Receptor binding affinity is the quantitative measure of the strength and duration of the molecular attraction between a signaling molecule, or ligand, and its specific receptor site. A high binding affinity indicates that the ligand can bind effectively even at low concentrations, while a low affinity requires a higher concentration to achieve the same degree of receptor occupancy. This pharmacological parameter is a primary determinant of a hormone’s potency and its ability to elicit a biological response at the target cell.
Origin
This is a core concept in pharmacology and biochemistry, combining “receptor,” the binding target, with “binding affinity,” the measure of the thermodynamic favorability of the interaction. It is often quantified by the dissociation constant (Kd). In endocrinology, the affinity of a hormone for its receptor is a critical factor in understanding hormonal action and the mechanism of synthetic analogs.
Mechanism
The affinity is governed by the non-covalent intermolecular forces, including hydrogen bonds, ionic interactions, and van der Waals forces, that form between the ligand and the amino acid residues within the receptor’s binding pocket. A higher number and more optimal geometry of these interactions result in a lower dissociation rate and thus a higher affinity. This molecular precision ensures that the correct hormone acts selectively on its intended target cells, maintaining the fidelity of the endocrine signaling network.
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