Raman Spectra and Conformations of Copolypeptides Containing Glycine, L-Alanine, and L-Phenylalanine Residues

Abstract

Raman spectra were measured for copolymers of L-alanine and glycine and those of L-alanine and L-phenylalanine. The L-alanine-glycine copolypeptides with a glycine residue content of 3—21 mol% take the α-helical conformation. On incorporation of the glycine residue at more than 30%, the backbone structure changes partly from the α-helix to the β-form. The L-alanine–L-phenylalanine copolypeptides with the L-phenylalanine content of 12—92% take the α-helical structure. The following Raman bands reflect the α-helix or the β-form structure of the component amino acid residues; the bands near 1308, 1108, 530 and 378 cm−1 are characteristic of the L-alanine residue with the α-helical structure, the band near 1094 cm−1 of the L-alanine resdue with the β-form, the band in the 470—480 cm−1 region of the L-phenylalanine residue with the α-helix, and the band near 490 cm−1 of the L-phenylalanine with the β-form.