A functionalized derivative of the α2-selective antagonist rauwolscine formed the basis for a photoaffinity adduct that has allowed identification of the hormone-binding subunit of the brain α2-adrenergic receptor protein. Rauwolscine carboxylate underwent reaction with 4-N-t-butyloxycarbonylaminoaniline, leading to the synthesis of rauwolscine 4-aminophenyl carboxamide (Rau-AmPC). Rau-AmPC was radioiodinated and converted to the arylazide derivative, 17α-hydroxy-20α-yohimban-16β-[N-(4-azido-3-[125I]iodo) phenyl] carboxamide (125I-Rau-AzPC), via a diazonium salt intermediate. The characterization of 125I-Rau-AzPC as a photolabile probe employed α2-adrenergic receptors, which were first solubilized from porcine brain membranes and partially purified by affinity chromatography utilizing a yohimbine-agarose affinity matrix. In the partially purified receptor preparation incubated with 125I-Rau-AzPC, photolysis resulted in covalent labeling of a major (M(r), 62,000) peptide as determined by NaDodSO4/PAGE and autogradiography. Labeling of this peptide was inhibited by the α2-selective antagonist, yohimbine, and the non-subtype-selective α-antagonist, phentolamine, but not by the α1-antagonist, prazosin, or the β-receptor antagonist, (-)-alprenolol. The α-adrenergic agonist epinephrine also inhibited labeling in a stereoselective manner. These data indicate that the photolabeled M(r) 62,000 peptide is the hormone-binding subunit of the α2-adrenergic receptor protein. The availability of this radioiodinated photoaffinity probe for the α2-adrenergic receptor should facilitate further structural and biophysical characterization of the receptor protein.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 1986|
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