Sense of the Helix in Poly-L-tyrosine

Abstract

THE anomalous rotatory dispersion curves for many synthetic poly-α-amino-acids in the helical conformation have been adequately interpreted by the equation proposed by Moffitt¹. The constant, b₀, in this equation has been used as a measure of helix content in polypeptides and proteins². The sign of b₀ has been taken to signify the sense of the helix^1,3–6. A value of approximately − 630 has been found for the helical conformation of poly-L-glutamic acid^1a, poly-γ-benzyl-L-glutamate^1,4 and for poly-L-alanine⁷; the latter has been shown to exist as a right-handed helix⁸. The first reported positive b₀ value was that found for poly-L-tyrosine⁷, and it was suggested that the unusual sign of b₀ is a consequence of a strong chromophoric group near the β-carbon. Other positive b₀ values have since been reported for poly-β-benzyl-L-aspartate³, poly-1-benzyl-L-histidine⁹ and poly-L-tryptophan¹⁰. It was suggested that the positive b₀ value of poly-β-benzyl-L-aspartate was due to a different sense of twist³ than that found for poly-γ-benzyl-L-glutamate. Proof of this hypothesis followed shortly^4,11.