Immuno-photoaffinity labeling of the D2-dopamine receptor

Azido-haloperidol was synthesized and applied as a photoaffinity ligand for the D2-dopamine receptor. In bovine striatal membranes, azido-haloperidol bound reversibly to the receptor (KD = 15 nM), and when exposed to light, it bound to the receptor irreversibly. This irreversible inactivation was prevented by the dopaminergic agonist N-propylnorapomorphine or the dopaminergic antagonists haloperidol and (+)-butaclamol. The photoaffinity labeled D2-receptor was probed with anti-haloperidol antibodies following gel electrophoresis and transfer to nitrocellulose. A major polypeptide of 94 kDa reacted with the anti-haloperidol antibodies. This polypeptide band was not observed when the photoaffinity labeling was performed in the presence of (+)-butaclamol or spiperone.