A study of the polymorphism of bovine thyrotropin preparations by immunochemistry and peptide mapping

Abstract

Immunoelectrophoresis of highly purified bovine thyroid-stimulating hormone (TSH) preparations revealed two related antigenic components. One is inactive TSH, which also can be formed from active hormone by heat denaturation. The other and major component is the hormone. This conclusion is based on experiments in which antisera previously absorbed with inactivated TSH still neutralized the hormonal activity and on the finding that the ratio of antiserum to TSH which led to precipitation of approximately one-half the antigen also led to partial neutralization in hormone assays. Furthermore the active components observed in starch-gel electrophoresis gave identical precipitin reactions with antisera to TSH preparations which consisted either of several or one of the active components. The antibovine TSH antiserum did not show significant cross reaction with other bovine pituitary glycoproteins but did cross react with ovine and porcine TSH preparations. As previously shown by others, the bovine antibody neutralized human TSH preparations; in the present study a precipitin reaction, not identical to that obtained with ovine and bovine TSH, was also demonstrated. Immunoelectrophoresis in starch gels showed the polymorphic character of TSH even when obtained from a single anterior lobe with a minimum of manipulative procedures. Peptide maps of radioiodinated partial hydrolyzates of several of the individual active components also showed them to be essentially identical. This mapping procedure, which requires only micrograms of protein, clearly distinguished the TSH from other pituitary glycoproteins with closely related properties.