Figure 1.

Competition of binding of the antagonist ¹²⁵I-Tyr-ME to membranes pretreated with agonist and extracted with 6 M urea. The relative potency of different Bn receptor agonists (Bn, ▴; GRP, ▵; NMB, ▪) and a GRPr-specific antagonist (ME, •) were compared by competition binding to membranes pretreated with agonist before extraction with 6 M urea. The binding reaction was initiated by adding 25 μl of membranes (0.41 μg of protein) to 25 μl of binding solution containing ¹²⁵I-Tyr-ME (87 pM final concentration) and various concentrations of unlabeled competitor. Binding proceeded for 45 min at 30°C, and bound radioligand was measured as described.