Bovine, human and porcine thyrotropins: Molecular weights, amino- and carboxyl-terminal studies

Abstract

The molecular weights and end-group analyses of bovine, human, and porcine thyrotropins (TSH) are reported. Both the hormones and their S-carboxymethyl derivatives behave as physically homogeneous materials during sedimentation equilibrium runs in 6 m guanidine hydrochloride. The weight average molecular weights of all three thyrotropins are approximately 25,000. No evidence was found for separation into peptide chains of smaller molecular size after disulfide bond cleavage. In the absence of a dissociating agent bovine TSH exhibited concentration-dependent aggregation. End-group analyses were in agreement with the above and showed phenylalanine to be the major amino-terminal residue in both bovine and porcine thyrotropins. In human TSH, phenylalanine and valine were present in equal proportions. In addition, 0.1 to 0.2 moles of amino-terminal aspartic acid per mole of hormone was found in each case. The carboxyl-terminal sequences of bovine and human TSH are most probably -His-Tyr-Lys-Ser-Tyr-COOH; that of porcine TSH, -His-Tyr-Lys-Tyr-Ser-COOH. About 0.2 moles of methionine and leucine which could not be accommodated in the above sequences were also found at or near the carboxyl-termini of bovine and human TSH respectively. The amino acid and carbohydrate compositions of human and porcine TSH are compared with those of bovine TSH and purified human and bovine luteinizing hormones.