Optical Rotation and Configuration of Poly-L-Tyrosine

Abstract

IN a recent communication¹, Downie, Elliott and Hanby report that the optical rotatory dispersion of poly-L-tyrosine is unusual and, as a result, its configuration cannot be assigned by analogy with polypeptides having normal dispersion characteristics. However, they interpret their data, together with unspecified infra-red spectral and X-ray diffraction observations of films, as indicating that “it is more probable that in dilute solutions in pyridine, in dimethyl formamide, and in aqueous alkali, poly-L-tyrosine is in a random coil configuration”. Our study of this problem has led to somewhat different conclusions: that the configuration in pyridine and dimethyl formamide is that of the α-helix, whereas in alkaline solution the configuration is dependent on pH, indicative of the random-coil configuration. The basis of the configurational assignments will be published elsewhere in detail, but we wish to summarize them here and report the optical rotatory characteristics of the two forms.