Immunochemical Identification of Thyroglobulin Fragments Synthesized<i>in Vitro</i>by Bovine Thyroid Polyribosomes

Abstract

14C-labeled proteins synthesized in vitro by bovine thyroid polyribosomes were studied by immunochemical methods with rabbit antithyroglobulin antiserum. Soluble proteins produced during incubation were partially precipitated by excess antithyroblobulin antibody plus anti-rabbit γ-globulin serum. The reaction could be partially blocked by altered thyroglobulin [sodium dodecyl sulfate-treated, trypsintreated or reduced and carboxymethylated (RCM)] and to a lesser extent by native thyroglobulin (TG). [14C]proteins solubilized from polyribosomes with 0.25% SDS were also partially precipitated by anti-TG serum, and precipitation was blocked only by altered TG, but the results were inconclusive due to extensive nonspecific coprecipitation. The anti-TG serum was found to contain at least 2 types of antibodies, one reacting with native TG and RCMTG and the other only with RCM-TG. These antibodies, isolated by adsorption with the appropriate antigen, were both capable of reacting with the newly synthesized [14C] proteins. The evidence indicates that reacting antigenic groups on some of the newly synthesized proteins are the same as those on altered forms of thyroglobulin but different than those which react in the native molecule. (Endocrinology85: 752, 1969)