Optical properties of the polyglycine II helix

The circular dichroism spectrum obtained from a dilute aqueous solution of poly (ala‐gly‐gly) resembles that described for charged polypeptides such as the salt form of poly glutamic acid. A similar spectrum is found for films cast from aqueous solution where x‐ray studies reported elsewhere have indicated a poly‐glycinc II conformation. Evidence is presented for a heat induced poly‐glycine II to unordered state transition similar to that described for collagen. The interpretation of this, the first observation of the optical properties of a poly‐amino acid in the poly glycine II conformation, is further rationalized on the basis of spectra obtained from a number of polypeptides whose conformation approaches that of a 31 helix.