Distinct molecular forms of opiate binding in the frog brain.
In frog brain membranes, equilibrium saturation binding of the opiate agonist: 3H-etorphine and of the opiate antagonist: 3H-diprenorphine is biphasic. In the presence of sodium ions (120 mM), "kinetic conversions" (unchanged Bmax) are observed: high affinity binding of the 3H-agonist is decreased while high affinity binding of the antagonist is increased. Frog brain membranes were labelled either with 3H-etorphine or with 3H-diprenorphine and solubilized with digitonin. The soluble extracts were centrifuged in sucrose gradients: two distinct components were labelled which sedimented respectively faster (approximately 12 S) and slower (approximately 10 S) than did catalase, used as marker. Pre-incubation of membrane and of 3H-ligand in the presence of 120 mM NaCl resulted in 1) considerably reduced recovery of the 12 S component in labelled form and 2) substantially enhanced labelling of the 10 S component with the 3H-antagonist. Gpp(NH)p (guanyl-5'-yl imidodiphosphate) exerted similar effects as did sodium ions. Taken together, these data suggest that the two components in question represent physically distinct agonist and antagonist forms of frog brain opiate receptors.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004072:Digitonin; D004174:Diprenorphine / Q000378:metabolism*; D005048:Etorphine / Q000378:metabolism*; D009019:Morphinans / Q000378:metabolism*; D011898:Ranidae; D011957:Receptors, Opioid / Q000378:metabolism*; D012995:Solubility
D009019:Morphinans; D011957:Receptors, Opioid; D004174:Diprenorphine; D005048:Etorphine; D004072:Digitonin