The structure of thyrotropin-releasing hormone of porcine origin has been systematically investigated by a series of degradation reactions. N-Bromosuccinimide cleavage followed by the dansyl reaction and Edman degradation revealed a C-terminal prolyl end group, preceded by the histidyl moiety. Mild alkaline hydrolysis and subsequent dansyl reaction proved the N-terminal residue to be (pyro)-glutamic acid. The fragmentation patterns in the mass spectra of free as well as permethylated thyrotropin-releasing hormone supported the Glu-His-Pro sequence for the constituent amino acids. Methanolysis and hydrazinolysis indicated that an acyl substituent is unlikely to be present at the N-terminus. The possibility of substituents at the N- or C-terminus was also investigated by partial acid hydrolysis, followed by separation of the products by thin-layer chromatography and their spectroscopic characterization. The results obtained support L-(pyro)Glu-L-His-L-Pro-NH2 as being the structure of the porcine thyrotropin-releasing hormone.
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