title: Opioid and non-opioid binding of beta-endorphin to bovine adrenal medullary membranes.
abstract: Binding of human beta-endorphin (beta h-EP) to bovine adrenal medullary membranes was characterized using [125I]Tyr27-beta h-EP [( 125I]beta h-EP) as a primary ligand. The specific binding of [125I]beta h-EP was time-dependent, saturable and stereospecific. Analysis of a saturation isotherm revealed two apparent classes of specific binding sites with dissociation constants of 2.4 and 34 nM. The extent of maximum inhibition of specific [125I]beta h-EP binding by either levorphanol, morphine, naloxone, dynorphin A (1-13) or D-Ala2-D-Leu5-enkephalin was similar to each other and remained partial (60-70%). Levorphanol eliminated the high affinity component but showed no effect on the low affinity component of [125I]beta h-EP binding. beta h-EP(1-31) displaced completely the [125I]beta h-EP binding. However, beta h-EP(1-23) only partially (approximately 80%) inhibited the [125I]beta h-EP binding. beta h-EP(6-31) showed inhibitory activity on [125I]beta h-EP binding. These results suggest that [125I]beta h-EP binding to bovine adrenal medullary membranes consists of a high affinity opioid-sensitive component and a low affinity non-opioid component. The non-opioid component of [125I]beta h-EP binding may be related to COOH-terminal of the beta h-EP molecule.
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002417:Cattle; D004723:Endorphins / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D007981:Levorphanol / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D007981:Levorphanol; D001615:beta-Endorphin