TSH action on iodination in FRTL-5 cells.

This study shows that the Fisher rat thyroid cell line (FRTL-5) can iodinate thyroglobulin (Tg) in an selective way. The Tg-iodination is TSH dependent and shows a optimum at 10-100 microU TSH/ml. Intracellularly, Tg and various other non Tg-related proteins are iodinated in a TSH dependent fashion. Tg added to the medium is specifically iodinated, this occurs already in microgram amounts, in contrast to many other proteins present in the medium. Only albumin, present in mg amounts is clearly iodinated in a lower degree than Tg. Albumin iodination is not clearly dependent of TSH. Since catalase added to the medium prevents the iodination of albumin but not of newly synthesized Tg we suggest that intracellular iodination must exist.