| 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. |
