Characterization of solubilized human and rat brain beta-endorphin-receptor complex

Opioid receptors have been solubilized from human striatal and rat whole-brain membranes by use of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Tritiated human beta-endorphin (3H-beta h-EP) binding revealed high-affinity competition by morphine, naloxone, and various beta-EP analogues, suggesting predominantly mu-type binding. Lack of high-affinity competition by (+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneaceta mide methanesulfonate (U50-488, Upjohn) indicated that kappa sites were not labeled by 3H-beta h-EP under these conditions. Affinities were similar in both soluble and membrane preparations except for [Met]enkephalin, which appears to be rapidly degraded by the solubilized extract. Size differences between human and rat solubilized 3H-beta h-EP-receptor complexes were revealed by exclusion chromatography.