title: X-ray diffraction studies of enkephalins. Crystal structure of [(4'-bromo) Phe4,Leu5]enkephalin.
abstract: In order to investigate the structure-activity relationship of [Leu5]- and [Met5]enkephalins, [(4'-bromo)Phe4, Leu5]-, [(4'-bromo)Phe4, Met5]- and [Met5] enkephalins were synthesized and crystallized. The crystal structure of [(4'-bromo) Phe4, Leu5]- enkephalin was determined by X-ray diffraction method using the heavy atom method and refined to R = 0.092 by the least-squares method. The molecule in this crystal took essentially the same type I' beta-turn conformation found in [Leu5]enkephalin [Smith & Griffin (1978) Science 199, 1214-1216). On the other hand, the preliminary three-dimensional Patterson analyses showed that the most probable conformations of [(4'-bromo)Phe4,Met5]- and [Met5]enkephalins are both the dimeric extended forms. Based on these insights, the biologically active conformation of enkephalin was discussed in relation to the mu- and delta-receptors.
mesh_terms: D003460:Crystallization; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; C041081:enkephalin-Leu, 4'-bromo-Phe(4)-; C041080:enkephalin-Met, 4'-bromo-Phe(4)-