SYNTHETIC ENKEPHALINS Addicting Properties and Conformational Studies in Solution

Publisher Website
Google Scholar
Abstract
The addicting properties of [Leu5]-enkephalin in mice are conserved in the L-Ser3 analog and lost both in the L-Ser2 analog and in all the L-Cha4 [cyclohexylalanine] derivatives of the above peptides. Fluorescence measurements in water show the presence of H-bonded tyrosyl OH groups in [Leu5]-enkephalin and in its L-Ser2 analog. The Phe4/Cha replacements do not influence these equilibria, but they affect the near UV dichroism of the H-bonded tyrosyl residues. In the peptide adsorption region in water solution, only [Leu5]-enkephalin and its Cha derivative show a positive dichroism towards high frequencies, which is maintained in 8 M urea. No clear relation is found between conformation(s) in solution and biological activity. A II'' .beta.-turn, with residues in positions 2 and 3 at the corners, is suggested for the conformation of enkephalin bound to the receptors involved in the bioassay here used.