title: Identification of the D2-dopamine receptor binding subunit in several mammalian tissues and species by photoaffinity labeling.
abstract: Photoaffinity labeling of the D2-dopamine receptor in plasma membrane preparations of various tissues from several mammalian species was performed using the recently developed D2-dopaminergic antagonist probe [125I]N-(p-azidophenethyl)spiperone ([125I]N3-NAPS). In tissues containing D2-receptors such as the corpus striatum from rat, dog, calf, hamster, guinea pig, and rabbit as well as the anterior pituitary of rat, bovine, and hamster, the probe covalently labels a peptide of Mr = 94,000. Specificity of the labeling is typically D2-dopaminergic in character. The covalent labeling is blocked by (+)-butaclamol but not by the inactive (-)isomer. Agonists block incorporation with the order of potency: N-n-propylnorapomorphine greater than apomorphine greater than dopamine. The D2-selective antagonist spiperone blocks labeling of the Mr = 94,000 peptide whereas the D1-selective antagonist SCH-23390 is ineffective. Thus, these results indicate that the ligand binding subunit of the D2-dopamine receptor resides on a Mr = 94,000 peptide in these various tissues from several species. Under conditions where proteolysis is not stringently controlled, peptides of lower Mr (32-38,000) are labeled at the expense of the Mr = 94,000 peptide. The most efficient protease inhibitor tested in these systems was EDTA, suggesting that the generation of these lower Mr receptor fragments might be the result of a metal-dependent proteolysis in the membrane preparations. In the rat neurointermediate lobe, a tissue containing D2-receptors, [125I]N3-NAPS specifically labels a major peptide of Mr approximately equal to 120,000 in addition to the Mr = 94,000 peptide.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000345:Affinity Labels; D000818:Animals; D001386:Azides; D002417:Cattle; D003342:Corpus Striatum / Q000378:metabolism; D006224:Cricetinae; D004285:Dogs; D006168:Guinea Pigs; D008027:Light; D008297:Male; D008647:Mesocricetus; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000378:metabolism*; D017448:Receptors, Dopamine D2; D012160:Retina / Q000378:metabolism; D013134:Spiperone / Q000031:analogs & derivatives
chemical_list: D000345:Affinity Labels; D001386:Azides; D011480:Protease Inhibitors; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D013134:Spiperone; C044567:N-(4-azido-3-iodophenethyl)spiperone