Characterization of L-methionine in a peptide α-helix by far-infrared spectroscopy. Synthesis and examination of sequential polypeptides containing L-methionine

Abstract

Sequential polypeptides containing L-methionine, viz.(Met-Ala-Ala)_n, (Met-Met-Ala-Ala)_n, (Met-Met-Ala)_n, (Leu-Met-Leu)_n, (Leu-Met-Met-Leu)_n, and (Met-Met-Leu)_n, were synthesized by polycondensation of peptide ONSu esters with corresponding sequences of amino acids; the ONSu esters were prepared stepwise by the method for peptide synthesis using Nps-amino acids and dicyclohexylcarbodi-imide. α-Helical samples of all the polypeptides showed a common far-i.r. band at 409 cm^–1, the strength of which changed with the proportion of L-methionine residue in the polypeptides. Thus, this band was assigned to L-methionine in an α-helical polypeptide.