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. Author manuscript; available in PMC: 2014 Oct 27.
Published in final edited form as: J Am Chem Soc. 2013 Mar 11;135(11):4333–4363. doi: 10.1021/ja3109664

Figure 1.

Figure 1

Proline conformational equilibria. (a) Cis-trans isomerism of the prolyl amide bond. In proteins, 95% of prolyl amide bonds are trans, 5% are cis. The trans and cis amide bond are in slow exchange on the NMR timescale, so the relative populations (Ktrans/cis = [peptide with trans amide bond]/[peptide with cis amide bond]) are determined via quantification of their distinct NMR resonances. (b) Exo and endo ring puckers of proline. Exo and endo ring puckers are in rapid equilibrium. (c) Definition of main chain torsion angles in proline.