Structural Studies on Polypeptide Hormones

The rotational characteristics of polypeptides containing a tryptophanyl residue have been evaluated by polarization of fluorescence measurements in concentrated glycerol solutions. A curve has been obtained showing the dependence of relaxation time on chain size based on the behavior of two series of peptides, i.e. Glyx−Trp−Glyy and adrenocorticotropic hormone and some of its fragments. If these molecules are structureless polypeptides then it can be ascertained, from the relaxation times of molecules with unknown structures, whether the indole group possesses unrestricted or restricted rotational freedom. In the latter case, one can conclude that there exist some elements of structure in the molecule. Several hormones and polypeptides (gastrin, glucagon, parathyroid hormone, and mellitin) and some of their fragments have been evaluated for tertiary interactions by this procedure.