Conformational features responsible for binding of cyclic analogues of enkephalin to opioid receptors. I, Low-energy peptide backbone conformers of analogues containing Phe

Low-energy peptide backbone conformers were found by means of energy calculation for several cyclic analogues of enkephalin in an attempt to assess models for receptor-bound conformations for opioid receptors of the mu - and delta -types. The low-energy conformers obtained for these analogues were in good agreement with the results of calculations by other authors and with experimental evidence. All of the analogues contain a Phe residue in position 4 of the peptide chain which facilitates the eventual search for geometrical similarity between the low-energy backbone conformers of different analogues in question.