Characterization, solubilization and purification of an opioid receptor from the brain of the frog Rana ridibunda.

The brain of the frog R. ridibunda contains a major opioid binding site which in vitro pharmacological profile is different from those of mammalian mu, delta- and kappa-opioid sites. In digitonin extracts, this major opioid site exists as two molecular forms -10S and 12S- which are clearly resolved by sedimentation in sucrose gradients and which are thought to represent the opioid receptor alone (10S) or associated (12S) with a guanine nucleotide regulatory protein. Purification of the digitonin extracts by affinity chromatography on immobilized dynorphin, results in a single major protein component of apparent Mr approximately 64,000.