Secondary structure of polypeptide hormones of the anterior lobe of the pituitary gland

Abstract

Abstract The specific secondary structure of a number of polypeptide hormones of the pituitary gland anterior lobe and their fragments were studied by CD in the peptide bond absorption region and by ir spectroscopy. The state of objects was examined in solvents of different polarity over a wide temperature range as well as in the solid state at different relative humidities. The predominant conformational state of a number of hormones in aqueous solution is shown to represent a left‐handed helix of the poly( L ‐proline) II type. The reversible melting process of the left‐handed helical conformation when heated in an aqueous solution appears to be noncooperative. Lowering the temperature stabilizes the left‐handed structure. The transition mode of the left‐handed form to the α‐, and the β‐forms on changing the solvent conditions was also studied. Contributions of peptide chromophores and of the aromatic amino acid side‐group chromophores with CD bands in the region under study were determined by analysis of CD spectra. The data obtained allow correlating the conformation of separate fragments in the hormone chain with functional activity.