Figure 1
Polypeptide backbone and possible rotations. (a) Rotation around the peptide C—N bond is not possible because of the mesomeric equilibrium between two resonance structures. (b) As a consequence the dihedral angle ω may assume two values, yielding two conformations: cis (ω = 0°) and trans (ω = 180°). (c) The rotation around the N—Cα bond can be monitored by the dihedral angle Ci−1—N—Cα—C, which is named φ, while the rotation around the Cα—C bond can be measured by the dihedral angle N—Cα—C—Ni+1, which is termed ψ. |