| Abstract: | Amino acids are known to differ in their individual preferences for each of the four positions of the β-turn conformation formed by tetrapeptide segments. Proline and glycine show relatively high preferences for positions 2 and 3, respectively, of the β-turn. Using tripeptides of the type N-acetyl-Pro-Gly-X-OH, where X = Gly, Ala, Leu, Ile, and Phe, we have sought to study the influence of the 4th residue X on the stability of the β-turn conformation in these tripeptides. Our nmr and CD results show that the β-turn stability is quite significantly governed by the nature of the amino acid residue at this position in the following order: Leu > Ala > Ile, Gly > Phe. |
