Figure 2.

Simulated competition binding curves using two different concentrations of labelled ligand. Typical competition binding curves were generated in GraphPad Prism. The one site competition equation (which incorporates the Cheng–Prusoff correction) was used with 10 nM and 500 nM of the labelled ligand, which had a K_d of 10 nM. The IC₅₀ values for these curves were 20 nM and 500 nM, respectively. Using the Cheng–Prusoff equation, this gives a K_i of 10 nM for the unlabelled ligand under both conditions. This demonstrates the differences in the concentration–response curves and IC₅₀ values that can be obtained if high concentrations of the labelled ligand are used.