Displacement binding radioligand concentration

Figure 6 Displacement binding. Radioligand and cold ligand compete for receptor binding. A single radioligand concentration is displaced by increasing concentrations of competitive ligand.

The ( )-enantiomer of 5 shows low relative affinity (Ki = 605 nM) for the nAChR [3//]nicotine binding site, whereas the (+)-enantiomer fails to displace the radioligand even at 10 o,M concentrations. ... 

Radioligand (final concentration 10—lOOpM for I-chemokines and 50-500 pM for I-nanobodies), 25 pl/weU, is added to the plate. A fixed concentration of radioligand is used in displacement binding... 

Since the kinetics of receptor binding, and therefore the sensitivity of a radioreceptor assay, may vary with tissue concentration or incubation conditions, it is prudent to calculate a standard curve for the displacement of radioligand during each experiment. To this end, the amount of radioligand bound in the presence and absence of various concentrations... 

FIGURE 3.3 Displacement of prebound radioligand [A ] by non-radioactive concentrations of [A]. Curve for a= 1 denotes no cooperativity in binding (i.e., formation of the receptor dimer does not lead to a change in the affinity of the receptor for either [A] or [A ]). The curve a= 10 indicates a system whereby formation of the receptor dimer leads to a tenfold increase in the affinity for both [A ] and [A], In this case, it can be seen that addition on the nonradioactive ligand [A] actually leads to an increase in the amount of radioligand [A ] bound before a decrease at higher concentrations of [A], For this simulation [A ]/Kd = 0.1. 

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