The three-dimensional similarity between a dimeric antiparallel extended structure and a beta-turn folded form of enkephalin.

The three-dimensional similarity between two fundamental conformations, a dimeric antiparallel extended structure and a type I' beta-turn folded form, of enkephalin was examined by computer graphic and empirical energy calculation methods. By the rotation of Tyr and Phe side chains, one half of the former structure could mimic the three-dimensional form of the latter without a large loss of conformational energy. This result provides a new idea for considering the conformation of enkephalin suitable for the multiple opioid receptors. The active conformation of enkephalin for mu- and delta-opioid receptors is discussed in the light of the present study.