Identification of the serotonin‐S2 receptor ligand binding site by photoaffinity labelling with 7‐azido‐8‐[125I]ketanserin ([125I]AZIK)

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Abstract
7-Azido-8-[125I]ketanserin ([125I]AZIK) was characterized as a potent photoaffinity probe for serotonin-S2 receptors. In reversible binding experiments, [125I]AZIK bound with high affinity (Kd = 0.69 nM) to rat frontal cortex membranes. When incubation with [125I]AZIK was followed by UV irradiation, the binding was found to be irreversible. Protection experiments with various drugs demonstrated the serotonin-S2 nature of the photoaffinity labelling. SDS-polyacrylamide gel electrophoresis of the photolabelled membranes allowed one to identify the serotonin-S2 receptor ligand binding site as a single polypeptide with a molecular mass of approx. 67500 Da. [125I]AZIK will be a valuable tool for the elucidation of the serotonin-S2 receptor structure