The location of prekallikrein in the rat pancreas [proceedings].

receptors was investigated. IgG from Graves’ sera with high thyroid-stimulating antibody activity were diluted in IgG from a pool of normal human serum (so that each sample contained the same amount of total IgG) and incubated overnight at 0°C with labelled thyrotropin and membranes solubilized with 0.5 % Triton. The mixtures were then analysed by chromatography on Sepharose or by poly(ethy1ene glycol) precipitation. The binding of labelled thyrotropin to the soluble-receptor preparations was inhibited in a dose-dependent manner by thyroid-stimulating antibodies (Fig. 2). Gel filtration of mixtures of antibodies, labelled thyrotropin and soluble thyrotropin-receptor preparations indicated that a trimolecular complex consisting of the three components was not formed. Further, analysis of mixtures of antibodies and labelled thyrotropin only by gel filtration and poly(ethy1ene glycol) precipitation showed that no direct interaction between them occurred, i.e. the antibodies did not demonstrate thyrotropin-binding activity. These data suggested that the binding of thyrotropin and thyroid-stimulating antibodies to the thyrotropin receptors was mutually exclusive, and that thyrotropin and the antibodies interacted with the same receptor molecule.