Preferential Synthesis of Thyroxine from Early Iodinated Tyrosyl Residues in Thyroglobulin

摘要: Abstract A double labeling procedure was employed to determine whether the tyrosine residues in thyroglobulin that are iodinated first also those most readily converted thyroxine. Goiter containing less than 1 atom of iodine per molecule with 131I at relatively low levels iodination (5 20 atoms molecule) and afterward 125I higher (20 60 molecule). Iodinations were carried out either chemically I3-, or enzymatically thyroid peroxidase. Three different sets conditions for labeling: (a) second iodinations both performed I3-; (b) chemically, enzymatically; (c) enzymatically. The enzymatic used experiments. An index "preferential synthesis" defined assessing there preferential use labeled [131I]tyrosyl thyroxine synthesis. Evidence synthesis obtained all above procedures, but convincingly when When applied casein fibrinogen, two proteins previously shown form upon peroxidase, no evidence obtained. Similarly, disruption native structure by exposure 5 m guanidine resulted failure observe Preferential synthesis, therefore, is not a general characteristic capable forming on Results present investigation support view plays an important role facilitating formation. It appears contains tyrosyl whose function hormone iodination.