Displacement Reactions Employing Heterologous Tracer Ligands in Peptide Receptor Studies: A Review

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Abstract
Heterologous tracer ligands used in displacement studies with peptide-receptor systems may become unsuitable to these aims for several reasons. (1) The forms of binding isotherms for the tracer and for the ligand under investigation are different. The Schild plot and similar schemes are then not applicable. Possible modifications of the computational methods are indicated. (2) The rate of dissociation from the receptor is slowed, until almost irreversible. In such cases, there is no chance for displacement studies. (3) Large discrepancy in rate constants, or dramatically different distribution coefficients between binding system and water, for the two ligands mimic irreversible binding to receptors in a pharmacological experiment. Adjustment of ligand concentrations (control of association rate) may help in some instances.