Ligand depletion shifts the binding curve rightward and obscures distinct features of the two binding sites. A. Fractional occupancy of total specific binding sites is shown at various concentrations of R1T. Increasing total binding sites increases ligand depletion, which shifts the total binding curve rightward. Ligand depletion also distorts the two sigmoidal features arising from binding to the high and low affinity sites. B. The fractional occupancies of high and low affinity sites are shown separately. The legend in A applies to B. Fractional occupancies of the low affinity site are clustered in the lower right corner of the plot. Only lines from R1T values of 13 and 130 nM are distinct for the low affinity site. The leftmost line from the low affinity site arises from overlap of the lines from the first five concentrations of binding sites. Binding was calculated with two sites modelfree.
Person and Wells BMC Biophysics 2011 4:19 doi:10.1186/2046-1682-4-19