[Rapid analysis of transferrin-iron complexes by isoelectric focusing and radioactive densitometry on gel]

The analysis of the molecular forms of transferrin-iron complexes with 59Fe, was carried out using an isoelectric focusing method on commercially available polyacrylamide plates (PAG plates pH = 4-6,5, LKB). Depending upon the saturation degree of proteins with iron, apotransferrin (pI = 6,1), transferrin-Fe3+ (pI = 5,8), transferrin-2 Fe3+ (a) (pI = 5,5) and transferrin-2 Fe3+ (b) (pI = 5,3) were put forward. When the protein was saturated with iron, a double band was observed which was assigned to the microheterogeneity of the protein and depends upon the sialic content. The quantitative analysis was carried out by studying 59Fe radioactivity distribution directly on the plate. As a control, a specific staining of proteins was achieved. The interpretation of the results is difficult if such a method is used, as some bands are not attributed. Through an unspecific staining, the UV-visible densitometry is not satisfactory enough. The proposed method allows a fast analysis of transferrin-metal complexes labeled with radioactive metals. Such a method would be adaptable to the study of other complexes as transferrin-67Ga, transferrin 111In in order to determine the binding site of metal on the protein and its metal content.