SynopsisThe infrared amide I band of collagens (rat and cod skin) and related compounds (polyproline, polyglycine, and polytripeptides) was studied. Assignment of amide I-band components for polyproline I1 and polytripeptides (Gly-Pro-Pro), and (Gly-Pro-Gly),, in the solid state and water solution was made. Three amide I components observed in the polypeptide spectra were attributed to three different peptide CO groups in each triplet. On the basis of this assignment, the interpretation of the amide I multicomponent structure in collagen and isomorphous oligo-and polypeptides was attempted. The ordering of intra-and intermolecular hydrogen bonds involving peptide CO groups in collagen and related compounds was discussed.

The ir amide bands of the triple-helical polytripeptides and collagens upon hydration of films are investigated. On the basis of our assignment of the amide I components, the formation of hydrogen bonds between the peptide backbone and structural water is studied. The C1O1--HOH hydrogen bonds are found more ordered than the C3O3--HOH hydrogen bonds. The specific incorporation of water in the triple helix is followed by multistep conformational changes and by increasing of the interpeptide hydrogen-bond strength. The formation of the polypeptide hydrate structure depending on the amino acid composition and the chain length is examined.

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SynopsisThe 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) I1 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 a-, and the p-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. INTRODUCTIONTo polypeptide hormones of the anterior lobe of the pituitary gland are related a number of small peptides (from 13 to 93 amino acid residues) exhibiting partially overlapping activity. Of these the conformations of adrenocorticotropic hormone (ACTH) and sheep 0-lipotropic hormone (P-LPH) in solution were studied. It was shown that in trifluoroethanol the greater part of the ACTH molecule assumes an a-helical conformation; however, no final conclusions have been made about the structure of the hormone in aqueous solution.'O2 The far-uv CD study of sheep P-LPH shows that methanol, sodium dodecyl sulfate, and dioxane promote the formation of a-helical structure in the ~eptide.3,~ Intrinsic viscosities and sedimentation coefficients of this hormone suggest that the molecule is not compact and g l~b u l a r .~ Our preliminary spectral studies of the conformation of polypeptide hormones of the pituitary gland in solution and as film^^,^ demonstrate the presence of regular structures that alter with the change in conditions of the medium. The present work has been under-* Present address: Cancer Centre, USSR Academy of Medical Sciences, Moscow, USSR. Biopolymers, Vol. 23,5-22 (1984) taken to study in detail the structural forms of polypeptide hormones (and their fragments) of the anterior lobe of the pituitary gland in solution and as films. Their transformations with changing conditions of the medium and possible functional consequences are also examined. METHODS AND MATERIALSThe CD spectra in the peptide bond absorption region were measured on a Mark I11 Jobin-Yvon dichrograph at 20°C. A cryostat accessory for the Roussel-Jouan CD-185 dichrograph allowed us to alter temperatures in the cell from -195 to 39°C. Heating was accomplished using an ultrathermostat. The sample was kept for not less than 30 min at each temperature. CD was expressed in A6 molar units (l/cm mol pep...