Conformational Study of Sequential Polypeptides of L-Alanine and D-Alanine

Abstract

Infrared spectra in the 700-200 em -J and in the amide I and II regions were measured for poly(L-Ala-L-Ala-n-Ala), poly(L-Ala-L-Ala-n-Ala-n-Ala), poly(L-Ala-L-Ala-L-Ala-D-Ala), and poly(L-Ala-n-Ala-L-Ala-n-Ala) with different degrees of polymerization. The spectra showed that the films cast from aqueous solutions ofpoly(L-Ala-L-Aia-n-Aia), poly(L-Aia-L-Ala-D-Ala-n-Ala), and poly(L-Aia-L-Ala-L-Aia-n-Aia) take disordered conformations containing appreciable amounts ofL-alanine residues with local right-handed a-helix-like structures and then-alanine residues with local left-handed a-helix-like structures. The disordered conformations were converted to the extended {J-form when treated with ethanol. The latter conformation is also found in waterinsoluble portions of poly(L-Ala-L-Aia-n-Ala-n-Aia) and poly(L-Ala-L-Ala-L-Aia-n-Ala). On the other hand, poly(L-Ala-n-Ala-L-Aia-n-Aia) has a conformation different from those taken on other sequential polypeptides studied in this paper. The above findings were confirmed also by the measurement of the Raman spectra of poly(L-Ala-L-Ala-n-Aia) and poly(L-Ala-n-Ala-L-Aia-D-Ala).

Conformational Study of Solid Polypeptides by 1H Combined Rotation and Multiple Pulse Spectroscopy NMR. 2. Amide Proton Chemical Shift

“…Materials. The l -alanine pentapeptide n -butylamide, H-[Ala] 5 -NHBu, was synthesized by the activated ester method , and other polypeptide samples of natural abundance, [Ala] n -5, [Leu] n -1, and [Leu] n -2, were synthesized by the N -carboxy α-amino acid anhydride (NCA) method , in our laboratory. The fully 15 N-labeled homopolypeptides such as [Ala*] n (99 at.…”