Characteristics of non-opioid beta-endorphin receptor

Tritium-labeled selective agonist of non-opioid beta-endorphin receptor, the decapeptide immunorphine ([3H]SLTCLVKGFY) with specific activity of 24 Ci/mmol has been prepared. By its use, non-opioid beta-endorphin receptors were revealed and characterized on mouse peritoneal macrophages and rat myocardium, spleen, adrenal, and brain membranes. The non-opioid beta-endorphin receptor of macrophages has in addition to immunorphine (Kd of the [3H]immunorphine-receptor complex was 2.4 +/- 0.1 nM) and beta-endorphin (Ki of the [3H]immunorphine specific binding was 2.9 +/- 0.2 nM) a high affinity for Fc-fragment of human IgG1, pentarphine (VKGFY), cyclopentarphine [cyclo(VKGFY)], and [Pro3]pentarphine (VKPFY) (Ki values were 0.0060 +/- 0.0004, 2.7 +/- 0.2, 2.6 +/- 0.2, and 2.8 +/- 0.2 nM, respectively) and is insensitive to naloxone and [Met5]enkephalin (Ki > 100 microM). Treatment of macrophages with trypsin resulted in the loss of their ability for the specific binding of [3H]immunorphine. Values of the specific binding of 8.4 nM [3H]immunorphine to rat adrenal, spleen, myocardium, and brain membranes were determined to be 1146.0 +/- 44.7, 698.6 +/- 28.1, 279.1 +/- 15.4, and 172.2 +/- 1.8 fmol/mg protein, respectively. Unlabeled beta-endorphin, pentarphine, [Pro3]pentarphine, cyclopentarphine, cyclodipentarphine [cyclo(VKGFYVKGFY)], and Fc-fragment of IgG1 inhibited the binding of [3H]immunorphine to membranes from these organs. No specific binding of [3H]immunorphine to rat liver, lung, kidney, and intestine membranes was found.