Porcine Thyrotropin

The properties of porcine thyroid‐stimulating hormone and its subunits, which had not yet been fully characterized, are presented. A new procedure is described for the isolation of the hormone using only ion‐exchange chromatography and gel filtration. The system, presented in details for porcine thyrotropin was also applied with success for the preparation of bovine and human thyrotropins. The porcine hormone prepared either by the new chromatographic procedure or by countercurrent distribution exhibited identical physicochemical and biological characteristics. The subunits α and β of porcine thyroid‐stimulating hormone were also obtained by a new procedure. In this method, the native hormone was incubated in acidic urea and the chains were than separated by ion‐exchange chromatography. The subunits were submitted to a complete characterization. The amino‐acid composition of the α subunit of porcine thyrotropin was found identical to that of α chain of porcine luteinizing hormone. Its amino‐terminal sequence was NH 2− Thr‐Met‐Glx indicating that the α‐chain of porcine thyrotropin is shorter by six amino acids than its bovine counterpart. The porcine β subunit differs markedly in its amino‐acid composition from the bovine β chain particularly with respect to lysine, histidine, tyrosine, threonine and glutamic acid. Phenylalanine is the amino‐terminal residue of the polypeptide chain. The carbohydrate compositions of the two subunits are presented. Porcine thyrotropin differs from its bovine counterpart in that it contains sialic acid, present only in the α subunit.