The binding of Tb-DeltI to CHO/MYChDOR -cells. A. Tb-DeltI can displace 3H-diprenorphine with similar affinity as unlabeled DeltI. In the competitive binding experiment 0.1 nM – 10 μM Tb-labeled DeltI or native DeltI was used to displace 6.86 nM3H-diprenorphine from the CHO/MYChDOR cell membranes. Tb-DeltI displaced the radioligand with a similar affinity as the unlabeled native DeltI. The solid line (curve fit) and the crosses represents the competitive binding for DeltI; the dashed line and the open circles for Tb-DeltI. The data is presented as the specific binding (SB) relative to the total binding (TB). The specific binding depicts the radioligand binding that can be displaced by the competing ligand (DeltI or Tb-DeltI). B. Tb-DeltI shows specific, saturable binding to DOR binding sites. The nonspecific binding of Tb-DeltI to CHO/MYChDOR -cells was determined in the presence of 1 μM DeltI. The binding of Tb-DeltI was saturable at a nanomolar range. The data is presented as the specific binding (SB) relative to the total binding (TB). The specific binding depicts the binding of Tb-DeltI that can be displaced by the unlabeled ligand.