Conformational studies of the pentapeptides with weak adrenocorticotropin (ACTH) activities by means of nuclear magnetic resonance spectroscopy
✍ Scribed by Naoki Higuchi; Yoshimasa Kyogoku; Haruaki Yajima
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1981
- Tongue
- English
- Weight
- 461 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0006-3525
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
The conformations of a pentapeptide L‐His‐L‐Arg‐L‐Trp‐Gly with weak adrenocorticotropin (ACTH) activity and its analogs, where each L‐amino acid residue is substituted by D‐residue, were investigated by means of proton and carbon‐13 nmr spectroscopy on their DMSO‐d~6~ solutions. The spectra indicated the presence of slowly exchangeable conformation isomers for D‐Phe and D‐Arg analogs, due to steric hindrance around the arginine residue. The activation energy of the hindered rotation of the arginine side chain was estimated to be more than 19 ∼ 20 kcal/mol. Spin‐lattice relaxation times of carbon‐13 nuclei also indicated slow segmental motion of the arginine side chain of the D analogs. An effect on proton chemical shifts by intermolecular electrostatic interaction between the arginine side chain and the C terminal carboxylic residue was observed. We did not observe, however, a direct correlation between pentapeptide activity and molecular conformation at this stage of the experiments.