The configuration of the polypeptide chain in small peptides such as gramicidin S

Abstract

The infra-red spectra of a number of small peptides have been measured and it is concluded that for a degree of polymerization greater than two the absorption bands of the peptide —NH—CO— group are reasonably characteristic. The spectra of various crystalline derivatives of gramicidin S, a cyclic decapeptide, have been examined. Measurements with polarized radiation indicate considerable dichroism which is very similar to that shown by folded synthetic polypeptides and α -keratin. It is possible to construct a model, using a fold with hydrogen-bonded rings, which appears to satisfy the intra-red data and also to represent a stable configuration for the polypeptide chain.