title: Binding of 3H-beta-endorphin in rat brain.
abstract: The binding of 3H-beta-endorphin to rat brain homogenates, reported by several other laboratories, has suggested unique selective beta-endorphin binding sites. We now present additional evidence supporting the concept of distinct beta-endorphin binding (epsilon) sites in rat brain. In competitive displacement studies, 3H-beta-endorphin was inhibited far better by unlabeled beta-endorphin than a variety of opiates and enkephalins. Conversely, beta-endorphin inhibited the binding of a series of 3H-labeled ligands, including dihydromorphine, ethylketocyclazocine, SKF 10,047, naloxone and D-ala2-D-leu5-enkephalin, far less potently than their corresponding unlabeled drug. Other differences were also found. Compared to 3H-dihydromorphine and 3H-D-ala2-D-leu5-enkephalin binding, 3H-beta-endorphin binding was far less sensitive to the reagent N-ethylmaleimide and more sensitive to the proteolytic enzyme trypsin. The regional distribution for 3H-beta-endorphin binding was also distinct from other 3H-ligands tested. This evidence supports the concept of a distinct binding site for beta-endorphin which does not correspond to the previously defined opioid binding sites.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D004723:Endorphins / Q000378:metabolism*; D066298:In Vitro Techniques; D051381:Rats; D011957:Receptors, Opioid / Q000032:analysis; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid; D001615:beta-Endorphin