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Conformational studies of the pentapeptides with weak adrenocorticotropin (ACTH) activities by means of nuclear magnetic resonance spectroscopy
Author(s) -
Higuchi Naoki,
Kyogoku Yoshimasa,
Yajima Haruaki
Publication year - 1981
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1981.360201013
Subject(s) - chemistry , pentapeptide repeat , steric effects , arginine , residue (chemistry) , side chain , nuclear magnetic resonance spectroscopy , stereochemistry , nuclear overhauser effect , intermolecular force , crystallography , spectroscopy , chemical shift , amino acid , organic chemistry , peptide , molecule , biochemistry , polymer , physics , quantum mechanics
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.