Gel isoelectric focusing of human-serum transferrin

Analysis of human serum transferrin on gel isoelectric focusing resolved this iron-transport protein into two iron-containing components which were identified by the use of radioactively labelled iron and iron-specific stain. These two components were found to be monoferric transferrin (Fe-transferrin) and diferric transferrin (Fe2-transferrin) with isoelectric points of 5.6 and 5.2 respectively. The estimation of the relative proportions of these two components in serum did not correspond to the calculated theoretical ratio based on random binding of iron to the two binding sites of transferrin. However, the analysis of partially resatured apotransferrin gave a ratio corresponding to a random distribution of iron. The significance of these results is discussed.