Difference in Isoelectric Point of 27S and 19S Thyroidal Iodoproteins Determined by Isoelectric Focusing

SummaryThe 19S thyroid soluble iodoprotein (thyroglobulin) differs from the 27S thyroid soluble iodoprotein, its dimer, in isoelectric point. Purified 19 and 27S obtained from extracts of human thyroids after surgery or after in vitro culture of the same material, when submitted to isoelectric focusing showed distinct bands of precipitation. These results are interpreted to mean that the total net charge available on the surface of the dimer is different from that of the monomer. The implication of this finding to the structure, iodination, and possibility of recognition by specific proteinases of the dimer is discussed.