP at pH 3.0 after increasing the amount of OMP over the precipitation point. |
