(E–J) Competition AlphaScreen assays with purified receptor ECD heterodimer proteins and the indicated competitor “swap” peptides. (E)–(G) are for the MBP-RAMP1-(GSA)3-CLR-H6 protein with biotin-CGRP (100 nM each) and (H)–(J) are for the MBP-RAMP2[L106R]-(GSA)3-CLR-H6 protein with biotin-AM (100 nM each). The binding data are representative of at least three independent experiments each performed in duplicate. The error bars represent the SEM of the experiment. Determinable pIC50 values were as follows: (F), CGRPmut 6.79 ± 0.10 and CGRPmut [F37Y] 6.24 ± 0.09; (G), CGRP(8-37) 5.01 ± 0.04; (H), AM(22-52) 4.92 ± 0.16; (I), AM(22-52) 4.84 ± 0.09 and CGRPmut [F37Y] 4.79 ± 0.07; (J), AM(37-52) 5.00 ± 0.11.