Conformational preferences and binding to neurophysins of oxytocin analogs with sarcosine or N‐methylalanine in position 7

Abstract
The 600 MHz proton NMR spectra of (sarcosyl7)-oxytocin and (N-methylalanyl7) oxytocin in 2H2O solution were recorded and completely assigned. In each case the spectrum indicates the presence of 2 slowly interconverting conformers, which are the cis-trans isomers about the peptide bond between residues 6 and 7. The trans isomer is energetically favored in both cases. When neurophysin is added to a solution of (N-methylalanyl7) oxytocin or (sacrosyl7)-oxytocin at pH 3.0, the proportion of minor conformer remains constant, indicating that the cis and trans conformers are equally tightly bound to the protein.