Figure 5. Representative competitive binding assay at the MC4R.

A. Increasing concentrations of the MSH-Deltorphin heterobivalent ligand were added to CHO/MC4R/δOR cells in the presence of 10 nM Eu-DTPA-NDP-α-MSH and the absence (dimer) and presence (monomer) of competing naloxone. For dimer binding (absence of naloxone), the IC₅₀ = 3.2 nM with R² = 0.83; for monomer binding (presence of naloxone), the IC₅₀ = 134.0 nM with R² = 0.93. B. Increasing concentrations of the MSH-CCK heterobivalent ligand were added to cells in the presence of 10 nM Eu-DTPA-NDP-α-MSH. For dimer binding, Hek293/CCK2R/MC4R cells were used and for monomer binding, Hek293/MC4R cells were used. For dimer binding, the IC₅₀ = 4.5 nM with R² = 0.88; for monomer binding, the IC₅₀ = 349.5 nM with R² = 0.96.