Binding of THS by normal and TSI-containing globulins.

: 125I-TSH was found to be specifically, bound to globulins from healthy persons and from patients with Graves' disease (GSI negative). Bmax 1.2 pmol mg-1, Kd 1.2 mga pmol-1 was found for TSI negative globulins from normal sera and Bmax 32 pmol mg-1, and Kd 53 pmol-1 mg for TSI positive ones. Maximum binding appeared within a 1 incubation period and was little dependent on temperature. The pH optimum for the binding was found between 7--8. There was a linear correlation between the protein content and the specific binding of the globulin preparations. LH, FSH, ACTH, prolactin and insulin competed with TSH for the binding sites only in relatively very high concentrations. The binding sites appear to be macromolecules, since they were eluted from Sephadex G-200 at the void volume.