Proline‐containing β‐turns in peptides and proteins. II. Physicochemical studies on tripeptides with the Pro‐Gly sequence

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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.