The α-βTransformation in a Polypeptide

Abstract

IN an earlier communication¹ we gave evidence for the presence of an α-structure in fibres of two synthetic polypeptides—a copolymer of L–glutamic γ-methyl ester with DLβ–phenylalanine (A), and poly-DL-phenylalanine (B). These fibres were prepared from solutions in m-cresol by extrusion into non-solvents. By this method oriented fibres with an α-protein type of structure were prepared, and we suggested that the fold which best fits the crystallographic and infra-red data is that first postulated by Huggins² for α-keratin, and later by Ambrose and Hanby³ to explain the parallel dichroism of the N—H stretching vibrations in poly-L-glutamic γ-methyl ester. (It is interesting to note that the 5·28 A. polar arc of fibre B is weak and diffuse, whereas that of A is strong and well defined. Qualitatively, therefore, the X-ray results are not inconsistent with the presence of a two-fold screw axis in a symmetrical polymer molecule ; see Astbury⁵.)