β-ENDORPHIN: SYNTHESIS AND RADIORECEPTOR BINDING ACTIVITY OF βh-ENDORPHIN-(1-27) AND ITS ANALOGS

β h ‐Endorphin‐(1–27) (I), [Ac‐Tyr 1 ]‐β h ‐endorphin‐(1–27) (II), [Gln 8 ]‐β h ‐endor‐phin‐(1–27) (III), and [Ac‐Tyr 1 , Gln 8 ]‐β h ‐endorphin‐(1–27) (IV) were synthe sized by the solid‐phase method. The binding potency of I‐IV to rat brain membrane preparations was measured by radioreceptor binding assay. The relative potencies were: β h ‐endorphin, 100; I, 30; II, 0.04; III, 90; IV, 0.07.