Isolation of five active thyrotropin components from human pituitary gland

A procedure is described for the isolation of human pituitary thyroid-stimulating hormone (thyrotropin). The starting material was a side-fraction provided by the earlier developed process for the purification of growth hormone from whole frozen pituitaries. This fraction was further purified by successive chromatography on Bio-Gel P-150, Bio-Gel HT hydroxyapatite, and SP-Sephadex C-50. The resulting preparation was obtained in yields of 10 mg/kg of pituitary tissue and had a thyrotropin potency of 11 units human Research Standard A/mg as measured by a specific radioimmunoassay. Contamination by other pituitary hormone activities was low. In the ultracentrifuge a single sedimenting boundary was registered with an s20,w value of 2.7 S. The molecular weight as determined by sedimentation-equilibrium experiments was 34 000 in phosphate buffer, pH 7.0, and 17 700 in 1 M propionic acid. This thyrotropin preparation was, however, electrophoretically heterogenous. Following preparative polyacrylamide gel electrophoresis five different components associated with thyrotropin activity were isolated. Isolation on a preparative scale of electrophoretically homogeneous human thyrotropin has not earlier been reported. One of the thyrotropin components was characterized with respect to molecular weight and amino acid composition. The data were consistent with a molecular weight of 33 000 from sedimentation-equilibrium analysis at pH 7 and with 268 amino acid residues per molecule.