Hydrogen-1 and carbon-13 nuclear magnetic resonance conformational studies of the His-Pro peptide bond: conformational behavior of TRH†
- 1 November 1983
- journal article
- research article
- Published by Wiley in International Journal of Peptide and Protein Research
- Vol. 22 (5) , 582-589
- https://doi.org/10.1111/j.1399-3011.1983.tb02132.x
Abstract
Cis/trans isomerism of the His‐Pro peptide bond provides a convenient model for the effect of a slow conformational change which may have wider biological significance. Above the imidazole pK, His‐Pro is conformationally analogous to the (isosteric) peptide Phe‐Pro. Protonation of the imidazole sidechain is associated with a large decrease in the cis/trans ratio. Detailed 1H and 13C n.m.r. analysis suggests the importance of electrostatic/hydrogen bonding interactions between the charged imidazolium sidechain and the proline carboxyl as the basis for this effect. In contrast to a previous report, cis/trans isomerism in TRH is shown to be related to titration of the imidazole sidechain, exhibiting a pK of 6.1.Keywords
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