Conformations of Sequential Polypeptides Containing l-Alanyl and Glycyl Residues

The conformations of four polypeptides containing ordered sequences of l-alanyl(A) and glycyl (G) residues, (A)n, (A3G)n, (A2G)n, and (AG2)n, are investigated in solution. The optical rotatory dispersion and infrared spectra showed that all the polymers assume both an α-helical conformation and a β-conformation in solution. The stability of the α-helix decreases in the oder: (A)n, (A2G)n, (A3G)n, and (AG2)n; this may be explained in terms of the interaction between methyl groups of l-alanyl residues regularly arranged on the surface of the α-helix.