Interaction of leucine enkephalin with (3H)naloxone binding in rat brain: Evidence for an opioid receptor complex

Abstract

We recently presented evidence that distinct morphine and enkephalin receptors coexist in an opioid receptor complex (Mol. Pharmacol. 21:548–557, 1982). In this paper, we present data which demonstrate that in the presence of sodium leucine enkephalin noncompetitively inhibits the binding of [³H]naloxone to a crude particulate fraction of rat brain. Since the binding site labeled by [³H]naloxone in the presence of sodium may be an alternate conformation of the morphine receptor, these data provide further evidence that morphine and enkephalin receptors are allosterically coupled.