Abstract
I131-TSH was made by the reaction of elemental iodine (I2127) and TSH preparation (Pretiron) containing 5.15% tyrosine, using radioiodine I131 as a tracer. In 1 JS of TSH preparation the amount of tyrosine was 1.83γ and 1 JS of TSH was saturated with about 2.5γ of iodine and then its activity was lost completely with iodination, but it was possible to made variously active TSH by various iodination. Tyrosine residue was changed to DIT and/or MIT in the case of iodination of TSH. Therefore, it was ascertained that tyrosine residue mainly participated in this iodination and absolutely necessary residue for the activity of TSH was tyrosine. So we can calculate the amounts of the iodine bound. TSH. If the molecular weight of TSH is 25, 000 as reported by Bates and Condriffe (1960), 1 JS of TSH would be saturated and inactivated with 0.2γ of iodine.
It is pressumed that the action of Lugol's solution in Grave's disease is the inactivation of TSH by the formation of iodinated TSH in the thyroid gland before the appearance of TSH effect. The addition of Mercazole mainly inhibits the iodination of TSH by the reduction of elemental iodine, and free I131 is not removed from I131-TSH by the treatment with Mercazole.
