Bovine Thyrotropin

Abstract A contercurrent distribution system has been devised for bovine thyrotropin which permits easy removal of several impurities, including one of the peptide chains of luteinizing hormone. The remaining chain of luteinizing hormone, which has a number of properties similar to those of thyrotropin, can then be removed by gel filtration. The thyrotropin is biologically active after the countercurrent distribution and no evidence has been found for the separation of subunits as occurs with luteinizing hormone. The active thyrotropin contains more methionine, tyrosine, and lysine than previously reported. Electrophoresis of the reduced and S-carboxamidomethylated derivatives of thyrotropin and luteinizing hormone in urea-containing gels reveals polymorphism beyond that exhibited by the native hormones. In the case of thyrotropin, the added polymorphism does not seem to represent dissociation into subunits. Polymorphism of native luteinizing hormone obtained as a by-product of the preparation of thyrotropin has also been found. Because the luteinizing hormone which is most difficult to separate from thyrotropin by chromatography cannot be distinguished from thyrotropin by conventional gel electrophoresis, new electrophoretic criteria have been developed to establish when thyrotropin preparations are free of luteinizing hormone or either of its peptide chains. Immunochemical studies show that an antiserum directed against one of the chains of luteinizing hormone crossreacts with both thyrotropin and luteinizing hormone, although, under the same conditions, each of the two hormones does not significantly cross-react with antisera prepared against the native form of the other. Data on the composition of the two chains of luteinizing hormone are given which confirm earlier observations of others that thyrotropin and one of the chains of luteinizing hormone have similar molar ratios of amino acids.