Figure 2.

Competitive inhibition of ¹²⁵I-exendin(9–39) binding by peptide agonists for Ala mutants of the hGLP-1R N-terminal ECD and TM1 and linker region. Binding affinity data are expressed as a percentage of measured bound versus bound in the absence of peptide, each corrected for nonspecific binding (measured in the presence of 1 μm unlabeled exendin(9–39)). Inhibition curves of WT and mutant receptors were stimulated by GLP-1(7–36)NH₂ (upper panels), exendin-4 (middle panels), or oxyntomodulin (lower panels) in CHO–Flp-In cells stably expressed WT or mutant receptors. Data were fitted with a three-parameter logistic equation. All values are means ± S.E. of four to six independent experiments, conducted in duplicate.